Methylidyne

Formula: CH
Molecular weight: 13.0186
IUPAC Standard InChI: InChI=1S/CH/h1H
IUPAC Standard InChIKey: VRLIPUYDFBXWCH-UHFFFAOYSA-N
CAS Registry Number: 3315-37-5
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:
- CD
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Gas phase thermochemistry data

Go To: Top, Gas phase ion energetics data, Constants of diatomic molecules, References, Notes

Quantity	Value	Units	Method	Reference	Comment
Δ_fH°_gas	142.00	kcal/mol	Review	Chase, 1998	Data last reviewed in December, 1967
Quantity	Value	Units	Method	Reference	Comment
S°_{gas,1 bar}	43.748	cal/mol*K	Review	Chase, 1998	Data last reviewed in December, 1967

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. to 1100.	1100. to 6000.
A	7.873351	7.206901
B	-3.993920	2.020821
C	5.780581	-0.470756
D	-1.860591	0.036871
E	-0.015583	-1.190271
F	139.7300	137.8320
G	54.13810	50.03659
H	142.0000	142.0000
Reference	Chase, 1998	Chase, 1998
Comment	Data last reviewed in December, 1967	Data last reviewed in December, 1967

Gas phase ion energetics data

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Data evaluated as indicated in comments:
L - Sharon G. Lias

Data compiled as indicated in comments:
B - John E. Bartmess
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 CH⁺ (ion structure unspecified)

Quantity	Value	Units	Method	Reference	Comment
IE (evaluated)	10.64 ± 0.01	eV	N/A	N/A	L

Electron affinity determinations

EA (eV)	Method	Reference	Comment
1.260 ± 0.020	N/A	Goebbert, 2012	B
1.2380 ± 0.0078	LPES	Kasdan, Herbst, et al., 1975	B
0.740 ± 0.050	PD	Feldman, 1970	B
2.60 ± 0.30	EIAE	Locht and Momigny, 1970	From CH₄,C₂H₂,C₂H₄; B

Ionization energy determinations

IE (eV)	Method	Reference	Comment
10.64	EVAL	Huber and Herzberg, 1979	LLK
10.64 ± 0.01	S	Herzberg and Johns, 1969	RDSH

De-protonation reactions

+ = Methylidyne

By formula: C^- + H⁺ = CH

Quantity	Value	Units	Method	Reference	Comment
Δ_rH°	365.54 ± 0.17	kcal/mol	D-EA	Scheer, Bilodeau, et al., 1998	gas phase; Given: 1.262119(20) eV; B
Quantity	Value	Units	Method	Reference	Comment
Δ_rG°	360.00 ± 0.27	kcal/mol	H-TS	Scheer, Bilodeau, et al., 1998	gas phase; Given: 1.262119(20) eV; B

