Hydrogen

Formula: H₂
Molecular weight: 2.01588
IUPAC Standard InChI:
InChI=1S/H2/h1H

Download the identifier in a file.
IUPAC Standard InChIKey: UFHFLCQGNIYNRP-UHFFFAOYSA-N
CAS Registry Number: 1333-74-0
Chemical structure:
This structure is also available as a 2d Mol file or as a computed 3d SD file
The 3d structure may be viewed using Java or Javascript.
Isotopologues:
Other names: Dihydrogen; o-Hydrogen; p-Hydrogen; Molecular hydrogen; H2; UN 1049; UN 1966
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Information on this page:
Other data available:
- Reaction thermochemistry data: reactions 51 to 100, reactions 101 to 150, reactions 151 to 200, reactions 201 to 250, reactions 251 to 300, reactions 301 to 350, reactions 351 to 400, reactions 401 to 450, reactions 451 to 500, reactions 501 to 550, reactions 551 to 600, reactions 601 to 621
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Gas phase thermochemistry data

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Quantity	Value	Units	Method	Reference	Comment
S°_{gas,1 bar}	31.2333 ± 0.0007	cal/mol*K	Review	Cox, Wagman, et al., 1984	CODATA Review value
S°_{gas,1 bar}	31.233	cal/mol*K	Review	Chase, 1998	Data last reviewed in March, 1977

Gas Phase Heat Capacity (Shomate Equation)

C_p° = A + B*t + C*t² + D*t³ + E/t²
H° − H°_298.15= A*t + B*t²/2 + C*t³/3 + D*t⁴/4 − E/t + F − H
S° = A*ln(t) + B*t + C*t²/2 + D*t³/3 − E/(2*t²) + G
C_p = heat capacity (cal/mol*K)
H° = standard enthalpy (kcal/mol)
S° = standard entropy (cal/mol*K)
t = temperature (K) / 1000.

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View table.

Temperature (K)	298. - 1000.	1000. - 2500.	2500. - 6000.
A	7.903006	4.436683	10.376090
B	-2.715922	2.929578	-1.026071
C	2.732508	-0.683505	0.304117
D	-0.662733	0.064110	-0.023154
E	-0.037896	0.472751	-4.907711
F	-2.385468	-0.274244	-9.205344
G	41.278196	37.353760	38.738373
H	0.0	0.0	0.0
Reference	Chase, 1998	Chase, 1998	Chase, 1998
Comment	Data last reviewed in March, 1977; New parameter fit October 2001	Data last reviewed in March, 1977; New parameter fit October 2001	Data last reviewed in March, 1977; New parameter fit October 2001

Phase change data

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Data compiled as indicated in comments:
TRC - Thermodynamics Research Center, NIST Boulder Laboratories, Kenneth Kroenlein director

Quantity	Value	Units	Method	Reference	Comment
T_triple	0.	K	N/A	Roder, Childs, et al., 1973	TRC
T_triple	13.95	K	N/A	Clusius and Weigand, 1940	Uncertainty assigned by TRC = 0.06 K; see property X for dP/dT for c-l equil.; TRC
T_triple	13.96	K	N/A	Henning and Otto, 1936	Uncertainty assigned by TRC = 0.05 K; temperature measured with He gas thermometer; TRC
Quantity	Value	Units	Method	Reference	Comment
P_triple	0.	atm	N/A	Roder, Childs, et al., 1973	TRC
P_triple	0.0712	atm	N/A	Henning and Otto, 1936	Uncertainty assigned by TRC = 0.0004 atm; TRC
Quantity	Value	Units	Method	Reference	Comment
T_c	33.18	K	N/A	Onnes, Crommelin, et al., 1917	Uncertainty assigned by TRC = 0.2 K; derived from P-V-T measurements; TRC
Quantity	Value	Units	Method	Reference	Comment
P_c	12.83	atm	N/A	Onnes, Crommelin, et al., 1917	Uncertainty assigned by TRC = 0.0117 atm; derived from vapor pressure extrapolated to Tc; TRC
Quantity	Value	Units	Method	Reference	Comment
_c	15.4	mol/l	N/A	Onnes, Crommelin, et al., 1917	Uncertainty assigned by TRC = 2. mol/l; by extrapolation of rectilinear diameter to Tc; TRC

Antoine Equation Parameters

log₁₀(P) = A − (B / (T + C))
P = vapor pressure (atm)
T = temperature (K)

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Temperature (K)	A	B	C	Reference	Comment
21.01 - 32.27	3.53743	99.395	7.726	van Itterbeek, Verbeke, et al., 1964	Coefficents calculated by NIST from author's data.

In addition to the Thermodynamics Research Center (TRC) data available from this site, much more physical and chemical property data is available from the following TRC products:

Reaction thermochemistry data

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Data compiled as indicated in comments:
MS - José A. Martinho Simões
M - Michael M. Meot-Ner (Mautner) and Sharon G. Lias
ALS - Hussein Y. Afeefy, Joel F. Liebman, and Stephen E. Stein
B - John E. Bartmess

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Reactions 1 to 50

(solution) + Hydrogen (solution) = 2 (solution)

By formula: C₈Co₂O₈ (solution) + H₂ (solution) = 2C₄HCoO₄ (solution)

Quantity	Value	Units	Method	Reference	Comment
_rH°	4.7 ± 0.2	kcal/mol	EqS	Rathke, Klingler, et al., 1992	solvent: Supercritical carbon dioxide; Temperature range: 333-453 K. The results corrected for 1 atm pressure of H2 are 3.99 kcal/mol and -17.6 J/(mol K) Rathke, Klingler, et al., 1992; MS
_rH°	3.1 ± 0.2	kcal/mol	EqS	Bor, 1986	solvent: n-Hexane; Temperature range: ca. 300-420 K; MS
_rH°	6.31	kcal/mol	KinS	Alemdaroglu, Penninger, et al., 1976	solvent: n-Heptane; The reaction enthalpy relies on the experimental values for the forward and reverse activation enthalpies, 72.4 and 11.0 kcal/mol, respectively Alemdaroglu, Penninger, et al., 1976. A rather different value has, however, been reported for the activation enthalpy of the forward reaction, 25.00 kcal/mol Ungváry, 1972; MS
_rH°	6.60	kcal/mol	EqS	Alemdaroglu, Penninger, et al., 1976	solvent: n-Heptane; Temperature range: 353-428 K; MS
_rH°	3.20	kcal/mol	EqS	Ungváry, 1972	solvent: n-Heptane; Temperature range: 307-428 K. The results corrected for 1 atm pressure of H2 are 4.30 kcal/mol and -10.9 J/(mol K) Rathke, Klingler, et al., 1992; MS

H₃⁺ + Hydrogen = (H₃⁺ )

By formula: H₃⁺ + H₂ = (H₃⁺ H₂)

Quantity	Value	Units	Method	Reference	Comment
_rH°	6.9 ± 0.4	kcal/mol	AVG	N/A	Average of 4 out of 11 values; Individual data points
Quantity	Value	Units	Method	Reference	Comment
_rS°	17.4 - 17.4	cal/mol*K	RNG	N/A	Range of 6 values; Individual data points

C₁₁H₂O₁₁Os (solution) + (solution) = Hydrogen (g) + (solution)

By formula: C₁₁H₂O₁₁Os (solution) + CO (solution) = H₂ (g) + C₁₂O₁₂Os₃ (solution)

Quantity	Value	Units	Method	Reference	Comment
_rH°	-9.0 ± 2.3	kcal/mol	ES/KS	Poë, Sampson, et al., 1993	solvent: Decalin; Calculated from equilibrium and kinetic data Poë, Sampson, et al., 1993.; MS
_rH°	-18.5 ± 2.3	kcal/mol	N/A	Poë, Sampson, et al., 1993	solvent: Decalin; Calculated from data for the reactions Os3(CO)10(H)2(solution) + CO(solution) = Os3(CO)11(H)2(solution) (hrxn [kJ/mol]=-39.7±1.3, srxn [J/(mol K)]=-80.3±3.8) and Os3(CO)11(H)2(solution) + CO(solution) = Os3(CO)12(solution) + H2(g) (hrxn [kJ/mol]=-37.7±9.6, srxn [J/(mol K)]=-32.6±27.6) Poë, Sampson, et al., 1993.; MS

+ Hydrogen =

By formula: C₆H₁₀ + H₂ = C₆H₁₂

Quantity	Value	Units	Method	Reference	Comment
_rH°	-28. ± 1.	kcal/mol	AVG	N/A	Average of 8 values; Individual data points

(cr) + Hydrogen (g) = 2C₈H₆CrO₃ (cr)

By formula: C₁₆H₁₀Cr₂O₆ (cr) + H₂ (g) = 2C₈H₆CrO₃ (cr)

Quantity	Value	Units	Method	Reference	Comment
_rH°	-3.32 ± 0.96	kcal/mol	RSC	Landrum and Hoff, 1985	The reaction enthalpy was obtained from the value for the reaction 2Cr(Cp)(CO)3(H)(cr) + 1,3-cy-C6H8(solution) = [Cr(Cp)(CO)3]2(cr) + cy-C6H10(solution), -23.5 ± 0.91 kcal/mol Landrum and Hoff, 1985, together with the calculated enthalpy for 1,3-cy-C6H8(l) + H2(g) = cy-C6H10(l), -112.2±1.3 Pedley, 1994. It was assumed that 1,3-cy-C6H8 and cy-C6H10 have similar solution enthalpies in heptane; MS
_rH°	-3.6 ± 1.0	kcal/mol	DSC	Landrum and Hoff, 1985	The reaction enthalpy was obtained from the value for the reaction 2Cr(Cp)(CO)3(H)(cr) + 1,3-cy-C6H8(solution) = [Cr(Cp)(CO)3]2(cr) + cy-C6H10(solution), -23.5 ± 0.91 kcal/mol Landrum and Hoff, 1985, together with the calculated enthalpy for 1,3-cy-C6H8(l) + H2(g) = cy-C6H10(l), -112.2±1.3 Pedley, 1994. It was assumed that 1,3-cy-C6H8 and cy-C6H10 have similar solution enthalpies in heptane; MS

Hydrogen + =

By formula: H₂ + C₆H₁₂ = C₆H₁₄

Quantity	Value	Units	Method	Reference	Comment
_rH°	-30.0 ± 0.6	kcal/mol	AVG	N/A	Average of 8 values; Individual data points

(H₃⁺ Hydrogen ) + = (H₃⁺ 2)

By formula: (H₃⁺ H₂) + H₂ = (H₃⁺ 2H₂)

Quantity	Value	Units	Method	Reference	Comment
_rH°	3.3 ± 0.2	kcal/mol	PHPMS	Hiraoka, 1987	gas phase; M
_rH°	3.1	kcal/mol	HPMS	Beuhler, Ehrenson, et al., 1983	gas phase; M
_rH°	3.4	kcal/mol	HPMS	Beuhler, Ehrenson, et al., 1983	gas phase; deuterated; M
_rH°	4.1	kcal/mol	PHPMS	Hiraoka and Kebarle, 1975	gas phase; M
_rH°	1.8	kcal/mol	HPMS	Bennett and Field, 1972	gas phase; Entropy change is questionable; M
Quantity	Value	Units	Method	Reference	Comment
_rS°	17.4	cal/mol*K	PHPMS	Hiraoka, 1987	gas phase; M
_rS°	16.9	cal/mol*K	HPMS	Beuhler, Ehrenson, et al., 1983	gas phase; M
_rS°	16.1	cal/mol*K	HPMS	Beuhler, Ehrenson, et al., 1983	gas phase; deuterated; M
_rS°	19.8	cal/mol*K	PHPMS	Hiraoka and Kebarle, 1975	gas phase; M
_rS°	10.8	cal/mol*K	HPMS	Bennett and Field, 1972	gas phase; Entropy change is questionable; M

Hydrogen + =

By formula: H₂ + C₇H₁₄ = C₇H₁₆

Quantity	Value	Units	Method	Reference	Comment
_rH°	-29.8 ± 0.5	kcal/mol	AVG	N/A	Average of 6 values; Individual data points

+ Hydrogen =

By formula: C₈H₁₆ + H₂ = C₈H₁₈

Quantity	Value	Units	Method	Reference	Comment
_rH°	-30. ± 2.	kcal/mol	AVG	N/A	Average of 7 values; Individual data points

+ = Hydrogen

By formula: H^- + H⁺ = H₂

Quantity	Value	Units	Method	Reference	Comment
_rH°	400.40	kcal/mol	N/A	Shiell, Hu, et al., 2000	gas phase; Given: 139714.8±1 cm-1 at 0K, or 399.465±0.003 kcal/mol; B
_rH°	400.40	kcal/mol	N/A	Pratt, McCormack, et al., 1992	gas phase; 399.46±0.01 kcal/mol at 0K; 0.94 correction, Gurvich, Veyts, et al.; B
_rH°	400.40	kcal/mol	D-EA	Lykke, Murray, et al., 1991	gas phase; Reported: 6082.99±0.15 cm-1, or 0.754195(18) eV; B
Quantity	Value	Units	Method	Reference	Comment
_rG°	394.20 ± 0.10	kcal/mol	H-TS	Shiell, Hu, et al., 2000	gas phase; Given: 139714.8±1 cm-1 at 0K, or 399.465±0.003 kcal/mol; B
_rG°	394.20	kcal/mol	H-TS	Lykke, Murray, et al., 1991	gas phase; Reported: 6082.99±0.15 cm-1, or 0.754195(18) eV; B

Hydrogen + =

By formula: H₂ + C₅H₈ = C₅H₁₀

Quantity	Value	Units	Method	Reference	Comment
_rH°	-26.94 ± 0.13	kcal/mol	Chyd	Allinger, Dodziuk, et al., 1982	liquid phase; solvent: Hexane; ALS
_rH°	-26.8 ± 0.2	kcal/mol	Chyd	Roth and Lennartz, 1980	liquid phase; solvent: Cyclohexane; ALS
_rH°	-26.04 ± 0.44	kcal/mol	Chyd	Turner, Jarrett, et al., 1973	liquid phase; solvent: Acetic acid; ALS
_rH°	-26.2 ± 0.2	kcal/mol	Chyd	Rogers and McLafferty, 1971	liquid phase; solvent: Hydrocarbon; ALS
_rH°	-26.67 ± 0.06	kcal/mol	Chyd	Dolliver, Gresham, et al., 1937	gas phase; Reanalyzed by Cox and Pilcher, 1970, Original value = -26.92 ± 0.06 kcal/mol; At 355 °K; ALS

Hydrogen + =

By formula: H₂ + C₈H₁₄ = C₈H₁₆

Quantity	Value	Units	Method	Reference	Comment
_rH°	-24.3	kcal/mol	Chyd	Doering, Roth, et al., 1989	liquid phase; ALS
_rH°	-24.5 ± 0.2	kcal/mol	Chyd	Roth and Lennartz, 1980	liquid phase; solvent: Cyclohexane; ALS
_rH°	-23.04 ± 0.17	kcal/mol	Chyd	Rogers, Von Voithenberg, et al., 1978	liquid phase; solvent: Hexane; ALS
_rH°	-23.0 ± 0.1	kcal/mol	Chyd	Turner and Meador, 1957	liquid phase; solvent: Acetic acid; ALS
_rH°	-23.28 ± 0.15	kcal/mol	Chyd	Conn, Kistiakowsky, et al., 1939	gas phase; Reanalyzed by Cox and Pilcher, 1970, Original value = -23.53 ± 0.04 kcal/mol; At 355 K; ALS

0.5C₃₆H₈₄Cl₂P₄Rh₂ (solution) + Hydrogen (g) = C₁₈H₄₄ClP₂Rh (solution)

By formula: 0.5C₃₆H₈₄Cl₂P₄Rh₂ (solution) + H₂ (g) = C₁₈H₄₄ClP₂Rh (solution)