Constants of diatomic molecules

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

Data collected through August, 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 ¹²C¹H
State	T_e	ω_e	ω_ex_e	ω_ey_e	B_e	α_e	γ_e	D_e	β_e	r_e	Trans.	ν₀₀
Rydberg	Several unassigned absorption bands 1 above 80000 cm^-1.
	↳Herzberg and Johns, 1969
	Rydberg series joining on to G, ν = 85850 -R/(n-0.09)²; n = 3,4,5,6
	↳missing citation
G	[74373] 2										G ← X	72960
G	↳missing citation
F ²Σ⁺	[65945]				[12.17] 3					[1.221]	F ← X R	64531.5 4 Z
F ²Σ⁺	↳missing citation
State	T_e	ω_e	ω_ex_e	ω_ey_e	B_e	α_e	γ_e	D_e	β_e	r_e	Trans.	ν₀₀
E ²Π	[65625]				[12.6] 5					[1.2]	E ← X R	64211.7 4 Z
E ²Π	↳missing citation
D ²Π_i	[60394] 6				[13.7] 5					[1.15]	D ← B V	33282.8 4 Z
	↳missing citation
											D ← X	58981 4 Z
	↳missing citation
C ²Σ⁺	31801.5	2840.2 Z	125.96 7	13.55	14.603 8 9	0.7185 10		[0.001555] 11		1.1143	C ↔ X 12 13 VR	31778.1 4 Z
C ²Σ⁺	↳Heimer, 1932; Gero, 1941; missing citation; Herzberg and Johns, 1969
State	T_e	ω_e	ω_ex_e	ω_ey_e	B_e	α_e	γ_e	D_e	β_e	r_e	Trans.	ν₀₀
B ²Σ^-	(26044)	[1794.9] 14 Z			[12.645] 15 9	16		[0.00222] 17		[1.1975]	B ↔ X 18 13 R	25698.2 4 Z
B ²Σ^-	↳missing citation; Gero, 1941; missing citation; missing citation
A ²Δ	23189.8 19	2930.7 Z	96.65		14.934 20 9	0.697		0.00154	0.00004	1.1019	A ↔ X 21 13 V	23217.5 4 Z
A ²Δ	↳Gero, 1941; Kiess and Broida, 1956; missing citation; missing citation
a ⁴Σ^-	(5844)	(3145)	(72)		(15.4)	(0.55)				(1.085)		5985 22
a ⁴Σ^-	↳Kasdan, Herbst, et al., 1975
X ²Π_r	0 23	2858.5 Z	63.02		14.457 24 25 9	0.534		0.00145		1.1199 26
	↳Rydbeck, Ellder, et al., 1973
	Ab initio calculations
	↳Meyer and Rosmus, 1975

Notes

According to theoretical work Walker and Kelly, 1972 they represent the nf series.

3d complex consisting of ²Σ, ²Π, ²Δ.

Spin splitting constant γ₀= +0.62. Heterogeneous predissociation.

The band origins refer to the zero points of the Hill-Van Vleck formulae for the ground and excited (Λ ≠ 0) states. See also Garstang, 1963.

Homogeneous predissociation.

A= -28.5.

ω_ez_e = -3.957; from CD using isotope relations.

Spin splitting constant γ ~ +0.05 Herzberg and Johns, 1969, Botterud, Lofthus, et al., 1973. Predissociation, see 12.

Slightly different sets of constants from the same data are given by Botterud, Lofthus, et al., 1973 for X, A, B, C and Krupp, 1974 for X, A. Precise values for the rotational energy levels of X ²Π(v=0) in Douglas and Elliott, 1965; tables of term values for levels of X, A, B,C in Botterud, Lofthus, et al., 1973.

α_v= +0.0258(v+1/2)² - 0.023(v+1/2)³; see 7 .

D₁ = 16.7E-4, D₂ = 20E-4.

Lifetime of C ²Σ⁺ anomalously small on account of predissociation Hesser and Lutz, 1968, Herzberg and Johns, 1969, Hesser and Lutz, 1970, Elander and Smith, 1973. According to Brzozowski, Bunker, et al., 1976 the lifetime in v=0 varies from 10 ns at N=1 to 25 ns at N=24 and is even shorter in v=1. The previous observation of different lifetimes for F₁ and F₂ levels is not confirmed. The lifetime for CD is more than twice that for CH Hesser and Lutz, 1970 indicating that predissociation is weaker Herzberg and Johns, 1969. Ab initio theory Hinze, Lie, et al., 1975 gives a radiative lifetime τ(v=0) = 89 ns Hinze, Lie, et al., 1975 suggesting that the radiationless and the radiative transition probabilities are approximately in the ratio 8 to 1 Brzozowski, Bunker, et al., 1976. From absorption experiments Linevsky, 1967 an f value of f= 0.006 Linevsky, 1967 was derived for the C-X transition.

Wavenumber and wavelength tables and comparisons with the solar spectrum published by Moore and Broida, 1959. ¹³CH lines for A-X measured by Richter and Tonner, 1967 and used to determine ¹³C/¹²C ratio in the sun. Franck-Condon factors Halmann and Laulicht, 1966, Liszt and Smith, 1972. The laboratory absorption spectrum was first observed by Norrish, Porter, et al., 1953 in the acetylene combustion initiated by the flash photolysis of NO₂; in flames by Gaydon, Spokes, et al., 1960; and more recently by Bleekrode and Nieuwpoort, 1965, Bleekrode, 1966, Herzberg and Johns, 1969.