Quantity	Value	Units	Method	Reference	Comment
_rH°	-23.6 ± 0.65	kcal/mol	RSC	Wang, Rosini, et al., 1995	solvent: Benzene; The reaction enthalpy was calculated from the enthalpies of the reactions Rh[P(i-Pr)3]2(Cl)(H)2(solution) + t-BuNC(solution) = Rh[P(i-Pr)3]2(Cl)(CN-t-Bu)(solution) + H2(g), -9.89 ± 0.41 kcal/mol, and 0.5{Rh[P(i-Pr)3]2(Cl)}2(solution) + t-BuNC(solution) = Rh[P(i-Pr)3]2(Cl)(CN-t-Bu)(solution), -33.51 ± 0.50 kcal/mol Wang, Rosini, et al., 1995. The enthalpy of solution of {Rh[P(i-Pr)3]2(Cl)}2(cr) was measured as 4.80 ± 0.31 kcal/mol Wang, Rosini, et al., 1995.; MS

Hydrogen + =

By formula: H₂ + C₆H₁₀ = C₆H₁₂

Quantity	Value	Units	Method	Reference	Comment
_rH°	-24.09 ± 0.15	kcal/mol	Chyd	Rogers, Crooks, et al., 1987	liquid phase; ALS
_rH°	-24.22 ± 0.12	kcal/mol	Chyd	Allinger, Dodziuk, et al., 1982	liquid phase; solvent: Hexane; ALS
_rH°	-23.01 ± 0.04	kcal/mol	Chyd	Turner and Garner, 1958	liquid phase; solvent: Acetic acid; ALS
_rH°	-23.01 ± 0.04	kcal/mol	Chyd	Turner and Garner, 1957	liquid phase; solvent: Acetic acid; ALS
_rH°	-23.01 ± 0.04	kcal/mol	Chyd	Turner and Garner, 1957, 2	liquid phase; solvent: Acetic acid; ALS

2 Hydrogen + =

By formula: 2H₂ + C₆H₁₀ = C₆H₁₄

Quantity	Value	Units	Method	Reference	Comment
_rH°	-60.3 ± 0.4	kcal/mol	Chyd	Fang and Rogers, 1992	liquid phase; solvent: Cyclohexane; ALS
_rH°	-60.69 ± 0.65	kcal/mol	Chyd	Molnar, Rachford, et al., 1984	liquid phase; solvent: Dioxane; ALS
_rH°	-60.17 ± 0.37	kcal/mol	Chyd	Turner, Mallon, et al., 1973	liquid phase; solvent: Glacial acetic acid; ALS
_rH°	-60.03 ± 0.10	kcal/mol	Chyd	Kistiakowsky, Ruhoff, et al., 1936	gas phase; Reanalyzed by Cox and Pilcher, 1970, Original value = -60.53 ± 0.15 kcal/mol; At 355 °K; ALS

Hydrogen + =

By formula: H₂ + C₇H₁₂ = C₇H₁₄

Quantity	Value	Units	Method	Reference	Comment
_rH°	-24.36 ± 0.15	kcal/mol	Chyd	Allinger, Dodziuk, et al., 1982	liquid phase; solvent: Hexane; ALS
_rH°	-23.5 ± 0.2	kcal/mol	Chyd	Rogers and McLafferty, 1971	liquid phase; solvent: Hydrocarbon; ALS
_rH°	-23.56 ± 0.11	kcal/mol	Chyd	Turner and Garner, 1958	liquid phase; solvent: Acetic acid; ALS
_rH°	-23.56 ± 0.11	kcal/mol	Chyd	Turner and Garner, 1957	liquid phase; solvent: Acetic acid; ALS

Hydrogen + =

By formula: H₂ + C₇H₁₂ = C₇H₁₄

Quantity	Value	Units	Method	Reference	Comment
_rH°	-25.6 ± 0.1	kcal/mol	Chyd	Allinger, Dodziuk, et al., 1982	liquid phase; solvent: Hexane; ALS
_rH°	-24.2 ± 0.2	kcal/mol	Chyd	Rogers and McLafferty, 1971	liquid phase; solvent: Hydrocarbon; ALS
_rH°	-24.88 ± 0.12	kcal/mol	Chyd	Turner and Garner, 1958	liquid phase; solvent: Acetic acid; ALS
_rH°	-24.88 ± 0.12	kcal/mol	Chyd	Turner and Garner, 1957	liquid phase; solvent: Acetic acid; ALS

Hydrogen + =

By formula: H₂ + C₆H₁₀ = C₆H₁₂

Quantity	Value	Units	Method	Reference	Comment
_rH°	-27.70 ± 0.23	kcal/mol	Chyd	Allinger, Dodziuk, et al., 1982	liquid phase; solvent: Hexane; ALS
_rH°	-26.88 ± 0.02	kcal/mol	Chyd	Turner and Garner, 1958	liquid phase; solvent: Acetic acid; ALS
_rH°	-26.85 ± 0.05	kcal/mol	Chyd	Turner and Garner, 1957	liquid phase; solvent: Acetic acid; ALS
_rH°	-26.82 ± 0.08	kcal/mol	Chyd	Turner and Garner, 1957, 2	liquid phase; solvent: Acetic acid; ALS

C₃H₇⁺ + Hydrogen = (C₃H₇⁺ )

By formula: C₃H₇⁺ + H₂ = (C₃H₇⁺ H₂)

Quantity	Value	Units	Method	Reference	Comment
_rH°	2.5	kcal/mol	PHPMS	Hiraoka and Kebarle, 1976	gas phase; Entropy change calculated or estimated, DG<, «DELTA»_rH<; M
Quantity	Value	Units	Method	Reference	Comment
_rS°	20.	cal/mol*K	N/A	Hiraoka and Kebarle, 1976	gas phase; Entropy change calculated or estimated, DG<, «DELTA»_rH<; M

Free energy of reaction

_rG° (kcal/mol)	T (K)	Method	Reference	Comment
0.9	170.	PHPMS	Hiraoka and Kebarle, 1976	gas phase; Entropy change calculated or estimated, DG<, «DELTA»_rH<; M

+ Hydrogen = ( )

By formula: Co⁺ + H₂ = (Co⁺ H₂)

Quantity	Value	Units	Method	Reference	Comment
_rH°	20. ± 1.	kcal/mol	SIDT	Kemper, Bushnell, et al., 1993	gas phase; «DELTA»_rH(O K)=18.2 kcal/mol, «DELTA»_rS(300 K)=20.6 cal/mol*K; M
Quantity	Value	Units	Method	Reference	Comment
_rS°	22.0	cal/mol*K	SIDT	Kemper, Bushnell, et al., 1993	gas phase; «DELTA»_rH(O K)=18.2 kcal/mol, «DELTA»_rS(300 K)=20.6 cal/mol*K; M

Enthalpy of reaction

_rH° (kcal/mol)	T (K)	Method	Reference	Comment
17.5 (+2.3,-0.)		CID	Haynes and Armentrout, 1996	gas phase; guided ion beam CID; M

+ Hydrogen =

By formula: C₅H₁₀ + H₂ = C₅H₁₂

Quantity	Value	Units	Method	Reference	Comment
_rH°	-30.27 ± 0.58	kcal/mol	Chyd	Molnar, Rachford, et al., 1984	liquid phase; solvent: Dioxane; ALS
_rH°	-29.87 ± 0.42	kcal/mol	Chyd	Molnar, Rachford, et al., 1984	liquid phase; solvent: Hexane; ALS
_rH°	-29.30 ± 0.57	kcal/mol	Chyd	Rogers and Skanupong, 1974	liquid phase; solvent: Hexane; ALS
_rH°	-28.5 ± 0.3	kcal/mol	Chyd	Rogers and McLafferty, 1971	liquid phase; solvent: Hydrocarbon; ALS

+ Hydrogen =

By formula: C₇H₁₂ + H₂ = C₇H₁₄

Quantity	Value	Units	Method	Reference	Comment
_rH°	-28.56 ± 0.16	kcal/mol	Chyd	Rogers, Crooks, et al., 1987	liquid phase; ALS
_rH°	-27.75 ± 0.13	kcal/mol	Chyd	Turner and Garner, 1958	liquid phase; solvent: Acetic acid; ALS
_rH°	-27.75 ± 0.13	kcal/mol	Eqk	Turner and Garner, 1957	liquid phase; solvent: Acetic acid; ALS
_rH°	-28.70 ± 0.07	kcal/mol	Chyd	Turner and Garner, 1957, 2	liquid phase; solvent: Acetic acid; ALS

Hydrogen + =

By formula: H₂ + C₇H₁₂ = C₇H₁₄

Quantity	Value	Units	Method	Reference	Comment
_rH°	-26.4 ± 0.1	kcal/mol	Chyd	Roth and Lennartz, 1980	liquid phase; solvent: Cyclohexane; ALS
_rH°	-25.85 ± 0.09	kcal/mol	Chyd	Turner, Meador, et al., 1957	liquid phase; solvent: Acetic acid; ALS
_rH°	-26.02 ± 0.15	kcal/mol	Chyd	Conn, Kistiakowsky, et al., 1939	gas phase; Reanalyzed by Cox and Pilcher, 1970, Original value = -26.52 ± 0.02 kcal/mol; At 355 K; ALS

3 Hydrogen + =

By formula: 3H₂ + C₇H₈ = C₇H₁₄

Quantity	Value	Units	Method	Reference	Comment
_rH°	-72.8 ± 0.1	kcal/mol	Chyd	Roth, Klaerner, et al., 1983	liquid phase; solvent: Isooctane; ALS
_rH°	-70.49 ± 0.39	kcal/mol	Chyd	Turner, Meador, et al., 1957	liquid phase; solvent: Acetic acid; ALS
_rH°	-72.11 ± 0.30	kcal/mol	Chyd	Conn, Kistiakowsky, et al., 1939	gas phase; Reanalyzed by Cox and Pilcher, 1970, Original value = -72.85 ± 0.01 kcal/mol; at 355 K; ALS

2 Hydrogen + =

By formula: 2H₂ + C₆H₁₀ = C₆H₁₄

Quantity	Value	Units	Method	Reference	Comment
_rH°	-55.31 ± 0.72	kcal/mol	Chyd	Molnar, Rachford, et al., 1984	liquid phase; solvent: Dioxane; ALS
_rH°	-54.26 ± 0.67	kcal/mol	Chyd	Molnar, Rachford, et al., 1984	liquid phase; solvent: Hexane; ALS
_rH°	-53.39 ± 0.15	kcal/mol	Chyd	Dolliver, Gresham, et al., 1937	gas phase; Reanalyzed by Cox and Pilcher, 1970, Original value = -53.87 ± 0.15 kcal/mol; At 355 °K; ALS

+ 3 Hydrogen =

By formula: C₅H₅N + 3H₂ = C₅H₁₁N

Quantity	Value	Units	Method	Reference	Comment
_rH°	-46.31 ± 0.18	kcal/mol	Eqk	Hales and Herington, 1957	gas phase; Reanalyzed by Cox and Pilcher, 1970, Original value = -48.32 ± 0.18 kcal/mol; At 400-550 K; ALS
_rH°	-46.12 ± 0.50	kcal/mol	Eqk	Burrows and King, 1935	liquid phase; Reanalyzed by Cox and Pilcher, 1970, Original value = -45.00 kcal/mol; At 423-443 K; ALS

+ Hydrogen =

By formula: C₈H₁₆ + H₂ = C₈H₁₈

Quantity	Value	Units	Method	Reference	Comment
_rH°	-25.5	kcal/mol	Chyd	Turner, Nettleton, et al., 1958	liquid phase; solvent: Acetic acid; ALS
_rH°	-26.99 ± 0.06	kcal/mol	Chyd	Dolliver, Gresham, et al., 1937	gas phase; Reanalyzed by Cox and Pilcher, 1970, Original value = -27.24 ± 0.06 kcal/mol; At 355 °K; ALS
_rH°	-28.58 ± 0.80	kcal/mol	Chyd	Crawford and Parks, 1936	liquid phase; ALS

+ Hydrogen =

By formula: C₃H₆ + H₂ = C₃H₈

Quantity	Value	Units	Method	Reference	Comment
_rH°	-29.5 ± 1.2	kcal/mol	Chyd	Kistiakowsky and Nickle, 1951	gas phase; Reanalyzed by Cox and Pilcher, 1970, Original value = -29.85 ± 0.50 kcal/mol; ALS
_rH°	-29.87 ± 0.10	kcal/mol	Chyd	Kistiakowsky, Ruhoff, et al., 1935	gas phase; Reanalyzed by Cox and Pilcher, 1970, Original value = -30.115 ± 0.013 kcal/mol; At 355 °K; ALS

( ) + Hydrogen = ( )

By formula: (Co⁺ CH₄) + H₂ = (Co⁺ H₂ CH₄)

Quantity	Value	Units	Method	Reference	Comment
_rS°	22.9	cal/mol*K	SIDT	Kemper, Bushnell, et al., 1993, 2	gas phase; switching reaction(Co+).2H2, «DELTA»_rS(440 K); Kemper, Bushnell, et al., 1993; M

Enthalpy of reaction

_rH° (kcal/mol)	T (K)	Method	Reference	Comment
17.4 (+0.8,-0.)		SIDT	Kemper, Bushnell, et al., 1993, 2	gas phase; switching reaction(Co+).2H2, «DELTA»_rS(440 K); Kemper, Bushnell, et al., 1993; M

Hydrogen + =

By formula: H₂ + C₃H₆O = C₃H₈O

Quantity	Value	Units	Method	Reference	Comment
_rH°	-16.43 ± 0.10	kcal/mol	Cm	Wiberg, Crocker, et al., 1991	liquid phase; ALS
_rH°	-13.20	kcal/mol	Eqk	Buckley and Herington, 1965	gas phase; ALS
_rH°	-13.24 ± 0.10	kcal/mol	Chyd	Dolliver, Gresham, et al., 1938	gas phase; Reanalyzed by Cox and Pilcher, 1970, Original value = -13.4 ± 0.1 kcal/mol; At 355 °K; ALS

( Hydrogen ) + = ( )

By formula: (Co⁺ H₂) + CH₄ = (Co⁺ CH₄ H₂)

Quantity	Value	Units	Method	Reference	Comment
_rS°	21.8	cal/mol*K	SIDT	Kemper, Bushnell, et al., 1993, 2	gas phase; switching reaction(Co+)2H2, «DELTA»_rS(440 K); Kemper, Bushnell, et al., 1993; M

Enthalpy of reaction

_rH° (kcal/mol)	T (K)	Method	Reference	Comment
22.6 (+1.2,-0.)		SIDT	Kemper, Bushnell, et al., 1993, 2	gas phase; switching reaction(Co+)2H2, «DELTA»_rS(440 K); Kemper, Bushnell, et al., 1993; M

+ Hydrogen =

By formula: C₈H₁₄ + H₂ = C₈H₁₆

Quantity	Value	Units	Method	Reference	Comment
_rH°	-26.2 ± 0.3	kcal/mol	Chyd	Rogers and McLafferty, 1971	liquid phase; solvent: Hydrocarbon; ALS
_rH°	-26.32 ± 0.04	kcal/mol	Chyd	Turner and Garner, 1958	liquid phase; solvent: Acetic acid; ALS
_rH°	-26.32 ± 0.04	kcal/mol	Chyd	Turner and Garner, 1957	liquid phase; solvent: Acetic acid; ALS

Hydrogen + =

By formula: H₂ + C₈H₁₄ = C₈H₁₆

Quantity	Value	Units	Method	Reference	Comment
_rH°	-34.5 ± 0.1	kcal/mol	Chyd	Roth, Adamczak, et al., 1991	liquid phase; see Doering, Roth, et al., 1989; ALS
_rH°	-34.41 ± 0.43	kcal/mol	Chyd	Rogers, Von Voithenberg, et al., 1978	liquid phase; solvent: Hexane; ALS
_rH°	-32.24 ± 0.21	kcal/mol	Chyd	Turner and Meador, 1957	liquid phase; solvent: Acetic acid; ALS