Very shallow potential curve; ω_e ~ 2251, ω_ex_e ~ 230 (from CD). A small potential maximum has been established in this state Herzberg and Johns, 1969; confirmed by theoretical calculations Lie, Hinze, et al., 1972.

Spin splitting constant γ₀= -0.0285 Gero, 1941, γ₁ = -0.020 Herzberg and Johns, 1969. Breaking off in emission above v'=0, N'=15 and v'=1, N'=6 and broadening in absorption at higher N' due to predissociation; see also 18. Selective excitation of v'=1 in hydrogen flames and suppression of breaking off Durie, 1952.

B₁= 11.160.

D₁= 32.8E-4.

Radiative lifetime τ= 0.38 μs Fink and Welge, 1967, Linevsky, 1967, Hesser and Lutz, 1970 corresponding to f~0.0029 Fink and Welge, 1967, Linevsky, 1967, Hesser and Lutz, 1970. Brooks and Smith, 1974 and Brzozowski, Bunker, et al., 1976 have measured lifetimes of individual rotational lines finding a regular increase from 0.32 to 0.38 μs from N'=2 to 14 (v'=0); sudden drop to 0.12 μs for N'=15 due to predissociation: see, however, Anderson, Peacher, et al., 1975. In v'= 1 the lifetime is 0.40 μs until breaking off occurs between N'= 6 and 7.

A= -1.0₂ Herzberg and Johns, 1969, see also Kiess and Broida, 1956, Botterud, Lofthus, et al., 1973.

Stark effect, μ_el(v=0) = 0.89 D Scarl and Dalby, 1974.

Lifetime τ(v=0) = 0.53₄ μs Brzozowski, Bunker, et al., 1976 corresponding to f=0.0053 Brzozowski, Bunker, et al., 1976: superseding earlier less precise values by Bennett and Dalby, 1960, Fink and Welge, 1967, Hesser and Lutz, 1970, Smith, 1971, Jorgensen and Sorensen, 1975. Kuz'menko, Kuzyakov, et al., 1972 from shock tube absorption measurements obtain f_e = 0.0019 Kuz'menko, Kuzyakov, et al., 1972. A theoretical f₀₀ = 0.0068 Hinze, Lie, et al., 1975 is given in Hinze, Lie, et al., 1975. The observation of a reduced lifetime in v=1 for N>11 Brzozowski, Bunker, et al., 1976 suggests a weak predissociation probably caused by X ²Π.

T₀, from laser photoelectron spectrometry of CH- Kasdan, Herbst, et al., 1975. Theoretical calculations Lie, Hinze, et al., 1972 give 5395 cm^-1. The vibrational and rotational constants given are theoretical values; see also Liu and Verhaegen, 1970.

A = +27.95. Slightly higher values in Goss, 1966 and Botterud, Lofthus, et al., 1973.

Λ-type doubling, Δv ~ 0.038N(N+1) - .... For the lowest J values more complicated formulae apply, see Douglas and Elliott, 1965 and Goss, 1966. The transition between the two Λ components of J=1/2 has been observed with its hyperfine structure in emission in interstellar clouds Rydbeck, Ellder, et al., 1973. The derived J=1/2 Λ-doublet separation is 3320.987 MHz, close to earlier predictions by Douglas and Elliott, 1965, Baird and Bredohl, 1971 and a subsequent theoretical calculation by Hammersley and Richards, 1974. Predicted Λ- doubling and hyperfine splittings for other J values in Levy and Hinze, 1975.

Stark effect, μ_el = 1.46 D Phelps and Dalby, 1966.

Λ doubling sp. 24

From the predissociation in the B state Herzberg and Johns, 1969 as modified by Brooks and Smith, 1974 and Brzozowski, Bunker, et al., 1976. Confirmed thermochemically by Brewer and Kester, 1964.