( Hydrogen ) + = ( 2)

By formula: (Co⁺ H₂) + H₂ = (Co⁺ 2H₂)

Quantity	Value	Units	Method	Reference	Comment
_rH°	18.0 ± 0.6	kcal/mol	SIDT	Kemper, Bushnell, et al., 1993	gas phase; «DELTA»_rH(0 K)=17.0 kcal/mol, «DELTA»_rS(300 K)=24.5 cal/mol*K; M
Quantity	Value	Units	Method	Reference	Comment
_rS°	24.5	cal/mol*K	SIDT	Kemper, Bushnell, et al., 1993	gas phase; «DELTA»_rH(0 K)=17.0 kcal/mol, «DELTA»_rS(300 K)=24.5 cal/mol*K; M

( 2 Hydrogen ) + = ( 3)

By formula: (Co⁺ 2H₂) + H₂ = (Co⁺ 3H₂)

Quantity	Value	Units	Method	Reference	Comment
_rH°	10.6 ± 0.4	kcal/mol	SIDT	Kemper, Bushnell, et al., 1993	gas phase; «DELTA»_rH(0 K)=9.6 kcal/mol, «DELTA»_rS(300 K)=20.5 cal/mol*K; M
Quantity	Value	Units	Method	Reference	Comment
_rS°	20.5	cal/mol*K	SIDT	Kemper, Bushnell, et al., 1993	gas phase; «DELTA»_rH(0 K)=9.6 kcal/mol, «DELTA»_rS(300 K)=20.5 cal/mol*K; M

( 3 Hydrogen ) + = ( 4)

By formula: (Co⁺ 3H₂) + H₂ = (Co⁺ 4H₂)

Quantity	Value	Units	Method	Reference	Comment
_rH°	10.4 ± 0.6	kcal/mol	SIDT	Kemper, Bushnell, et al., 1993	gas phase; «DELTA»_rH(0 K)=9.6 kcal/mol, «DELTA»_rS(300 K)=25.2 cal/mol*K; M
Quantity	Value	Units	Method	Reference	Comment
_rS°	24.2	cal/mol*K	SIDT	Kemper, Bushnell, et al., 1993	gas phase; «DELTA»_rH(0 K)=9.6 kcal/mol, «DELTA»_rS(300 K)=25.2 cal/mol*K; M

( 4 Hydrogen ) + = ( 5)

By formula: (Co⁺ 4H₂) + H₂ = (Co⁺ 5H₂)

Quantity	Value	Units	Method	Reference	Comment
_rH°	5.2 ± 0.6	kcal/mol	SIDT	Kemper, Bushnell, et al., 1993	gas phase; «DELTA»_rH(0 K)=4.3 kcal/mol, «DELTA»_rS(300 K)=21.9 cal/mol*K; M
Quantity	Value	Units	Method	Reference	Comment
_rS°	22.5	cal/mol*K	SIDT	Kemper, Bushnell, et al., 1993	gas phase; «DELTA»_rH(0 K)=4.3 kcal/mol, «DELTA»_rS(300 K)=21.9 cal/mol*K; M

( 5 Hydrogen ) + = ( 6)

By formula: (Co⁺ 5H₂) + H₂ = (Co⁺ 6H₂)

Quantity	Value	Units	Method	Reference	Comment
_rH°	4.7 ± 0.6	kcal/mol	SIDT	Kemper, Bushnell, et al., 1993	gas phase; «DELTA»_rH(0 K)=4.0 kcal/mol, «DELTA»_rS(300 K)=23.8 cal/mol*K; M
Quantity	Value	Units	Method	Reference	Comment
_rS°	23.7	cal/mol*K	SIDT	Kemper, Bushnell, et al., 1993	gas phase; «DELTA»_rH(0 K)=4.0 kcal/mol, «DELTA»_rS(300 K)=23.8 cal/mol*K; M

( 6 Hydrogen ) + = ( 7)

By formula: (Co⁺ 6H₂) + H₂ = (Co⁺ 7H₂)

Quantity	Value	Units	Method	Reference	Comment
_rH°	1.5 ± 0.7	kcal/mol	SIDT	Kemper, Bushnell, et al., 1993	gas phase; «DELTA»_rH(0 K)=0.8 kcal/mol; «DELTA»_rS(300 K)=18.0 cal/mol*K; M
Quantity	Value	Units	Method	Reference	Comment
_rS°	18.0	cal/mol*K	SIDT	Kemper, Bushnell, et al., 1993	gas phase; «DELTA»_rH(0 K)=0.8 kcal/mol; «DELTA»_rS(300 K)=18.0 cal/mol*K; M

(H₃⁺ 3 Hydrogen ) + = (H₃⁺ 4)

By formula: (H₃⁺ 3H₂) + H₂ = (H₃⁺ 4H₂)

Quantity	Value	Units	Method	Reference	Comment
_rH°	1.7 ± 0.1	kcal/mol	PHPMS	Hiraoka, 1987	gas phase; M
_rH°	2.4	kcal/mol	PHPMS	Hiraoka and Kebarle, 1975	gas phase; M
Quantity	Value	Units	Method	Reference	Comment
_rS°	17.9	cal/mol*K	PHPMS	Hiraoka, 1987	gas phase; M
_rS°	19.3	cal/mol*K	PHPMS	Hiraoka and Kebarle, 1975	gas phase; M

(H₃⁺ 2 Hydrogen ) + = (H₃⁺ 3)

By formula: (H₃⁺ 2H₂) + H₂ = (H₃⁺ 3H₂)

Quantity	Value	Units	Method	Reference	Comment
_rH°	3.2 ± 0.1	kcal/mol	PHPMS	Hiraoka, 1987	gas phase; M
_rH°	3.8	kcal/mol	PHPMS	Hiraoka and Kebarle, 1975	gas phase; M
Quantity	Value	Units	Method	Reference	Comment
_rS°	18.5	cal/mol*K	PHPMS	Hiraoka, 1987	gas phase; M
_rS°	20.2	cal/mol*K	PHPMS	Hiraoka and Kebarle, 1975	gas phase; M

Hydrogen + =

By formula: H₂ + C₈H₁₆ = C₈H₁₈

Quantity	Value	Units	Method	Reference	Comment
_rH°	-28.25 ± 0.1	kcal/mol	Chyd	Rogers, Dejroongruang, et al., 1992	liquid phase; solvent: Cyclohexane; ALS
_rH°	-28.62 ± 0.52	kcal/mol	Chyd	Rogers and Siddiqui, 1975	liquid phase; solvent: n-Hexane; ALS
_rH°	-27.39 ± 0.14	kcal/mol	Chyd	Turner, Jarrett, et al., 1973	liquid phase; solvent: Acetic acid; ALS

2 Hydrogen + =

By formula: 2H₂ + C₈H₁₄ = C₈H₁₈

Quantity	Value	Units	Method	Reference	Comment
_rH°	-64.22 ± 0.26	kcal/mol	Chyd	Rogers, Dagdagan, et al., 1979	liquid phase; solvent: Hexane; ALS
_rH°	-62.80 ± 0.16	kcal/mol	Chyd	Turner, Jarrett, et al., 1973	liquid phase; solvent: Acetic acid; ALS
_rH°	-62.8	kcal/mol	Chyd	Sicher, Svoboda, et al., 1966	liquid phase; solvent: Acetic acid; ALS

Hydrogen + =

By formula: H₂ + C₈H₁₄O = C₈H₁₆O

Quantity	Value	Units	Method	Reference	Comment
_rH°	-13.32	kcal/mol	Chyd	Wiberg, Crocker, et al., 1991	liquid phase; ALS
_rH°	-12.70	kcal/mol	Chyd	Wiberg, Crocker, et al., 1991	solid phase; ALS
_rH°	-9.31	kcal/mol	Chyd	Wiberg, Crocker, et al., 1991	gas phase; ALS
_rH°	-12.70 ± 0.14	kcal/mol	Cm	Wiberg, Crocker, et al., 1991	solid phase; ALS

Hydrogen + =

By formula: H₂ + C₇H₁₂ = C₇H₁₄

Quantity	Value	Units	Method	Reference	Comment
_rH°	-26.63 ± 0.088	kcal/mol	Chyd	Rogers, Crooks, et al., 1987	liquid phase; ALS
_rH°	-25.41 ± 0.11	kcal/mol	Chyd	Turner and Garner, 1958	liquid phase; solvent: Acetic acid; ALS
_rH°	-25.41 ± 0.11	kcal/mol	Chyd	Turner and Garner, 1957	liquid phase; solvent: Acetic acid; ALS

2 Hydrogen + =

By formula: 2H₂ + C₇H₁₀ = C₇H₁₄

Quantity	Value	Units	Method	Reference	Comment
_rH°	-49.92 ± 0.08	kcal/mol	Chyd	Turner, Mallon, et al., 1973	liquid phase; solvent: Glacial acetic acid; ALS
_rH°	-50.77 ± 0.15	kcal/mol	Chyd	Conn, Kistiakowsky, et al., 1939	gas phase; Reanalyzed by Cox and Pilcher, 1970, Original value = -51.26 ± 0.05 kcal/mol; At 355 K; ALS

Hydrogen + =

By formula: H₂ + C₇H₁₀ = C₇H₁₂

Quantity	Value	Units	Method	Reference	Comment
_rH°	-32.8 ± 0.1	kcal/mol	Chyd	Doering, Roth, et al., 1988	gas phase; ALS
_rH°	-33.82 ± 0.28	kcal/mol	Chyd	Rogers, Choi, et al., 1980	liquid phase; solvent: Hexane; Author was aware that data differs from previously reported values; ALS
_rH°	-33.13 ± 0.21	kcal/mol	Chyd	Turner, Meador, et al., 1957	liquid phase; solvent: Acetic acid; ALS

+ Hydrogen =

By formula: C₃H₆O + H₂ = C₃H₈O

Quantity	Value	Units	Method	Reference	Comment
_rH°	-20.14 ± 0.09	kcal/mol	Cm	Wiberg, Crocker, et al., 1991	liquid phase; solvent: Triglyme; Heat of hydrogenation; ALS
_rH°	-16.62 ± 0.18	kcal/mol	Eqk	Connett, 1972	gas phase; At 473-524 K; ALS
_rH°	-15.72 ± 0.16	kcal/mol	Chyd	Buckley and Cox, 1967	gas phase; ALS

2 Hydrogen + =

By formula: 2H₂ + C₆H₈ = C₆H₁₂

Quantity	Value	Units	Method	Reference	Comment
_rH°	-53.64 ± 0.29	kcal/mol	Chyd	Turner, Mallon, et al., 1973	liquid phase; solvent: Glacial acetic acid; ALS
_rH°	-54.88 ± 0.10	kcal/mol	Chyd	Kistiakowsky, Ruhoff, et al., 1936	gas phase; Reanalyzed by Cox and Pilcher, 1970, Original value = -55.4 ± 0.1 kcal/mol; At 355 °K; ALS

(solution) + Hydrogen (solution) = 2 (solution)

By formula: C₁₀Mn₂O₁₀ (solution) + H₂ (solution) = 2C₅HMnO₅ (solution)

Quantity	Value	Units	Method	Reference	Comment
_rH°	8.70 ± 0.31	kcal/mol	EqS	Klingler R.J. and Rathke, 1992	solvent: Supercritical carbon dioxide; Temperature range: 373-463 K; MS

Henry's Law data

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Data compiled by: Rolf Sander

Henry's Law constant (water solution)

k_H(T) = k°_H exp(d(ln(k_H))/d(1/T) ((1/T) - 1/(298.15 K)))
k°_H = Henry's law constant for solubility in water at 298.15 K (mol/kg*bar)
d(ln(k_H))/d(1/T) = Temperature dependence constant (K)

k°_H (mol/kg*bar)	d(ln(k_H))/d(1/T) (K)	Method	Reference	Comment
0.00078	500.	L	N/A
0.00078	640.	Q	N/A	Only the tabulated data between T = 273. K and T = 303. K from missing citation was used to derive k_H and -«DELTA» k_H/R. Above T = 303. K the tabulated data could not be parameterized by equation (reference missing) very well. The partial pressure of water vapor (needed to convert some Henry's law constants) was calculated using the formula given by missing citation. The quantities A and «alpha» from missing citation were assumed to be identical.
0.00078	490.	L	N/A
0.00078		R	N/A

Gas phase ion energetics data

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Data evaluated as indicated in comments:
HL - Edward P. Hunter and Sharon G. Lias
L - Sharon G. Lias

Data compiled as indicated in comments:
B - John E. Bartmess
LL - Sharon G. Lias and Joel F. Liebman
LBLHLM - Sharon G. Lias, John E. Bartmess, Joel F. Liebman, John L. Holmes, Rhoda D. Levin, and W. Gary Mallard
LLK - Sharon G. Lias, Rhoda D. Levin, and Sherif A. Kafafi
RDSH - Henry M. Rosenstock, Keith Draxl, Bruce W. Steiner, and John T. Herron

View reactions leading to H₂⁺ (ion structure unspecified)

Quantity	Value	Units	Method	Reference	Comment
IE (evaluated)	15.42593 ± 0.00005	eV	N/A	N/A	L
Quantity	Value	Units	Method	Reference	Comment
Proton affinity (review)	100.9	kcal/mol	N/A	Hunter and Lias, 1998	HL
Quantity	Value	Units	Method	Reference	Comment
Gas basicity	94.34	kcal/mol	N/A	Hunter and Lias, 1998	HL

Ionization energy determinations

IE (eV)	Method	Reference	Comment
15.425927	EVAL	Shiner, Gilligan, et al., 1993	T = 0K; LL
15.425930	EVAL	Shiner, Gilligan, et al., 1993	T = 0K; LL
15.425932 ± 0.000002	S	McCormack, Gilligan, et al., 1989	T = 0K; LL
15.429558 ± 0.00001	LS	Glab and Hessler, 1987	T = 0K; LBLHLM
15.433174 ± 0.00001	LS	Glab and Hessler, 1987	T = 0K; LBLHLM
15.425942 ± 0.00001	LS	Glab and Hessler, 1987	T = 0K; LBLHLM
15.425932	S	Eyler, Short, et al., 1986	T = 0K; LBLHLM
15.425929	S	Eyler, Short, et al., 1986	T = 0K; LBLHLM
15.425930 ± 0.000027	N/A	Eyler, Short, et al., 1986	LBLHLM
15.5 ± 1.0	S	Farber, Srivastava, et al., 1982	LBLHLM
15.98	PE	Kimura, Katsumata, et al., 1981	LLK
15.43	PE	Bieri, Schmelzer, et al., 1980	LLK
15.42589	EVAL	Huber and Herzberg, 1979	LLK
16. ± 1.	EI	Farber and Srivastava, 1977	LLK
15.4	PI	Rabalais, Debies, et al., 1974	LLK
15.43	PE	Lee and Rabalais, 1974	LLK
15.42589 ± 0.00005	S	Herzberg and Jungen, 1972	LLK
15.4256 ± 0.0001	S	Takezawa, 1970	RDSH
15.38186 ± 0.00031	PE	Asbrink, 1970	RDSH
15.44 ± 0.01	EI	Lossing and Semeluk, 1969	RDSH
15.4256	S	Herzberg, 1969	RDSH
15.431 ± 0.022	TE	Villarejo, 1968	RDSH
15.439 ± 0.015	PE	Collin and Natalis, 1968	RDSH
15.43	CI	Cermak, 1968	RDSH
15.37 ± 0.05	EI	Kerwin, Marmet, et al., 1963	RDSH
15.4269 ± 0.0016	S	Beutler and Junger, 1936	RDSH

Appearance energy determinations

Ion	AE (eV)	Other Products	Method	Reference	Comment
H⁺	18.078 ± 0.003	H	PIPECO	Weitzel, Mahnert, et al., 1994	T = 0K; LL
H⁺	18.0 ± 0.2	H	EI	Crowe and McConkey, 1973	LLK
H⁺	17.28 ± 0.16	H^-	EI	Locht and Momigny, 1971	LLK
H⁺	17.3	H^-	EI	Curran, Laboratories	RDSH

De-protonation reactions

+ = Hydrogen

By formula: H^- + H⁺ = H₂

Quantity	Value	Units	Method	Reference	Comment
_rH°	400.40	kcal/mol	N/A	Shiell, Hu, et al., 2000	gas phase; Given: 139714.8±1 cm-1 at 0K, or 399.465±0.003 kcal/mol; B
_rH°	400.40	kcal/mol	N/A	Pratt, McCormack, et al., 1992	gas phase; 399.46±0.01 kcal/mol at 0K; 0.94 correction, Gurvich, Veyts, et al.; B
_rH°	400.40	kcal/mol	D-EA	Lykke, Murray, et al., 1991	gas phase; Reported: 6082.99±0.15 cm-1, or 0.754195(18) eV; B
Quantity	Value	Units	Method	Reference	Comment
_rG°	394.20 ± 0.10	kcal/mol	H-TS	Shiell, Hu, et al., 2000	gas phase; Given: 139714.8±1 cm-1 at 0K, or 399.465±0.003 kcal/mol; B
_rG°	394.20	kcal/mol	H-TS	Lykke, Murray, et al., 1991	gas phase; Reported: 6082.99±0.15 cm-1, or 0.754195(18) eV; B

Ion clustering data

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Data compiled by: Michael M. Meot-Ner (Mautner) and Sharon G. Lias

Note: Please consider using the reaction search for this species. This page allows searching of all reactions involving this species. Searches may be limited to ion clustering reactions. A general reaction search form is also available.