From Rydberg series Herzberg and Johns, 1969. Theoretical photoionization cross section Walker and Kelly, 1972, 2.

References

Go To: Top, Gas phase thermochemistry data, Gas phase ion energetics data, Constants of diatomic molecules, Notes

Chase, 1998
Chase, M.W., Jr., NIST-JANAF Themochemical Tables, Fourth Edition, J. Phys. Chem. Ref. Data, Monograph 9, 1998, 1-1951. [all data]

Goebbert, 2012
Goebbert, D.J., Photoelectron imaging of CH-, Chem. Phys. Lett., 2012, 551, 19-25, https://doi.org/10.1016/j.cplett.2012.08.065 . [all data]

Kasdan, Herbst, et al., 1975
Kasdan, A.; Herbst, E.; Lineberger, W.C., Laser photoelectron spectrometry of CH₂^-, Chem. Phys. Lett., 1975, 31, 78. [all data]

Feldman, 1970
Feldman, D., Photoablosung von Elektronen bei einigen Stabilen Negativen Ionen, Z. Naturfor., 1970, 25A, 621. [all data]

Locht and Momigny, 1970
Locht, R.; Momigny, J., Mass Spectrometric Determination of the Electron Affinities of Radicals, Chem. Phys. Lett., 1970, 6, 4, 273, https://doi.org/10.1016/0009-2614(70)85072-2 . [all data]

Huber and Herzberg, 1979
Huber, K.P.; Herzberg, G., Molecular Spectra and Molecular Structure. IV. Constants of Diatomic Molecules,, Van Nostrand Reinhold Co., 1979, ,1. [all data]

Herzberg and Johns, 1969
Herzberg, G.; Johns, J.W.C., New spectra of the CH molecule, Astrophys. J., 1969, 158, 399. [all data]

Scheer, Bilodeau, et al., 1998
Scheer, M.; Bilodeau, R.C.; Brodie, C.A.; Haugen, H.K., Systematic study of the stable states of C-, Si-, Ge-, and Sn- via infrared laser spectroscopy, Phys. Rev. A, 1998, 58, 4, 2844-2856, https://doi.org/10.1103/PhysRevA.58.2844 . [all data]

Heimer, 1932
Heimer, T., Untersuchung uber die kohlenwasserstoffbande λ3143, Z. Phys., 1932, 78, 771. [all data]

Gero, 1941
Gero, L., Vervollstandigung der analyse der CH-Banden, Z. Phys., 1941, 118, 27. [all data]

Kiess and Broida, 1956
Kiess, N.H.; Broida, H.P., Analysis of the (0, 1) and (1, 2) bands of the ²Δ-²Π system of CH, Astrophys. J., 1956, 123, 166. [all data]

Rydbeck, Ellder, et al., 1973
Rydbeck, O.E.H.; Ellder, J.; Irvine, W.M., Radio detection of interstellar CH, Nature (London), 1973, 246, 466. [all data]

Meyer and Rosmus, 1975
Meyer, W.; Rosmus, P., PNO-Cl and CEPA studies of electron correlation effects. III. Spectroscopic constants and dipole moment functions for the ground states of the first-row and second-row diatomic hydrides, J. Chem. Phys., 1975, 63, 2356. [all data]

Walker and Kelly, 1972
Walker, T.E.H.; Kelly, H.P., Rydberg states of CH, J. Chem. Phys., 1972, 57, 936. [all data]

Garstang, 1963
Garstang, R.H., Revised molecular constants for the CH and CD spectra, Proc. Phys. Soc. London, 1963, 82, 545. [all data]

Botterud, Lofthus, et al., 1973
Botterud, I.; Lofthus, A.; Veseth, L., Term values and molecular parameters for CH and CH⁺, Phys. Scr., 1973, 8, 218. [all data]

Krupp, 1974
Krupp, B.M., A new analysis of the A²Δ-X²Π system of CH, Astrophys. J., 1974, 189, 389. [all data]