Clustering reactions

Ar⁺ + Hydrogen = (Ar⁺ )

By formula: Ar⁺ + H₂ = (Ar⁺ H₂)

Quantity	Value	Units	Method	Reference	Comment
_rH°	22.4	kcal/mol	FA	Shul, Passarella, et al., 1987	gas phase; switching reaction(Ar+)Ar, «DELTA»_rH>; Dehmer and Pratt, 1982

+ Hydrogen = ( )

By formula: CHO⁺ + H₂ = (CHO⁺ H₂)

Quantity	Value	Units	Method	Reference	Comment
_rH°	3.9	kcal/mol	PHPMS	Hiraoka and Kebarle, 1975, 2	gas phase
Quantity	Value	Units	Method	Reference	Comment
_rS°	20.5	cal/mol*K	PHPMS	Hiraoka and Kebarle, 1975, 2	gas phase

CH₅⁺ + Hydrogen = (CH₅⁺ )

By formula: CH₅⁺ + H₂ = (CH₅⁺ H₂)

Quantity	Value	Units	Method	Reference	Comment
_rH°	1.88 ± 0.10	kcal/mol	PHPMS	Hiraoka, Kudaka, et al., 1991	gas phase
Quantity	Value	Units	Method	Reference	Comment
_rS°	12.1	cal/mol*K	PHPMS	Hiraoka, Kudaka, et al., 1991	gas phase

(CH₅⁺ Hydrogen ) + = (CH₅⁺ 2)

By formula: (CH₅⁺ H₂) + H₂ = (CH₅⁺ 2H₂)

Quantity	Value	Units	Method	Reference	Comment
_rH°	1.78 ± 0.10	kcal/mol	PHPMS	Hiraoka, Kudaka, et al., 1991	gas phase
Quantity	Value	Units	Method	Reference	Comment
_rS°	16.2	cal/mol*K	PHPMS	Hiraoka, Kudaka, et al., 1991	gas phase

(CH₅⁺ 2 Hydrogen ) + = (CH₅⁺ 3)

By formula: (CH₅⁺ 2H₂) + H₂ = (CH₅⁺ 3H₂)

Quantity	Value	Units	Method	Reference	Comment
_rH°	1.61 ± 0.10	kcal/mol	PHPMS	Hiraoka, Kudaka, et al., 1991	gas phase
Quantity	Value	Units	Method	Reference	Comment
_rS°	22.6	cal/mol*K	PHPMS	Hiraoka, Kudaka, et al., 1991	gas phase

(CH₅⁺ 3 Hydrogen ) + = (CH₅⁺ 4)

By formula: (CH₅⁺ 3H₂) + H₂ = (CH₅⁺ 4H₂)

Quantity	Value	Units	Method	Reference	Comment
_rH°	1.57 ± 0.10	kcal/mol	PHPMS	Hiraoka, Kudaka, et al., 1991	gas phase
Quantity	Value	Units	Method	Reference	Comment
_rS°	25.7	cal/mol*K	PHPMS	Hiraoka, Kudaka, et al., 1991	gas phase

C₃H₇⁺ + Hydrogen = (C₃H₇⁺ )

By formula: C₃H₇⁺ + H₂ = (C₃H₇⁺ H₂)

Quantity	Value	Units	Method	Reference	Comment
_rH°	2.5	kcal/mol	PHPMS	Hiraoka and Kebarle, 1976	gas phase; Entropy change calculated or estimated, DG<, «DELTA»_rH<
Quantity	Value	Units	Method	Reference	Comment
_rS°	20.	cal/mol*K	N/A	Hiraoka and Kebarle, 1976	gas phase; Entropy change calculated or estimated, DG<, «DELTA»_rH<

Free energy of reaction

_rG° (kcal/mol)	T (K)	Method	Reference	Comment
0.9	170.	PHPMS	Hiraoka and Kebarle, 1976	gas phase; Entropy change calculated or estimated, DG<, «DELTA»_rH<

( ) + Hydrogen = ( )

By formula: (Co⁺ CH₄) + H₂ = (Co⁺ H₂ CH₄)

Quantity	Value	Units	Method	Reference	Comment
_rS°	22.9	cal/mol*K	SIDT	Kemper, Bushnell, et al., 1993, 2	gas phase; switching reaction(Co+).2H2, «DELTA»_rS(440 K); Kemper, Bushnell, et al., 1993

Enthalpy of reaction

_rH° (kcal/mol)	T (K)	Method	Reference	Comment
17.4 (+0.8,-0.)		SIDT	Kemper, Bushnell, et al., 1993, 2	gas phase; switching reaction(Co+).2H2, «DELTA»_rS(440 K); Kemper, Bushnell, et al., 1993

( ) + Hydrogen = ( )

By formula: (Co⁺ H₂O) + H₂ = (Co⁺ H₂ H₂O)

Quantity	Value	Units	Method	Reference	Comment
_rS°	24.7	cal/mol*K	SIDT	Kemper, Bushnell, et al., 1993, 2	gas phase; «DELTA»_rS(530 K)

Enthalpy of reaction

_rH° (kcal/mol)	T (K)	Method	Reference	Comment
19.8 (+0.6,-0.)		SIDT	Kemper, Bushnell, et al., 1993, 2	gas phase; «DELTA»_rS(530 K)

+ Hydrogen = ( )

By formula: Co⁺ + H₂ = (Co⁺ H₂)

Quantity	Value	Units	Method	Reference	Comment
_rH°	20. ± 1.	kcal/mol	SIDT	Kemper, Bushnell, et al., 1993	gas phase; «DELTA»_rH(O K)=18.2 kcal/mol, «DELTA»_rS(300 K)=20.6 cal/mol*K
Quantity	Value	Units	Method	Reference	Comment
_rS°	22.0	cal/mol*K	SIDT	Kemper, Bushnell, et al., 1993	gas phase; «DELTA»_rH(O K)=18.2 kcal/mol, «DELTA»_rS(300 K)=20.6 cal/mol*K

Enthalpy of reaction

_rH° (kcal/mol)	T (K)	Method	Reference	Comment
17.5 (+2.3,-0.)		CID	Haynes and Armentrout, 1996	gas phase; guided ion beam CID

( Hydrogen ) + = ( 2)

By formula: (Co⁺ H₂) + H₂ = (Co⁺ 2H₂)

Quantity	Value	Units	Method	Reference	Comment
_rH°	18.0 ± 0.6	kcal/mol	SIDT	Kemper, Bushnell, et al., 1993	gas phase; «DELTA»_rH(0 K)=17.0 kcal/mol, «DELTA»_rS(300 K)=24.5 cal/mol*K
Quantity	Value	Units	Method	Reference	Comment
_rS°	24.5	cal/mol*K	SIDT	Kemper, Bushnell, et al., 1993	gas phase; «DELTA»_rH(0 K)=17.0 kcal/mol, «DELTA»_rS(300 K)=24.5 cal/mol*K

( 2 Hydrogen ) + = ( 3)

By formula: (Co⁺ 2H₂) + H₂ = (Co⁺ 3H₂)

Quantity	Value	Units	Method	Reference	Comment
_rH°	10.6 ± 0.4	kcal/mol	SIDT	Kemper, Bushnell, et al., 1993	gas phase; «DELTA»_rH(0 K)=9.6 kcal/mol, «DELTA»_rS(300 K)=20.5 cal/mol*K
Quantity	Value	Units	Method	Reference	Comment
_rS°	20.5	cal/mol*K	SIDT	Kemper, Bushnell, et al., 1993	gas phase; «DELTA»_rH(0 K)=9.6 kcal/mol, «DELTA»_rS(300 K)=20.5 cal/mol*K

( 3 Hydrogen ) + = ( 4)

By formula: (Co⁺ 3H₂) + H₂ = (Co⁺ 4H₂)

Quantity	Value	Units	Method	Reference	Comment
_rH°	10.4 ± 0.6	kcal/mol	SIDT	Kemper, Bushnell, et al., 1993	gas phase; «DELTA»_rH(0 K)=9.6 kcal/mol, «DELTA»_rS(300 K)=25.2 cal/mol*K
Quantity	Value	Units	Method	Reference	Comment
_rS°	24.2	cal/mol*K	SIDT	Kemper, Bushnell, et al., 1993	gas phase; «DELTA»_rH(0 K)=9.6 kcal/mol, «DELTA»_rS(300 K)=25.2 cal/mol*K

( 4 Hydrogen ) + = ( 5)

By formula: (Co⁺ 4H₂) + H₂ = (Co⁺ 5H₂)

Quantity	Value	Units	Method	Reference	Comment
_rH°	5.2 ± 0.6	kcal/mol	SIDT	Kemper, Bushnell, et al., 1993	gas phase; «DELTA»_rH(0 K)=4.3 kcal/mol, «DELTA»_rS(300 K)=21.9 cal/mol*K
Quantity	Value	Units	Method	Reference	Comment
_rS°	22.5	cal/mol*K	SIDT	Kemper, Bushnell, et al., 1993	gas phase; «DELTA»_rH(0 K)=4.3 kcal/mol, «DELTA»_rS(300 K)=21.9 cal/mol*K

( 5 Hydrogen ) + = ( 6)

By formula: (Co⁺ 5H₂) + H₂ = (Co⁺ 6H₂)

Quantity	Value	Units	Method	Reference	Comment
_rH°	4.7 ± 0.6	kcal/mol	SIDT	Kemper, Bushnell, et al., 1993	gas phase; «DELTA»_rH(0 K)=4.0 kcal/mol, «DELTA»_rS(300 K)=23.8 cal/mol*K
Quantity	Value	Units	Method	Reference	Comment
_rS°	23.7	cal/mol*K	SIDT	Kemper, Bushnell, et al., 1993	gas phase; «DELTA»_rH(0 K)=4.0 kcal/mol, «DELTA»_rS(300 K)=23.8 cal/mol*K

( 6 Hydrogen ) + = ( 7)

By formula: (Co⁺ 6H₂) + H₂ = (Co⁺ 7H₂)

Quantity	Value	Units	Method	Reference	Comment
_rH°	1.5 ± 0.7	kcal/mol	SIDT	Kemper, Bushnell, et al., 1993	gas phase; «DELTA»_rH(0 K)=0.8 kcal/mol; «DELTA»_rS(300 K)=18.0 cal/mol*K
Quantity	Value	Units	Method	Reference	Comment
_rS°	18.0	cal/mol*K	SIDT	Kemper, Bushnell, et al., 1993	gas phase; «DELTA»_rH(0 K)=0.8 kcal/mol; «DELTA»_rS(300 K)=18.0 cal/mol*K

+ Hydrogen = ( )

By formula: Fe⁺ + H₂ = (Fe⁺ H₂)

Quantity	Value	Units	Method	Reference	Comment
_rH°	12.5 ± 0.2	kcal/mol	SIDT	Bushnell, Kemper, et al., 1995	gas phase; «DELTA»_rH(0K) = 10.8 kcal/mol
Quantity	Value	Units	Method	Reference	Comment
_rS°	21.5	cal/mol*K	SIDT	Bushnell, Kemper, et al., 1995	gas phase; «DELTA»_rH(0K) = 10.8 kcal/mol

( Hydrogen ) + = ( 2)

By formula: (Fe⁺ H₂) + H₂ = (Fe⁺ 2H₂)

Quantity	Value	Units	Method	Reference	Comment
_rH°	17.0 ± 0.2	kcal/mol	SIDT	Bushnell, Kemper, et al., 1995	gas phase; «DELTA»_rH(0K) = 15.7 kcal/mol
Quantity	Value	Units	Method	Reference	Comment
_rS°	25.2	cal/mol*K	SIDT	Bushnell, Kemper, et al., 1995	gas phase; «DELTA»_rH(0K) = 15.7 kcal/mol

( 2 Hydrogen ) + = ( 3)

By formula: (Fe⁺ 2H₂) + H₂ = (Fe⁺ 3H₂)

Quantity	Value	Units	Method	Reference	Comment
_rH°	8.4 ± 0.1	kcal/mol	SIDT	Bushnell, Kemper, et al., 1995	gas phase; «DELTA»_rH(0K) = 7.5 kcal/mol
Quantity	Value	Units	Method	Reference	Comment
_rS°	19.1	cal/mol*K	SIDT	Bushnell, Kemper, et al., 1995	gas phase; «DELTA»_rH(0K) = 7.5 kcal/mol

( 3 Hydrogen ) + = ( 4)

By formula: (Fe⁺ 3H₂) + H₂ = (Fe⁺ 4H₂)

Quantity	Value	Units	Method	Reference	Comment
_rH°	9.7 ± 0.1	kcal/mol	SIDT	Bushnell, Kemper, et al., 1995	gas phase; «DELTA»_rH(0K) = 8.6 kcal/mol
Quantity	Value	Units	Method	Reference	Comment
_rS°	24.9	cal/mol*K	SIDT	Bushnell, Kemper, et al., 1995	gas phase; «DELTA»_rH(0K) = 8.6 kcal/mol

( 4 Hydrogen ) + = ( 5)

By formula: (Fe⁺ 4H₂) + H₂ = (Fe⁺ 5H₂)

Quantity	Value	Units	Method	Reference	Comment
_rH°	2.6 ± 0.1	kcal/mol	SIDT	Bushnell, Kemper, et al., 1995	gas phase; «DELTA»_rH(0K) = 2.2 kcal/mol
Quantity	Value	Units	Method	Reference	Comment
_rS°	17.9	cal/mol*K	SIDT	Bushnell, Kemper, et al., 1995	gas phase; «DELTA»_rH(0K) = 2.2 kcal/mol

( 5 Hydrogen ) + = ( 6)

By formula: (Fe⁺ 5H₂) + H₂ = (Fe⁺ 6H₂)

Quantity	Value	Units	Method	Reference	Comment
_rH°	2.7 ± 0.1	kcal/mol	SIDT	Bushnell, Kemper, et al., 1995	gas phase; «DELTA»_rH(0K) = 2.3 kcal/mol
Quantity	Value	Units	Method	Reference	Comment
_rS°	18.1	cal/mol*K	SIDT	Bushnell, Kemper, et al., 1995	gas phase; «DELTA»_rH(0K) = 2.3 kcal/mol

HN₂⁺ + Hydrogen = (HN₂⁺ )

By formula: HN₂⁺ + H₂ = (HN₂⁺ H₂)

Quantity	Value	Units	Method	Reference	Comment
_rH°	7.2	kcal/mol	PHPMS	Hiraoka, Saluja, et al., 1979	gas phase
Quantity	Value	Units	Method	Reference	Comment
_rS°	22.6	cal/mol*K	PHPMS	Hiraoka, Saluja, et al., 1979	gas phase

(HN₂⁺ Hydrogen ) + = (HN₂⁺ 2)

By formula: (HN₂⁺ H₂) + H₂ = (HN₂⁺ 2H₂)

Quantity	Value	Units	Method	Reference	Comment
_rH°	1.8	kcal/mol	PHPMS	Hiraoka, Saluja, et al., 1979	gas phase
Quantity	Value	Units	Method	Reference	Comment
_rS°	17.	cal/mol*K	PHPMS	Hiraoka, Saluja, et al., 1979	gas phase

+ Hydrogen = ( )

By formula: HO^- + H₂ = (HO^- H₂)

Quantity	Value	Units	Method	Reference	Comment
_rH°	7.	kcal/mol	CID	Paulson and Henchman, 1984	gas phase; approximate value

HO₂⁺ + Hydrogen = (HO₂⁺ )

By formula: HO₂⁺ + H₂ = (HO₂⁺ H₂)

Quantity	Value	Units	Method	Reference	Comment
_rH°	12.5	kcal/mol	PHPMS	Hiraoka, Saluja, et al., 1979	gas phase
Quantity	Value	Units	Method	Reference	Comment
_rS°	22.	cal/mol*K	PHPMS	Hiraoka, Saluja, et al., 1979	gas phase

(HO₂⁺ ) + Hydrogen = (HO₂⁺ )

By formula: (HO₂⁺ O₂) + H₂ = (HO₂⁺ H₂ O₂)

Quantity	Value	Units	Method	Reference	Comment
_rH°	4.0	kcal/mol	PHPMS	Hiraoka, Saluja, et al., 1979	gas phase
Quantity	Value	Units	Method	Reference	Comment
_rS°	17.	cal/mol*K	PHPMS	Hiraoka, Saluja, et al., 1979	gas phase

H₃⁺ + Hydrogen = (H₃⁺ )

By formula: H₃⁺ + H₂ = (H₃⁺ H₂)

Quantity	Value	Units	Method	Reference	Comment
_rH°	6.9 ± 0.4	kcal/mol	AVG	N/A	Average of 4 out of 11 values; Individual data points
Quantity	Value	Units	Method	Reference	Comment
_rS°	17.4 - 17.4	cal/mol*K	RNG	N/A	Range of 6 values; Individual data points

(H₃⁺ Hydrogen ) + = (H₃⁺ 2)

By formula: (H₃⁺ H₂) + H₂ = (H₃⁺ 2H₂)

Quantity	Value	Units	Method	Reference	Comment
_rH°	3.3 ± 0.2	kcal/mol	PHPMS	Hiraoka, 1987	gas phase
_rH°	3.1	kcal/mol	HPMS	Beuhler, Ehrenson, et al., 1983	gas phase
_rH°	3.4	kcal/mol	HPMS	Beuhler, Ehrenson, et al., 1983	gas phase; deuterated
_rH°	4.1	kcal/mol	PHPMS	Hiraoka and Kebarle, 1975	gas phase
_rH°	1.8	kcal/mol	HPMS	Bennett and Field, 1972	gas phase; Entropy change is questionable
Quantity	Value	Units	Method	Reference	Comment
_rS°	17.4	cal/mol*K	PHPMS	Hiraoka, 1987	gas phase
_rS°	16.9	cal/mol*K	HPMS	Beuhler, Ehrenson, et al., 1983	gas phase
_rS°	16.1	cal/mol*K	HPMS	Beuhler, Ehrenson, et al., 1983	gas phase; deuterated
_rS°	19.8	cal/mol*K	PHPMS	Hiraoka and Kebarle, 1975	gas phase
_rS°	10.8	cal/mol*K	HPMS	Bennett and Field, 1972	gas phase; Entropy change is questionable

(H₃⁺ 2 Hydrogen ) + = (H₃⁺ 3)

By formula: (H₃⁺ 2H₂) + H₂ = (H₃⁺ 3H₂)

Quantity	Value	Units	Method	Reference	Comment
_rH°	3.2 ± 0.1	kcal/mol	PHPMS	Hiraoka, 1987	gas phase
_rH°	3.8	kcal/mol	PHPMS	Hiraoka and Kebarle, 1975	gas phase
Quantity	Value	Units	Method	Reference	Comment
_rS°	18.5	cal/mol*K	PHPMS	Hiraoka, 1987	gas phase
_rS°	20.2	cal/mol*K	PHPMS	Hiraoka and Kebarle, 1975	gas phase

(H₃⁺ 3 Hydrogen ) + = (H₃⁺ 4)

By formula: (H₃⁺ 3H₂) + H₂ = (H₃⁺ 4H₂)

Quantity	Value	Units	Method	Reference	Comment
_rH°	1.7 ± 0.1	kcal/mol	PHPMS	Hiraoka, 1987	gas phase
_rH°	2.4	kcal/mol	PHPMS	Hiraoka and Kebarle, 1975	gas phase
Quantity	Value	Units	Method	Reference	Comment
_rS°	17.9	cal/mol*K	PHPMS	Hiraoka, 1987	gas phase
_rS°	19.3	cal/mol*K	PHPMS	Hiraoka and Kebarle, 1975	gas phase

(H₃⁺ 4 Hydrogen ) + = (H₃⁺ 5)

By formula: (H₃⁺ 4H₂) + H₂ = (H₃⁺ 5H₂)

Quantity	Value	Units	Method	Reference	Comment
_rH°	1.6 ± 0.1	kcal/mol	PHPMS	Hiraoka, 1987	gas phase
Quantity	Value	Units	Method	Reference	Comment
_rS°	18.9	cal/mol*K	PHPMS	Hiraoka, 1987	gas phase

(H₃⁺ 5 Hydrogen ) + = (H₃⁺ 6)

By formula: (H₃⁺ 5H₂) + H₂ = (H₃⁺ 6H₂)

Quantity	Value	Units	Method	Reference	Comment
_rH°	1.5 ± 0.1	kcal/mol	PHPMS	Hiraoka, 1987	gas phase
Quantity	Value	Units	Method	Reference	Comment
_rS°	20.0	cal/mol*K	PHPMS	Hiraoka, 1987	gas phase

(H₃⁺ 6 Hydrogen ) + = (H₃⁺ 7)

By formula: (H₃⁺ 6H₂) + H₂ = (H₃⁺ 7H₂)

Quantity	Value	Units	Method	Reference	Comment
_rH°	0.9 ± 0.1	kcal/mol	PHPMS	Hiraoka, 1987	gas phase
Quantity	Value	Units	Method	Reference	Comment
_rS°	16.5	cal/mol*K	PHPMS	Hiraoka, 1987	gas phase

(H₃⁺ 7 Hydrogen ) + = (H₃⁺ 8)

By formula: (H₃⁺ 7H₂) + H₂ = (H₃⁺ 8H₂)

Quantity	Value	Units	Method	Reference	Comment
_rH°	0.8 ± 0.1	kcal/mol	PHPMS	Hiraoka, 1987	gas phase
Quantity	Value	Units	Method	Reference	Comment
_rS°	17.9	cal/mol*K	PHPMS	Hiraoka, 1987	gas phase

(H₃⁺ 8 Hydrogen ) + = (H₃⁺ 9)

By formula: (H₃⁺ 8H₂) + H₂ = (H₃⁺ 9H₂)

Quantity	Value	Units	Method	Reference	Comment
_rH°	0.6 ± 0.1	kcal/mol	PHPMS	Hiraoka, 1987	gas phase
Quantity	Value	Units	Method	Reference	Comment
_rS°	19.1	cal/mol*K	PHPMS	Hiraoka, 1987	gas phase

+ Hydrogen = ( )

By formula: H₃O⁺ + H₂ = (H₃O⁺ H₂)

Quantity	Value	Units	Method	Reference	Comment
_rH°	3.5 ± 0.5	kcal/mol	SCATTERING	Okumura, Yeh, et al., 1990	gas phase

+ Hydrogen = ( )

By formula: K⁺ + H₂ = (K⁺ H₂)

Quantity	Value	Units	Method	Reference	Comment
_rH°	1.86	kcal/mol	SIDT	Bushnell, Kemper, et al., 1994	gas phase; «DELTA»_rH(0K) = 1.45 kcal/mol
Quantity	Value	Units	Method	Reference	Comment
_rS°	13.5	cal/mol*K	SIDT	Bushnell, Kemper, et al., 1994	gas phase; «DELTA»_rH(0K) = 1.45 kcal/mol

( Hydrogen ) + = ( 2)

By formula: (K⁺ H₂) + H₂ = (K⁺ 2H₂)

Quantity	Value	Units	Method	Reference	Comment
_rH°	1.47	kcal/mol	SIDT	Bushnell, Kemper, et al., 1994	gas phase; «DELTA»_rH(0K) = 1.35 kcal/mol
Quantity	Value	Units	Method	Reference	Comment
_rS°	11.2	cal/mol*K	SIDT	Bushnell, Kemper, et al., 1994	gas phase; «DELTA»_rH(0K) = 1.35 kcal/mol

+ Hydrogen = ( )

By formula: Li⁺ + H₂ = (Li⁺ H₂)

Quantity	Value	Units	Method	Reference	Comment
_rH°	6.5 ± 4.6	kcal/mol	EI	Wu, 1979	gas phase

+ Hydrogen = ( )

By formula: Na⁺ + H₂ = (Na⁺ H₂)

Quantity	Value	Units	Method	Reference	Comment
_rH°	2.93	kcal/mol	SIDT	Bushnell, Kemper, et al., 1994	gas phase; «DELTA»_rH(0K) = 2.45 kcal/mol
Quantity	Value	Units	Method	Reference	Comment
_rS°	13.2	cal/mol*K	SIDT	Bushnell, Kemper, et al., 1994	gas phase; «DELTA»_rH(0K) = 2.45 kcal/mol

( Hydrogen ) + = ( 2)

By formula: (Na⁺ H₂) + H₂ = (Na⁺ 2H₂)

Quantity	Value	Units	Method	Reference	Comment
_rH°	2.41	kcal/mol	SIDT	Bushnell, Kemper, et al., 1994	gas phase; «DELTA»_rH(0K) = 2.25 kcal/mol
Quantity	Value	Units	Method	Reference	Comment
_rS°	12.4	cal/mol*K	SIDT	Bushnell, Kemper, et al., 1994	gas phase; «DELTA»_rH(0K) = 2.25 kcal/mol

Mass spectrum (electron ionization)

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Data compiled by: NIST Mass Spectrometry Data Center, William E. Wallace, director

Spectrum

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Origin	American Petroleum Institute Research Project 44
NIST MS number	245692

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Constants of diatomic molecules

Go To: Top, Gas phase thermochemistry data, Phase change data, Reaction thermochemistry data, Henry's Law data, Gas phase ion energetics data, Ion clustering data, Mass spectrum (electron ionization), Site Links, NIST Free Links, References, Notes

Data compiled by: Klaus P. Huber and Gerhard H. Herzberg

Data collected through November, 1976

Symbols used in the table of constants
Symbol	Meaning
State	electronic state and / or symmetry symbol
T_e	minimum electronic energy (cm^-1)
ω_e	vibrational constant – first term (cm^-1)
ω_ex_e	vibrational constant – second term (cm^-1)
ω_ey_e	vibrational constant – third term (cm^-1)
B_e	rotational constant in equilibrium position (cm^-1)
α_e	rotational constant – first term (cm^-1)
γ_e	rotation-vibration interaction constant (cm^-1)
D_e	centrifugal distortion constant (cm^-1)
β_e	rotational constant – first term, centrifugal force (cm^-1)
r_e	internuclear distance (Å)
Trans.	observed transition(s) corresponding to electronic state
ν₀₀	position of 0-0 band (units noted in table)