Douglas and Elliott, 1965
Douglas, A.E.; Elliott, G.A., Laboratory investigations of the interstellar radio-frequency lines of CH and other molecules, Can. J. Phys., 1965, 43, 496. [all data]

Hesser and Lutz, 1968
Hesser, J.E.; Lutz, B.L., Direct measurements of predissociation probabilities in CH and CD molecules, Phys. Rev. Lett., 1968, 20, 363. [all data]

Hesser and Lutz, 1970
Hesser, J.E.; Lutz, B.L., Probabilities for radiation and predissociation. II. The excited states of CH, CD, and CH⁺, and some astrophysical implications, Astrophys. J., 1970, 159, 703. [all data]

Elander and Smith, 1973
Elander, N.; Smith, W.H., Predissociation in the C²Σ⁺ state of CH and its astrophysical implications, Astrophys. J., 1973, 184, 663-670. [all data]

Brzozowski, Bunker, et al., 1976
Brzozowski, J.; Bunker, P.; Elander, N.; Erman, P., Predissocation effects in the A, B, and C states of CH and the interstellar formation rate of CH via inverse predissociation, Astrophys. J., 1976, 207, 414. [all data]

Hinze, Lie, et al., 1975
Hinze, J.; Lie, G.C.; Liu, B., Valence excited states of CH. III. Radiative lifetimes, Astrophys. J., 1975, 196, 621. [all data]

Linevsky, 1967
Linevsky, M.J., Relative oscillator strengths of CH. The heat of dissocaition of CH, J. Chem. Phys., 1967, 47, 3485. [all data]

Moore and Broida, 1959
Moore, C.E.; Broida, H.P., CH in the solar spectrum, J. Res. Nat. Bur. Stand. Sect. A, 1959, 63, 19. [all data]

Richter and Tonner, 1967
Richter, J.; Tonner, K.-F., Bestimmung des Haufigkeitsverhaltnisses C¹²/C¹³ in der Sonnenatmosphare, Z. Astrophys., 1967, 67, 155. [all data]

Halmann and Laulicht, 1966
Halmann, M.; Laulicht, I., Isotope effects on vibrational transition probabilities. IV. Electronic transitions of isotopic C₂, CO, CN, H₂, and CH molecules, Astrophys. J. Suppl. Ser., 1966, 12, 307. [all data]

Liszt and Smith, 1972
Liszt, H.S.; Smith, W.H., RKR Franck-Condon factors for blue and ultraviolet transitions of some molecules of astrophysical interest and some comments on the interstellar abundance of CH, CH⁺, and SiH, J. Quant. Spectrosc. Radiat. Transfer, 1972, 12, 947. [all data]

Norrish, Porter, et al., 1953
Norrish, R.G.W.; Porter, G.; Thrush, B.A., Studies of the explosive combustion of hydrocarbons by kinetic spectroscopy. I. Free radical absorption spectra in acetylene combustion, Proc. R. Soc. London A, 1953, 216, 165. [all data]

Gaydon, Spokes, et al., 1960
Gaydon, A.G.; Spokes, G.N.; Suchtelen, J.V., Absorption spectra of low-pressure flames, Proc. R. Soc. London A, 1960, 256, 323. [all data]

Bleekrode and Nieuwpoort, 1965
Bleekrode, R.; Nieuwpoort, W.C., Absorption and emission measurements of C₂ and CH electronic bands in low-pressure oxyacetylene flames, J. Chem. Phys., 1965, 43, 3680. [all data]

Bleekrode, 1966
Bleekrode, Thesis, Amsterdam, 1966, 0. [all data]

Lie, Hinze, et al., 1972
Lie, G.C.; Hinze, J.; Liu, B., Calculated a ⁴Σ^-, A²Δ, B²Σ^- states of CH, J. Chem. Phys., 1972, 57, 625. [all data]

Durie, 1952
Durie, R.A., The excitation and intensity distribution of CH bands in flames, Proc. Phys. Soc. London Sect. A, 1952, 65, 125. [all data]

Fink and Welge, 1967
Fink, E.H.; Welge, K.H., Lifetime measurements on CH(A²Δ), CH(B²Σ^-), and C₂(A³Π_g) by the phase-shift method, J. Chem. Phys., 1967, 46, 4315. [all data]

Brooks and Smith, 1974
Brooks, N.H.; Smith, W.H., Radiative and predissociation probabilities for individual rotational levels of the B²Σ^- state of CH with application to the radiative recombination of CH in the interstellar medium, Astrophys. J., 1974, 194, 513. [all data]

Anderson, Peacher, et al., 1975
Anderson, R.A.; Peacher, J.; Wilcox, D.M., Radiative lifetime of the B²Σ^- state of CH, J. Chem. Phys., 1975, 63, 5287. [all data]

Scarl and Dalby, 1974
Scarl, E.A.; Dalby, F.W., High field Stark effects in CH and NH, Can. J. Phys., 1974, 52, 1429. [all data]

Bennett and Dalby, 1960
Bennett, R.G.; Dalby, F.W., Experimental oscillator strength of CH and NH, J. Chem. Phys., 1960, 32, 1716. [all data]

Smith, 1971
Smith, W.H., Absolute oscillator strengths for the CH⁺, CD⁺, and BH A¹Π-X¹Σ⁺ transition, J. Chem. Phys., 1971, 54, 1384. [all data]

Jorgensen and Sorensen, 1975
Jorgensen, S.W.; Sorensen, G., Radiative lifetimes in molecules studied by means of fast, molecular ion beams, J. Chem. Phys., 1975, 62, 2550. [all data]

Kuz'menko, Kuzyakov, et al., 1972
Kuz'menko, N.E.; Kuzyakov, Yu.Ya.; Kuznetsova, L.A.; Kudryumova, I.N.; Chuev, B.N., Experimental determination of the oscillator strength in the A²Δ-X²Π electron transition for the carbon monohydride (CH) molecule, High Temp. Engl. Transl., 1972, 9, 823, In original 905. [all data]

Liu and Verhaegen, 1970
Liu, H.P.D.; Verhaegen, G., Electronic states of CH and NH⁺, J. Chem. Phys., 1970, 53, 735. [all data]

Goss, 1966
Goss, W.M., A new determination of the frequency of the interstellar radio line of CH, Astrophys. J., 1966, 145, 3, 707-714. [all data]

Baird and Bredohl, 1971
Baird, K.M.; Bredohl, H., A laboratory determination of the frequency of the 10-centimeter radio line of CH by optical measurements, Astrophys. J., 1971, 169, 83. [all data]

Hammersley and Richards, 1974
Hammersley, R.E.; Richards, W.G., Λ-type doubling in the CH molecule, Nature (London), 1974, 251, 597-598. [all data]

Levy and Hinze, 1975
Levy, D.H.; Hinze, J., Hyperfine and Λ-doubling splitting in excited rotational levels of CH, Astrophys. J., 1975, 200, 236. [all data]

Phelps and Dalby, 1966
Phelps, D.H.; Dalby, F.W., Experimental determination of the electric dipole moment of the ground electronic state of CH, Phys. Rev. Lett., 1966, 16, 3. [all data]

Brewer and Kester, 1964
Brewer, R.G.; Kester, F.L., Dissociation energy of the CH radical, J. Chem. Phys., 1964, 40, 812. [all data]

Walker and Kelly, 1972, 2
Walker, T.E.H.; Kelly, H.P., The photoionization cross section for diatomic CH, Chem. Phys. Lett., 1972, 16, 511. [all data]

Notes

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Symbols used in this document:

EA	Electron affinity
IE (evaluated)	Recommended ionization energy
S°_{gas,1 bar}	Entropy of gas at standard conditions (1 bar)
Δ_fH°_gas	Enthalpy of formation of gas at standard conditions
Δ_rG°	Free energy of reaction at standard conditions
Δ_rH°	Enthalpy of reaction at standard conditions

Data from NIST Standard Reference Database 69: NIST Chemistry WebBook
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