Diatomic constants for H₂
State	T_e	_e	_ex_e	_ey_e	B_e	_e	_e	D_e	_e	r_e	Trans.	₀₀
WAVELENGTH TABLES of the H₂ spectrum from 2800 to 29000 Å with assignments of many of the lines Crosswhite, 1972. The TABLES OF ENERGY LEVELS Dieke, 1958 are also very useful as long as it is realized that the absolute values of the energy levels (n2) relative to the ground state need correction. Graphs and tables of POTENTIAL ENERGY CURVES for all known states of H₂, H₂⁺, and H₂^- Sharp, 1971.See note 1
Fragments of three other triplet systems. 2
u ³_u 6p	[123488.₀] 3				[29.3]			[0.023]		[1.06₉]	u a	26232.3 4
u ³_u 6p	↳Richardson, 1934; Dieke, 1958
t ³_u⁺ 5f	(121292) 5	(2661.4)	(121.9)		6						t a	(25342)
t ³_u⁺ 5f	↳Richardson, Yarrow, et al., 1934
q (³_g⁺) 5d	(121295) 5	[2172.6]			6						q c	(25325) 4
q (³_g⁺) 5d	↳Richardson, Yarrow, et al., 1934, 2
State	T_e	_e	_ex_e	_ey_e	B_e	_e	_e	D_e	_e	r_e	Trans.	₀₀
n ³_u 5p	120952.₉	2321.4	62.8₆		29.9₅	1.24 7		[0.023]		1.057	n a	24847.3 4
n ³_u 5p	↳Richardson, 1934; Dieke, 1958
m ³_u⁺ 4f	(119317) 8	[2457.1]			6						m a	23295.1 9
m ³_u⁺ 4f	↳Richardson, Yarrow, et al., 1934
s ³_g 4d	118875.₂	2291.7 10	62.4₄ 10		11						s c	22949.3 12
s ³_g 4d	↳Richardson, 1934; Foster and Richardson, 1953; Dieke, 1958
r ³_g 4d	118613.₇	2280.3 13	57.9₆ 13		11						r c	22683.2 13
r ³_g 4d	↳Richardson, 1934; Foster and Richardson, 1953; Dieke, 1958
State	T_e	_e	_ex_e	_ey_e	B_e	_e	_e	D_e	_e	r_e	Trans.	₀₀
p ³_g⁺ 4d	118509.₈	2303.1	76.9₀		6						p-k 14
	↳Miller and Freund, 1975
											p c	22586.0 4
	↳Richardson, 1934; Foster and Richardson, 1953; Dieke, 1958
v (³_g)	(118330) 15	2340	(57)		[(29.1)]					[(1.07₂)]	v c	(22430)
v (³_g)	↳Richardson, Yarrow, et al., 1934, 2
k ³_u 4p	118366.₂ 16	2344.37	67.2₉ 17	0.99	30.07₄	1.46₂ 18		[0.018₅]		1.054₇	k a	22271.0 4
k ³_u 4p	↳Richardson, 1934; Cunningham and Dieke, 1950; Dieke, 1958
State	T_e	_e	_ex_e	_ey_e	B_e	_e	_e	D_e	_e	r_e	Trans.	₀₀
f ³_u⁺ 4p	(116705)	[2143.6] 19			[27.0] 19					[1.11]	f a	20526.0 19
f ³_u⁺ 4p	↳Richardson, 1934; Dieke, 1958
o ³_u⁺	(114234) 20	2399.1	91.0		[35]					[0.98]	o a	(18160)
o ³_u⁺	↳Richardson, Yarrow, et al., 1934
l ³_u	113825 21	2596.8	106.0		[36]					[0.96]	l a	17846 4
l ³_u	↳Richardson, Yarrow, et al., 1934
j ³_g 3d	(113533)	2345.2₆ 22	66.5₆	0.745	30.08₅ 22	1.69₂		0.019₀		1.0545	j c 23 R	17633.0 24
j ³_g 3d	↳Richardson, 1934; Dieke, 1958
State	T_e	_e	_ex_e	_ey_e	B_e	_e	_e	D_e	_e	r_e	Trans.	₀₀
i ³_g 3d	(113132)	2253.5₅ 22	67.0₅ 25		29.22₁ 22	1.50₆		0.017₆		1.0700	i-d 26
	↳Freund and Miller, 1974
											i e R	5384.81 27
	↳Gloersen and Dieke, 1965
											i c 23 R	17185.8 24
	↳Richardson, 1934; Dieke, 1958
h ³_g⁺ 3s	(112913)	[2268.7₃] 28			[30.6₂] 28					1.045 1	h c	16990.8 29
h ³_g⁺ 3s	↳Richardson, Yarrow, et al., 1934, 3; Dieke, 1958
State	T_e	_e	_ex_e	_ey_e	B_e	_e	_e	D_e	_e	r_e	Trans.	₀₀
g ³_g⁺ 3d	112854.₄	2290.8₆	105.4₃ 30	2.403	31						g e R	5116.6
	↳Gloersen and Dieke, 1965
											g c 23	16917.6 29
	↳Richardson, 1934; Richardson, Yarrow, et al., 1934, 3; Dieke, 1958
d ³_u 3p	112700.₃ 32	2371.58 33	66.27	0.88	30.364 33 34	1.545		[1.91]		1.0496	d a 35 R	16619.0 29
d ³_u 3p	↳Dieke and Blue, 1935; Dieke, 1958
e ³_u⁺ 3p	107774.₇	2196.13	65.80	-0.433	27.30	1.515				1.107	e a R	11605.6
e ³_u⁺ 3p	↳Richardson, 1934; Dieke, 1935
State	T_e	_e	_ex_e	_ey_e	B_e	_e	_e	D_e	_e	r_e	Trans.	₀₀
a ³_g⁺ 2s	95936.₁ 36	2664.83	71.65 37	0.92	34.216	1.671		[0.0216]		0.9887₉	a b 38 39
a ³_g⁺ 2s											(a-X)	95076.4 36
c ³_u 3p	95838.₅ 40	2466.8₉	63.51	0.552	31.07 41 42	1.42₅		[0.019₅]		1.037₆	(c-X)	94881.₀ 43
b ³_u⁺²p	Unstable; lower state of the continuous spectrum of H₂ (a b). Pot. function Kolos and Wolniewicz, 1965.
Several excited states above the ionization limit, established by electron impact studies and leading to two exited atoms or H + H⁺.
Continuous absorption above ~130000 cm^-1. 44
v'=0 Rydberg series of rotational levels observed in low temperature absorption from X ¹_g⁺, v"=0, J"=0 and 1 and converging to:
Rydberg	N=2 of H₂⁺: J=1 levels of np ¹_u⁺ (n=6,...,32, joining on to C, D, D', D")45; = 124591.5 46 - R/(n + 0.082)². Similar series with v'=1,...,6 47. R(0) lines (para H₂)
	↳Herzberg, 1969; Takezawa, 1970, 2; missing citation
	N=1 of H₂⁺: J=1 levels of np ¹_u^- (n=6,...,43, joining on to C, D, D', D")48; = 124476.0 46 - R/(n + 0.082)². Similar series with v'=1,...,5. Q(1) lines (ortho H₂)
	↳Herzberg, 1969; Takezawa, 1970, 2; missing citation
	N=1 of H₂⁺: J=0 levels of np ¹_u⁺ (n=5,...,19, joining on to B, B', B")48; = 124476.0 46 - R/(n + 0.203)². Similar series with v'=1,2,3. P(1) lines (ortho H₂)
	↳Takezawa, 1970, 2; missing citation
	N=0 of H₂⁺: J=1 levels of np ¹_u⁺ (n=5,...,40, joining on to B, B', B")45; = 124417.0 46 - R/(n + 0.203)². Similar series with v'=1,...,6. 5 R(0) lines (para H₂)
	↳Herzberg, 1969; Takezawa, 1970, 2; missing citation
B bar ¹_u⁺	State causing ion-pair formation after excitation of higher Rydberg states; also responsible for perturbations in B' ¹_u⁺. Correlates at small r with B" ¹_u⁺, forming a double-minimum state.
B bar ¹_u⁺	↳Dabrowski and Herzberg, 1974; Chupka, Dehmer, et al., 1975; Kolos, 1976
State	T_e	_e	_ex_e	_ey_e	B_e	_e	_e	D_e	_e	r_e	Trans.	₀₀
D" ¹_u 5p	121211.0 49	2319.92 49	63.041		30.7₆ 50 51	1.45 50		(0.03)		1.043	D" X R	120176.0 49
D" ¹_u 5p	↳Monfils, 1965; Monfils, 1968
D' ¹_u 4p	118865.3 49	2329.97 49	63.140		29.8₉ 52 51	1.11 52	-0.53	[0.025] 52		[(1.058)]	D' X R	117835.2 49
D' ¹_u 4p	↳Namioka, 1964; Monfils, 1965; Monfils, 1968
S ¹_g 4d	[119893] 53 3				[(28.8)] 54					[(1.07₈)]	S B V	27510
S ¹_g 4d	↳Richardson, 1934; Dieke, 1958
O ¹⁺ 4s	[(119870)] 55 3				[(32)]					[(1.0₂)]	O B V	(27487) 56
O ¹⁺ 4s	↳Richardson, 1934
State	T_e	_e	_ex_e	_ey_e	B_e	_e	_e	D_e	_e	r_e	Trans.	₀₀
R ¹_g 4d	(118688) 57	[2142] 58			[(30)] 54					[(1.0₆)]	(R C)	(18488)
	↳Richardson, 1934; Dieke, 1958
											R B V	27376 45
	↳Richardson, 1934; Dieke, 1958
P ¹_g⁺ 4d	[119531] 59 3				[(30)] 54					[(1.0₆)]	(P C)	18260 49
	↳Richardson, 1934; Dieke, 1958
											P B V	27148 60
	↳Richardson, 1934; Dieke, 1958
State	T_e	_e	_ex_e	_ey_e	B_e	_e	_e	D_e	_e	r_e	Trans.	₀₀
T ¹⁺	[119512.6] 61 3				[(25.4)]					[(1.14₈)]	T B V	27130.1
T ¹⁺	↳Richardson, 1934; Dieke, 1958
B" ¹_u⁺ 4p	117984.5	2197.5	68.136		26.68 62 63	1.19 62		[0.034]		[(1.119₈)]	B" X R	116886.9 64
B" ¹_u⁺ 4p	↳missing citation; Monfils, 1965; Monfils, 1968; missing citation
N ¹_g⁺	(116287) 65	[1983.3]			[(18.4)]					[(1.35)]	N B R	24896.4
N ¹_g⁺	↳Richardson, 1934; Dieke, 1958
U (¹_g⁺)	[116707.7] 65 66				[(18.8)]					[(1.33)]	U B 67 R	24325.1
U (¹_g⁺)	↳Richardson, 1934; Dieke, 1958
State	T_e	_e	_ex_e	_ey_e	B_e	_e	_e	D_e	_e	r_e	Trans.	₀₀
M ¹_g⁺	(114485) 65	[2176.0]			[(13)]					[(1.6₀)]	M B R	23190.0 68
M ¹_g⁺	↳Richardson, 1934; Dieke, 1958
L ¹_g⁺	(114520) 65	[(1835)]			[(9.7)]					[(1.8₆)]	L B R	23054.8
L ¹_g⁺	↳Richardson, 1934; Dieke, 1958
H ¹_g⁺ 3s	113899 69	2538	124		[(29.5)]					[(1.06₅)]	H C R	13866.6
	↳Richardson, 1934; Dieke, 1958
											H B V	22754.1 70
	↳Richardson, 1934; Dieke, 1958
State	T_e	_e	_ex_e	_ey_e	B_e	_e	_e	D_e	_e	r_e	Trans.	₀₀
D ¹_u 3p	113888.7	2359.91	68.81₆ 71		30.29₆ 72 73 63	1.42 72		0.0201 74		1.0508	D E R	13709.₇
	↳Richardson, 1937; Dieke, 1958
											D X 75 R	112872.3 76
	↳missing citation; Monfils, 1965; Monfils, 1968; missing citation
J ¹_g 3d	(113550)	2341.1₅ 77	63.2₃ 77		30.08₁ 77	1.71₈ 77		0.018₉ 77		1.0546	J C 78 R	13435.6 79
	↳Richardson, 1934; Dieke, 1958
											J B 78 V	22322.5 79
	↳Richardson, 1934; Dieke, 1958
State	T_e	_e	_ex_e	_ey_e	B_e	_e	_e	D_e	_e	r_e	Trans.	₀₀
I ¹_g 3d	(113142) 80	2259.1₅ 77	78.4₁ 77 80		29.25₉ 77 81	1.58₄ 77		0.018₀ 77		1.0693	I C 81 R	12982.5 82
	↳Richardson, 1934; Dieke and Lewis, 1937; Dieke, 1958
											I B V	21869.5 82
	↳Richardson, 1934; Dieke and Lewis, 1937; Dieke, 1958
G ¹_g⁺ 3d	112834 83	2343.9	55.9 84		[(28.4)] 85					[(1.08₅)]	G C 86 85 R	12722.2 87
	↳Richardson, 1934; Dieke, 1958
											G B 86 V	21609.2 87
	↳Richardson, 1934; Dieke, 1958
State	T_e	_e	_ex_e	_ey_e	B_e	_e	_e	D_e	_e	r_e	Trans.	₀₀
K (¹_g⁺)	(112669) 88	[2232.59]	30		[10.8]					[1.76]	K C R	12538.6
	↳Richardson, 1934; Dieke, 1958
											K B R	21425.4
	↳Richardson, 1934; Dieke, 1958
Q (¹_g)	(113163) 89	[742]			[(16.3)]					1.43	Q B R	21151.₁
Q (¹_g)	↳Richardson, Yarrow, et al., 1934; Dieke, 1958
B' ¹_u⁺ 3p	111642.₈ 90	2039.52	83.406 91		26.70₅ 92	2.781 93		[0.012] 94		1.119₂	B' E,F 95	11311.5 96
	↳Porto and Jannuzzi, 1963
											B' X 97 R	110478.2
	↳Namioka, 1964; Namioka, 1965; Monfils, 1965
State	T_e	_e	_ex_e	_ey_e	B_e	_e	_e	D_e	_e	r_e	Trans.	₀₀
F ¹_g⁺ 2p²	100911 98 99	[1199] 98		100			101				F B 102 R 103
F ¹_g⁺ 2p²	↳Dieke, 1949; Porto and Jannuzzi, 1963
E ¹_g⁺ 2s	100082.3 98 104	2588.9 104	130.5 104		32.68 104	1.818 104		[0.0228] 104		1.011₈	E B 102 V	8961.23
E ¹_g⁺ 2s	↳Dieke, 1936; Porto and Dieke, 1955; Dieke, 1958; Porto and Jannuzzi, 1963
C ¹_u 2p	100089.8 95	2443.77	69.524 105 106		31.362₉ 106	1.664₇ 107		0.0223	-0.0007₄	1.0327₉	C X 108 109 R	99120.1₇ 95
C ¹_u 2p	↳Dieke, 1938; Namioka, 1964, 2; Namioka, 1965; Dabrowski and Herzberg, 1974
B ¹_u⁺ 2p	91700.0 110	1358.09	20.888 111		20.015₄ 112	1.1845 113		0.01625 114		1.2928₂	B X 115 116 117 R	90203.3₅
B ¹_u⁺ 2p	↳Herzberg and Howe, 1959; Wilkinson, 1968; Dabrowski and Herzberg, 1974
State	T_e	_e	_ex_e	_ey_e	B_e	_e	_e	D_e	_e	r_e	Trans.	₀₀
X ¹_g1s²	0	4401.21₃	121.33₆ 118		60.853₀ 119	3.062₂ 120		0.0471 121		0.74144 122
	↳Herzberg, 1950; Fink, Wiggins, et al., 1965; Terhune and Peters, 1959; Foltz, Rank, et al., 1966; Brannon, Church, et al., 1968
	Raman sp. 123
	↳Stoicheff, 1957; Foltz, Rank, et al., 1966
	Rotational 124 and nuclear rf magn. Reson.
	↳Harrick and Ramsey, 1952; Barnes, Bray, et al., 1954; Kolsky, Phipps, et al., 1952; Harrick, Barnes, et al., 1953

Notes

The T_e values for the upper states of the triplet transitions are based on T_e" for the lower state (a or c) and have been calculated assuming Y'₀₀ ~ Y"₀₀.

³B

c, ³C

c, 7p

a Richardson, 1934, Richardson, Yarrow, et al., 1934, 2.

Only v=0 observed.

Referred to the (non-existent) N=0 level in ³

states; the N=1 levels of c ³

(+ and -) lie 60.7 cm^-1 above N=0.

t and q are designated ³F and ³G, respectively, in Richardson, Yarrow, et al., 1934, 2, Richardson, Yarrow, et al., 1934.

The states g ³ Sigma

_g⁺(3d

), p ³

_g⁺(4d

), q ³

_g⁺(5d

), m ³

_u⁺(4f

) and t ³

_u⁺(5f

) are strongly affected by l-uncoupling. The N=1 levels lie below N=0 for v=0 and 1; meaningful B values cannot be given until the whole d and f complexes have been fully analyzed, see Ginter, 1967.

Represents B₀ and B₁ of ³

^- only; B₂ = 26.26 Richardson, Yarrow, et al., 1934, B₃ = 24.54 Richardson, Yarrow, et al., 1934.

³E of Richardson, Yarrow, et al., 1934.

Refers to N'=0 which lies above N'=4 because of strong l-uncoupling.

Constants refer to N=2; from v= 0,1,2.

Because of strong l-uncoupling no meaningful B values can be given; see 6.

Refers to the N=2 level of s ³ Delta

_g^- above the hypothetical level N=0 of c ³

_u; see 4.

The constants refer to N=1 of r ³

_g^-;

₀₀ is the energy above the hypothetical level N=0 of c(v=0), see 4.

Anticrossings and microwave transitions. The energy difference between k ³

_u(v=1,N=3) and p ³ Sigma

_g⁺(v=1,N=5) is +0.2785 cm^-1. Fine structure parameters.

³A of Richardson, Yarrow, et al., 1934, 2; probably a doubly excited state. The possibility (1s sigma

)(4f

) mentioned by Richardson, Yarrow, et al., 1934, 2 and quoted in MOLSPEC 1 can be ruled out since it does not give rise to an even state.

A₀(ortho)= -0.00937 Freund, Miller, et al., 1973, Miller, Freund, et al., 1974, Miller and Freund, 1975, A₀(para)= -0.0071₀ cm^-1 Freund, Miller, et al., 1973, Miller, Freund, et al., 1974, Miller and Freund, 1975; also hyperfine structure investigated by these authors.

_ey_e= +0.99 Cunningham and Dieke, 1950.

From B₀ and B₁ of

^- only Richardson, 1934.

Calculated from the data in Richardson, 1934 and Dieke, 1958. Delta

G(1/2) and

₀₀ refer to actual N=0 level which is strongly perturbed.

³D of Richardson, Yarrow, et al., 1934. Probably a doubly excited state: (2p sigma

)(3d

³Y of Richardson, Yarrow, et al., 1934. Probably a doubly excited state: (2p sigma

)(3d

These constants [from Ginter, 1967] refer to the ³

^- and ³

^- components and are based on "Approximation 2" of Ginter, 1966 for the evaluation of the l-uncoupling. The observed levels are given by Dieke, 1958.

Observed in absorption in flash discharges Herzberg, 1967.

Lower component of N'=l (i ³

) or 2 (J ³ Delta

) relative to the (non-existent) N"=0 level of c ³

Ab initio calculations Browne, 1965, Wright and Davidson, 1965 give a pronounced potential maximum near 2.5 Å for this state.

Anticrossings and microwave transitions; i ³

_g(v=3,N=2) is 1.9244 cm^-1 above d ³

_g(v=3,N=1).

Refers to

^-(N=1).

⁺(N=1) is at 5471.70 cm^-1 above e ³ Sigma

_u⁺(v=0,N=0). The rotational levels are very irregular, only partly on account of l-uncoupling.

From Dieke, 1958. omega

_e = 2395.2 Richardson, Yarrow, et al., 1934, 3, omega

_ex_e = 64.2 Richardson, Yarrow, et al., 1934, 3, B₀ = 30.0 Richardson, Yarrow, et al., 1934, 3. According to Dieke, 1958 the v=0 levels may be spurious. If so, only v=1 remains with B₁ = 28.7₂.

Referred to the (non-existent) N=0 level in ³

states; the N=1 levels of c ³

(+ and -) lie 60.7 cm^-1 above N=0.

Calculated from the N=0 levels of Dieke, 1958.

The states g ³ Sigma

_g⁺ (3d

), p ³

_g⁺ (4d

), q ³

_g⁺ (5d

), m ³

_u⁺ (4f

) and t ³

_u⁺ (5f

) are strongly affected by l-uncoupling. The N=1 levels lie below N=0 for v=0 and 1; meaningful B values cannot be given until the whole d and f complexes have been fully analyzed, see Ginter, 1967.

The fine structure in the N=1 levels of both ortho- and para-H₂ has been observed in microwave-optical double resonance by Freund and Miller, 1973 who give A_e = 0.0281 Freund and Miller, 1973 as well as spin-spin coupling constants. For para-H₂, v=0, N=1, the three component levels J=1,2, and 0 are at -0.01241, -0.00695, and +0.07197 cm^-1, respectively. For ortho-H₂ the hyperfine structure has also been studied.

Constants refer to ³

^-. ³

⁺ is strongly perturbed, i.e. the Lambda

- type doubling is fairly large and irregular Dieke, 1935, 2.

Breaking-off of P and R branches (³

⁺) above v'=3 on account of predissociation. Breaking-off of Q branches (³

^-) for v'=7,8 above N=1 on account of preionization Beutler and Junger, 1936, 2.

Lifetime

=63 ns Cahill, 1969; see, however, Marechal, Jost, et al., 1972 who give tau

= 31 ns Marechal, Jost, et al., 1972.

The T₀(

₀₀) value is derived from singlet-triplet anti-crossings in a magnetic field Miller and Freund, 1974, Jost and Lombardi, 1974 and corresponds to v=0, N=0. It agrees fairly well with 95073.₂ obtained from the energy of a ³ Sigma

_u⁺(v=0,N=0) below the ionization limit, 29344 ± 2 cm^-1 Beutler and Junger, 1936, 2, combined with the new value of I.P.(H₂). Dieke, 1958 gives T₀ = 95226 without explanation; the most recent theoretical value is T₀= 95077.3 Kolos, 1975. The T_e value in the table takes account of Y₀₀ in both upper (Y'₀₀= 4.9₂) and lower state.

_ey_e= +0.92. Precise ab initio potential function (including diagonal corrections) and predicted vibrational levels in Kolos and Wolniewicz, 1968. Except for a constant shift, the latter agree well with the observed levels Dieke, 1958.

Lifetime

(v=0,1) = 10.4₅ ns Smith and Chevalier, 1972, King, Read, et al., 1975.

Reproduction in MOLSPEC 1, Fig.l2.

A = -0.1249 cm^-1 Jette, 1974, Jette and Miller, 1974. T_e takes account of Y₀₀ in both upper (Y'₀₀= 4.1₈) and lower state.

The

-type doubling is quite small (~ 0.5 cm^-1 for N=6); the constants refer to the average. The triplet splitting in N=2 of para-H₂ has been fully resolved in molecular beam experiments of Lichten, 1960 yielding Delta

(J=2-1) = 0.16438 Lichten, 1960, Delta

(J=2-3) = 0.19674 cm^-1 Lichten, 1960 with J=2 at the top. The hyperfine structure in N=1,J=2 of ortho-H₂ is Delta

(F=3-2) = 0.0236 Frey and Mizushima, 1962, Delta

(F=2-1) = 0.0154 cm^-1 Frey and Mizushima, 1962 as quoted by Frey and Mizushima, 1962. Foster and Richardson, 1953 give spin splittings for N = 1,2,3,4,5 without resolving J=N+l from J=N-1.

The levels of c ³

_u⁺ are strongly predissociated by the b ³ Sigma

_u⁺ state Herzberg, 1967; the levels of c ³

_u^- are either very weakly affected by a forbidden predissociation to b ³ Sigma

_u⁺ Lichten, 1962, Chiu, 1964 or decay radiatively (by magnetic dipole radiation) to the b ³ Sigma

_u⁺ state as suggested by the lifetime measurements of Johnson, 1972, tau

(v=0)= 1.02 ms Johnson, 1972 independent of spin component and isotope. Johnson, 1974 observed quenching of c ³

_u^- in an electric field. The Stark effect is large (~ E+4 times greater than for the ground state) and has been studied experimentally by Kagann and English, 1976 and compared with the theoretical values of English and Albritton, 1975.

This number, obtained from

₀₀(a-X) +

₀₀(e-a) +

₀₀(g-e) -

₀₀(g-c), is 87 cm^-1 higher than given in MOLSPEC 1, a change made necessary by the work of Gloersen and Dieke, 1965. See also 36.

Theoretical and experimental values for the ionization probability into the various vibrational levels of H₂⁺ are given by Dunn, 1966, Villarejo, 1968, 2, Nicholls, 1968, Ford, Docken, et al., 1975 and Villarejo, 1968, Turner, 1968, respectively. The ionization cross section near the ionization limit has been studied at high resolution by Chupka and Berkowitz, 1968, Comes and Wellern, 1968. See also Backx, Wight, et al., 1976.

For high n there is strong l-uncoupling and the two series of ¹ Sigma

_u⁺ and ¹

_u⁺ levels of para-H₂ should be called np0 and np2, respectively, corresponding to the fact that the first converges to N=0, the second to N=2 of H₂⁺ There are strong systematic perturbations between the J=1 levels of these two series (because of l- uncoupling) so that the formulae as given do not represent the series very well. An accurate representation can be obtained by Fano's quantum defect theory; see Herzberg and Jungen, 1972. Levels of np

, ¹

_u⁺ above N=0 of H₂⁺ are preionized resulting in asymmetrically broadened absorption lines with apparent emission wings.

Limits of Rydberg series above v"=0, J"=0.

Chupka, Dehmer, et al., 1975 have observed Rydberg levels with v = 9,10,11 in the study of ion-pair formation.

These two series of ortho levels are essentially unperturbed.

Average of

⁺ and

^-.

₀₀ referred to (N'=0).

Refers to

^-;

⁺ is perturbed; B₀(

⁺) = 30.178, B₁(

⁺) = 31.370.

RKR potential function in Monfils, 1968, 2.

Refers to

^-;

_e = -0.53.

⁺ is perturbed, B₀(

⁺) = 31.09₅, B₁(

⁺) = 29.165.

4F of Dieke, 1958, 4¹ chi

of Richardson, 1934.

The states P,R,S form a d complex with strong uncoupling. As a result the constants given have only limited meaning.

4¹O of Richardson, 1934, not given by Dieke, 1958.

From R(0) and P(1) according to the data of Richardson, 1934.

4¹B of Richardson, 1934, 4E of Dieke, 1958.

Refers to ¹

^-.

4¹C of Richardson, 1934, 4D of Dieke, 1958.

The J=1 level is observed at 27207.62 cm^-1 above J=0, v=0 of B ¹ Sigma

_u⁺. The value given for J=0 is extrapolated and, because of the uncoupling, is rather uncertain.

4¹K of Richardson, 1934, doubly excited state.

Representing only B₀ and B₁. The B_v curve has a positive curvature for low v and a strong negative curvature for high v. B_v = 27.1₃ - 2.35(v+1/2) + 0.665(v+1/2)² - 0.0729(v+1/2)³ Monfils, 1965.

RKR potential function Monfils, 1968, 2. Ab initio potential function Kolos, 1976.

Deperturbed value from Namioka, 1964. The observed value for J=0 [perturbed by B'(v=4)] is 116885.6 according to Namioka, 1964 and 116885.3 according to Monfils, 1965, while in the more recent paper Monfils, 1968 gives 116882.00.

All these states are considered as doubly excited states by Dieke, 1958. They may well form one or two double-minimum states (similar to E, F) together with H ¹ Sigma

_g⁺.

Only v=0.

This is the lambda

4142.8 progression of Richardson, 1934 as revised by Dieke, 1958.

These values agree with Dieke, 1958; Richardson, 1934 gives 23057.22 and 23191.66 for L and M, respectively.

3¹0 of Richardson, 1934.

From R(0) of the 0-0 band and F(1)-F(0) as given by Richardson, 1934. The basis for 22751.6 in Richardson, 1934 is not clear.

_ex_e= +1.027₄(v+1/2)³ - 0.0420₂(v+1/2)⁴; the vibrational constants Monfils, 1968 refer to the average of

⁺ and

^-. See also 73.

The rotational constants Namioka, 1964 represent only the levels v= 0, 1, 2 of

^-. The

⁺ levels are strongly perturbed by the B' state which also causes the predissociation of ¹

⁺ for v'

3; see 73. Monfils, 1965 gives for the deperturbed values: B_v(

⁺)= 32.5₁- 2.00(v+1/2) + 0.071(v+1/2)² - 0.0040(v+1/2)³ ; B_v(

^-)= 30.8₁ - 1.96(v+1/2) + 0.102(v+1/2)² - 0.0053(v+1/2)³ .

Strong predissociation for v' geq

3; no bands with v' geq

3 have ever been observed in emission. In absorption strongly broadened lines with apparent emission wings (Beutler- Fano shapes) in D ¹

_u^-

X ¹

_g^- Herzberg, 1971; line widths of 4 and 11.5 cm^-1 for J=1 and 2, respectively, have been observed Comes and Schumpe, 1971 and accounted for by interaction with the continuum of B' ¹ Sigma

_u^- Fiquet-Fayard and Gallais, 1971, Julienne, 1971, Fiquet-Fayard and Gallais, 1972. Widths for D ¹

_u^-

X ¹

_g^- (Q) lines are much smaller. Ly alpha

fluorescence as a result of predissociation Comes and Wellern, 1968, Comes and Wenning, 1969, Mentall and Gentieu, 1970. Electric field induced component of predissociation Comes and Wenning, 1970.

From Namioka, 1964; Monfils, 1965 gives D_v(

⁺) = 0.033+0.0010(v+1/2) Monfils, 1965, D_v(

^-) =0.0283 - 0.0012(v+1/2) Monfils, 1965.

RKR Franck-Condon factors Spindler, 1969. Absorption coefficients of D larrow

X bands Cook and Metzger, 1964. 0scillator strengths f₀₀ = 0.0061₄ Lewis, 1974, f₂₀ = 0.010₉ Lewis, 1974.

Average of

⁺ and

^- extrapolated to J=0. The Lambda

-type doubling for v=0, J=1 is 4.2 cm^-1 with

⁺ above

^-.

These constants Ginter, 1967 refer to

^- and

^- and take into account the effects of l- uncoupling in the d-complex according to the formulae of Ginter, 1966. They cannot be used to derive energy levels without the use of these formulae. The observed levels are given in Dieke, 1958.

The forbidden ¹ Delta

_u^- transition occurs because of strong uncoupling in the upper state. Only Q branches are observed in these bands.

Refers to J=2 of Delta

^- at 10.8 cm^-1 below J=2 of Delta

⁺.

3¹B of Richardson, 1934, 3E of Dieke, 1958. Mulliken, 1964 and Browne, 1965 predict a fairly high (0.4 eV) maximum in the potential function of this state.

Zeeman effect studies Dieke, Cunningham, et al., 1953 yield g(v=0,J=1) = 0.49₈ Dieke, Cunningham, et al., 1953, g(v=0,J=2) = 0.412 Dieke, Cunningham, et al., 1953, etc.; lifetime tau

(v=0,J=2) = 38 ns van der Linde and Dalby, 1972, see 85.

Referred to J'=1 of I ¹

^-; J=1 of I ¹

⁺ is 62.32 cm^-1 higher.

3¹C of Richardson, 1934, 3D of Dieke, 1958.

No levels higher than v=3 have been observed which suggests that the dissociation limit is 1²S + 2²S,²P at 118377.6 cm^-1. The constants represent only v=0,1,2.

This value Richardson, 1934 does not represent the low rotational levels because of l-uncoupling, e.g. the J=1 level is below J=0. The actual levels are given in Dieke, 1958. Hyperfine structure for v=1,J=1; A = 1.0 ± 0.17 MHz Melieres-Marechal and Lombardi, 1974. Large Zeeman splittings corresponding to the strong l-uncoupling Dieke, Cunningham, et al., 1953, g(v=0,J=1) = 0.901 Dieke, Cunningham, et al., 1953, g(v=0,J=2) = 0.571 Dieke, Cunningham, et al., 1953, etc.; see also Freund and Miller, 1972. Lifetimes from Hanle effect observations van der Linde and Dalby, 1972; tau

(v=0,J=1) = 27 ns van der Linde and Dalby, 1972, tau

(v=0,J=2,3) = 39 ns van der Linde and Dalby, 1972.

The G

B system gives rise to the strongest lines in the visible region.

Referred to J'=0 which, because of l-uncoupling, has an anomalous position.

3¹K of Richardson, 1934, probably due to (2s sigma

)².

Fragmentary, possibly (2p sigma

)(2p

Takes account of Y₀₀ in both upper and lower state. Y'₀₀ = 15.3 cm^-1 is rather uncertain and depends strongly on the number of levels included. See 93.

_ex_e= +3.533(v+1/2)³ - 0.93750(v+1/2)⁴; these are the constants of Namioka, 1964 [except T_e which is taken from Dabrowski and Herzberg, 1974], they apply only to v=0,...,4. Monfils, 1968 gives a very different set of constants based on seven levels v=0,...,6. The Delta

G curve (in H₂, HD, and D₂) has a characteristic tail which makes representation of the higher vibrational levels by a conventional formula meaningless Namioka, 1964, Dabrowski and Herzberg, 1974.

RKR potential functions Namioka, 1965, Monfils, 1968, 2. A very slight maximum of the potential function at 2.9 Angstroms has been predicted by Ford, Browne, et al., 1975 but not confirmed in the calculations of Kolos, 1976; see also Wolniewicz, 1975. The experimental data, while suggesting an anomalous form of the potential function, do not indicate a maximum Dabrowski and Herzberg, 1974.

a_v= +0.540(v+1/2)² - 0.091₇(v+1/2)³; these constants Namioka, 1964 represent only the first five (deperturbed) B_v values. If only three levels are used B_v= 26.371- 1.9000(v+1/2)-0.0050(v+1/2)² leading to a very different Y₀₀ value (3.6) from the one used here (see 90).

The higher D_v values are quite irregular.

The T_e values for B and C include the effects of Y₀₀ on the zero point energies in both upper and lower states; Y'₀₀(B) = 8.7, Y'₀₀(C) = 5.0 cm^-1. On the other hand, the T_e value of C ¹

_u and

₀₀(C-X) exclude the term - B Lambda

² in the energy formula, a term that is usually included to form part of the effective potential energy. With this inclusion and disregarding Y₀₀ Namioka, 1965 gives T_e = 100063.42 and

₀₀ = 99090.35 on the basis of older data for v=0...4 and his own precise data for v=5....13.

From the 0-1 band of Porto and Jannuzzi, 1963; from T₀(B')-T₀(E) one obtains 11313.6₂.

RKR Franck-Condon factors Spindler, 1969. Oscillator strengths f₁₀ = 0.0028 Lewis, 1974, f₃₀ = 0.0048 Lewis, 1974.

Because of strong interaction the two states E [2¹X of Richardson, 1934, 2A of Dieke, 1958] and F, in zero approximation ls sigma

and (2p

)², form a single state with two minima as first recognized by Davidson, 1961. The most detailed calculation of the potential function and the energy levels is that of Kolos and Wolniewicz, 1969 whose numbering and Delta

G(1/2) value for the F ¹ Sigma

_g^- component has been adopted in the table. According to Kolos and Wolniewicz, 1969

₀₀(F-B) would be at 9146.8 cm^-1 but v=0,1,2,3 of F have not been observed. The observed v=4 level lies just below the potential maximum.

From the observed

₄₀ and the energy of v=4 above the (outer) minimum as calculated by Kolos and Wolniewicz, 1969.

100

B₄ = 6.24 129

101

R₄=2.31₅ 129

102

Franck-Condon factors Lin, 1974. Electronic transition moment Wolniewicz, 1969.

103

₄₀ =13635.1

104

These numbers represent only the lower vibrational levels near the inner minimum. Owing to the interaction of E and F (see 98) higher Delta

G(v+1/2), B_v, D_v values are irregular.

105

_ex_e= +0.73l2(v+1/2)³ - 0.04l5(v+1/2)⁴. These constants refer to the (unperturbed)

^- component and are based on an 8-level fit to the data of Dabrowski and Herzberg, 1974 [v=0-4] and Namioka, 1964, 2 [v=5-7]. Somewhat different constants are given by Namioka, 1965. Note, that the T_e values in Dieke, 1958 are too low by 8.4 cm^-1 Namioka, 1965. The constants of Monfils, 1968 are affected by not recognizing this error.

106

Theoretical work King and Van Vleck, 1939, Mulliken, 1960, Kolos and Wolniewicz, 1965, Rothenberg and Davidson, 1966, Kolos, 1967 has predicted, and the analysis of the spectrum Namioka, 1964, Dabrowski and Herzberg, 1974 has confirmed, that the potential curve of C ¹

_u has a van der Waals maximum of ~ 105 cm^-1 above the asymptote near r=4.8 Angstroms. ab initio potential function (without diagonal corrections) and predicted vibrational levels Kolos and Wolniewicz, 1968. RKR potential functions Namioka, 1965 Monfils, 1968, 2; see, however, Julienne, 1973.

107

_v= +0.0296(v+1/2)² - 0.00296(v+1/2)³. These constants refer to the

^- component (

⁺ is strongly perturbed by B ¹ Sigma

_u^-) and are from an 8-level least- squares fit of the data of Dabrowski and Herzberg, 1974 [v = 0-4] and Namioka, 1964, 2 [v=5-7]. Somewhat discordant B_v values for both

^- and

⁺ (the latter after deperturbation) are given by Namioka, 1964, 2, Monfils, 1965, Dabrowski and Herzberg, 1974. The Lambda

-type doubling for v=0, J-l is 1.17 cm^-1; for other v, J as well as theoretical values see Julienne, 1973, Ford, 1974.

108

Lifetime

(v=0,1,2,3) = 0.6 ns Hesser, 1968.

109

RKR Franck-Condon factors calculated by missing citation,89 and "measured" by Geiger and Schmoranzer, 1969, Schmoranzer and Geiger, 1973, Fabian and Lewis, 1974 who have also determined the dependence of the transition moment on r. Ab initio calculation of the latter by Wolniewicz, 1969. Theoretical transition probabilities and f values Wolniewicz, 1969, Allison and Dalgarno, 1970, Allison and Dalgarno, 1970, 2, Dalgarno and Stephens, 1970, experimental values Hesser, 1968, Fabian and Lewis, 1974, Lewis, 1974: f₁₀ = 0.059, f₂₀ = 0.060, f₃₀ = 0.044,... Calculated transitions to the continuum of X ¹ Sigma

_g^- Stephens and Dalgarno, 1972. Selective enhancements of v=0 and 2 of C ¹

_u in Ar-H₂ mixtures have been studied by Takezawa, Innes, et al., 1966; similar enhancements have also been observed in Kr-H₂ mixtures. For stimulated emission in the Q(1) and P(3) lines of the 1-4, 2-5, 2-6, 3-7 Werner bands see Hodson and Dreyfus, 1972, Waynant, 1972.

110

_u and

₀₀(C-X) exclude the term - B Lambda

₂ in the energy formula, a term that is usually included to form part of the effective potential energy. With this inclusion and disregarding Y₀₀ Namioka, 1965 gives T_e = 100063.42 and

₀₀ = 99090.35 on the basis of older data for v=0...4 and his own precise data for v=5....13.

111

_ex_e= +0.7196(v+1/2)³ - 0.0598(v+1/2)⁴ +0.002l6(v+1/2)⁵, Y₀₀ = 8.7; from a least squares fit Dabrowski and Herzberg, 1974 to the first eight levels as given by Herzberg and Howe, 1959. Wilkinson, 1968 gives slightly different constants based on the first five levels only. Monfils, 1968 and Namioka, 1964, 2 have observed levels up to v= 35 and 37, respectively, very close to the dissociation limit at 118377.₆ cm^-1 Herzberg, 1970. The dissociation energy of the B ¹ Sigma

_u^- state is 28174.2 cm^-1.

112

RKR potential functions Tobias and Vanderslice, 1961, Namioka, 1965,$ 72, Spindler, 1969; see also Stwalley, 1973. Precise ab initio potential function (including diagonal corrections) and predicted vibrational levels Kolos and Wolniewicz, 1968, Kolos and Wolniewicz, 1975.

113

_v= +0.1214(v+1/2)² - 0.0117(v+1/2)³ + 0.0004₆(v+1/2)⁴, from a least squares fit Dabrowski and Herzberg, 1974 to the first eight levels. Wilkinson, 1968 gives slightly different constants based on the first five levels only. For v geq

8 there are strong rotational perturbations caused by interaction with C ¹

_u. Only after deperturbation can meaningful B_v values for these levels be obtained [see Dabrowski and Herzberg, 1974]. For a theoretical discussion of the intensities in the perturbed region see Ford, 1974.

114

D_v= -2.165E-3(v+1/2) + 2.28₉E-4(v+1/2)² - 1.18₅E-5(v+1/2)³. For individual B_v and D_v values see Herzberg and Howe, 1959, Namioka, 1964, 2, Dabrowski and Herzberg, 1974.

115

Lifetime

(v=3...7) = 0.8 ns Hesser, 1968; tau

(v=8...11) = 1.0 ns Smith and Chevalier, 1972.

116

Franck-Condon factors from RKR potentials Halmann and Laulicht, 1966, Spindler, 1969; from ab initio potential functions Dalgarno and Allison, 1968, Allison and Dalgarno, 1970, Allison and Dalgarno, 1970, 2, including theoretical oscillator strengths; see also Lin, 1975. J dependence of Franck-Condon factors and transition probabilities Villarejo, Stockbauer, et al., 1969, Wolniewicz, 1969, Becker and Fink, 1971. Experimental Franck-Condon factors and oscillator strengths Geiger and Topschowsky, 1966, Haddad, Lokan, et al., 1968, Hesser, Brooks, et al., 1968, Geiger and Schmoranzer, 1969, Fabian and Lewis, 1974, Lewis, 1974, Schmoranzer, 1975; Sigma

f_v'0 = 0.29. Variation of transition moment with r Hesser, Brooks, et al., 1968, Geiger and Schmoranzer, 1969, Schmoranzer, 1975 and, ab initio, Dalgarno and Allison, 1968, Wolniewicz, 1969. Selective enhancements of v=3 and 10 of B ¹ Sigma

_u^- in an Ar-H₂ mixture, first observed by Lyman, have recently been studied by Takezawa, Innes, et al., 1966; similar enhancements were also observed in Kr-H₂ mixtures. Stimulated emission in the P branches of the 3-10, 4-11, 5-12, 6-13, 7-13 Lyman bands Hodgson, 1970, Waynant, Shipman, et al., 1970.

117

A continuous spectrum corresponding to transitions to the continuum of X ¹ Sigma

_g^- has been observed Dalgarno, Herzberg, et al., 1970 and the intensity distribution found to be in agreement with calculations. Dalgarno and Stephens, 1970, Stephens and Dalgarno, 1972 have calculated transition probabilities and the fractions that go to the continuum for v' = 0.... 36. Allison and Dalgarno, 1969 calculated the continuous spectrum corresponding to absorption from the ground state to the continuum of B ¹ sigma

_u^-.

118

_ex_e= +0.812₉(v+1/2)³; these constants Foltz, Rank, et al., 1966 represent only the levels v=0,1,2,3. Herzberg and Howe, 1959 has less accurate constants representing higher G(v) values. "True" omega

_e= 4403.₂ Fink, Wiggins, et al., 1965 (including Dunham corrections) Fink, Wiggins, et al., 1965. The zero-point energy (Y₀₀ = 8.9₃ included) is 2179.2₇ cm^-1. Herzberg and Monfils, 1960.

119

RKR potential functions Tobias and Vanderslice, 1961, Weissman, Vanderslice, et al., 1963, Ginter and Battino, 1965, see also Zhirnov and Vasilevskii, 1970; ab initio potential functions Kolos and Wolniewicz, 1974, Kolos and Wolniewicz, 1975, 2. Rotational and vibrational levels calculated from the latter are given in Kolos and Wolniewicz, 1975, 2; see also Waech and Bernstein, 1967, Kolos and Wolniewicz, 1968, 2. Waech and Bernstein, 1967 include some of the quasi-bound levels above the dissociation limit [see also Allison, 1969]; for their experimental observation see Herzberg and Howe, 1959, Herzberg and Mckenzie, 1979. Recent comparisons between ab initio calculated and observed energy levels Bunker, 1972, Orlikowski and Wolniewicz, 1974, Dabrowski and Herzberg, 1976, Bishop and Shih, 1976.

120

_v= +0.057₇(v+1/2)² - 0.005₁(v+1/2)³; these constants Foltz, Rank, et al., 1966 represent only B_0...3 which are the best known B_v values. Brannon, Church, et al., 1968 from the field-induced spectrum give a very slightly different B₀ (59.334₃ versus 59.336₂); see also Buijs and Gush, 1971. The formula B_v= 60.863₅ - 3.0763₈(v+1/2) + 0.0601₇(v+1/2)² - 0.0048_l(v+1/2)³ (v leq

8) of Herzberg and Howe, 1959 holds up to v=8. Higher B_v values Herzberg and Howe, 1959 require higher and higher terms in the formula. All the constants given are Y₀₁,...Y₃₁ values; Fink, Wiggins, et al., 1965 have introduced Dunham corrections and give the "true" B_e = 60.867₉ Fink, Wiggins, et al., 1965. According to Ramsey, 1952 the hyperfine levels F=1 and 2 for J=1,v=0 are 1.823E-5 and 2.005E-5 cm^-1 below the F=0 component.

121

D_v= -0.0027₄(v+1/2) + 0.0004₀(v+1/2)²; H_v = [4.9-0.5(v+1/2)]E-5 Fink, Wiggins, et al., 1965; see also Foltz, Rank, et al., 1966.

122

Quadrupole 130 and field-induced sp..131

123

Raman cross sections Harney, Randolph, et al., 1975.

124

Rotational g factor g_J = 0.88291.

125

This is an upper limit (36118.3 ± 0.5 cm^-1), the lower limit being 4.4779 eV. According to Herzberg, 1970 the true value is probably close to the upper limit; see also Stwalley, 1970 who gives D₀⁰ = 36118.6 cm^-1 Stwalley, 1970 on the basis of a reassignment of the last vibrational levels of the B state. The most recent theoretical value of Kolos and Wolniewicz, 1968, 2 - including a small non-adiabatic correction of Bunker, 1979 - is D₀⁰= 36117.9 cm^-1 Kolos and Wolniewicz, 1968, 2, Bunker, 1979. An earlier independent calculation Hunter, 1966 (not including the non-adiabatic correction) gave D₀⁰= 36118.1 cm^-1 Hunter, 1966.

126

From the limit of the np sigma

, ¹

_u⁺ Rydberg series (124417.2 cm^-1) taking account of perturbations and pressure shift of high n lines Herzberg and Jungen, 1972. The earlier value of Takezawa, 1970, 2 was higher by 1.2 cm^-1 because it was not corrected for pressure shift. The latest theoretical (ab initio) value Jeziorski and Kolos, 1969 including relativistic, Lamb shift, and non-adiabatic corrections is 15.4259₀ eV; see Herzberg and Jungen, 1972.

127

The two J=2 levels are observed at 27631.3 and 27732.9 cm^-1 above J=0, v=0 of B ¹ Sigma

_u⁺ Dieke, 1958. The

₀₀ value given is an extrapolated average for J=0 and, because of the uncoupling, is rather uncertain.

128

The two J=1 levels are observed at 27385.8 and 27487.1 cm^-1 above J=0, v=0 of B ¹ Sigma

_u⁺ Dieke, 1958. The

₀₀ value given is an extrapolated average for J=0 and, because of the uncoupling, is rather uncertain.

129

Vibrational numbering of Kolos and Wolniewicz, 1969. See 98.

130

Fink, Wiggins, et al., 1965 give absolute intensity measurements of the quadrupole rotation-vibration spectrum (1-0, 2-0, 3-0) as well as corrections for pressure shifts; see also Margolis, 1973, McKellar, 1974, Chackerian and Giver, 1975. Dependence of quadrupole moment on r Kolos and Wolniewicz, 1965. Predicted intensities in the rotation-vibration spectrum James, 1969, in the rotation spectrum Dalgarno and Wright, 1972. Predicted lifetimes of rotation-vibration levels Black and Dalgarno, 1976, e.g. tau

(v=1,J=1)= 1.17E+6 s Black and Dalgarno, 1976.

131

The rotation and rotation-vibration spectrum has been observed in pressure- induced absorption, see the review by Welsh, 1972.

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Schmoranzer, 1975
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Notes

Symbols used in this document:

AE	Appearance energy
IE (evaluated)	Recommended ionization energy
P_c	Critical pressure
P_triple	Triple point pressure
S°_{gas,1 bar}	Entropy of gas at standard conditions (1 bar)
T	Temperature
T_c	Critical temperature
T_triple	Triple point temperature
d(ln(k_H))/d(1/T)	Temperature dependence parameter for Henry's Law constant
k°_H	Henry's Law constant at 298.15K
_rG°	Free energy of reaction at standard conditions
_rH°	Enthalpy of reaction at standard conditions
_rS°	Entropy of reaction at standard conditions
_c	Critical density

Data from NIST Standard Reference Database 69: NIST Chemistry WebBook
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NIST Chemistry WebBook, SRD 69

Hydrogen

Data at NIST subscription sites:

Gas phase thermochemistry data

Gas Phase Heat Capacity (Shomate Equation)

Phase change data

Antoine Equation Parameters

Reaction thermochemistry data

Reactions 1 to 50

Free energy of reaction

Enthalpy of reaction

Enthalpy of reaction

Enthalpy of reaction

Henry's Law data

Henry's Law constant (water solution)

Gas phase ion energetics data

Ionization energy determinations

Appearance energy determinations

De-protonation reactions

Ion clustering data

Clustering reactions

Free energy of reaction

Enthalpy of reaction

Enthalpy of reaction

Enthalpy of reaction

Mass spectrum (electron ionization)

Spectrum

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Additional Data

Constants of diatomic molecules

Notes

References

Notes