Dipotassium

Formula: K₂
Molecular weight: 78.1966
IUPAC Standard InChI: InChI=1S/2K
IUPAC Standard InChIKey: ZDHURYWHEBEGHO-UHFFFAOYSA-N
CAS Registry Number: 25681-80-5
Chemical structure:
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Other data available:
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Gas phase thermochemistry data

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Quantity	Value	Units	Method	Reference	Comment
Δ_fH°_gas	123.68	kJ/mol	Review	Chase, 1998	Data last reviewed in December, 1983
Quantity	Value	Units	Method	Reference	Comment
S°_{gas,1 bar}	249.71	J/mol*K	Review	Chase, 1998	Data last reviewed in December, 1983

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 (J/mol*K)
H° = standard enthalpy (kJ/mol)
S° = standard entropy (J/mol*K)
t = temperature (K) / 1000.

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View table.

Temperature (K)	298. - 1300.	1300. - 6000.
A	22.65879	31.01331
B	53.55520	-5.786221
C	-56.32668	1.157994
D	16.00840	-0.078852
E	0.349515	12.42895
F	116.1901	134.1629
G	265.4874	307.2290
H	123.6832	123.6832
Reference	Chase, 1998	Chase, 1998
Comment	Data last reviewed in December, 1983	Data last reviewed in December, 1983

Reaction thermochemistry 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. A general reaction search form is also available. Future versions of this site may rely on reaction search pages in place of the enumerated reaction displays seen below.

Individual Reactions

K₈⁺ + Dipotassium = (K₈⁺ • )

By formula: K₈⁺ + K₂ = (K₈⁺ • K₂)

Quantity	Value	Units	Method	Reference	Comment
Δ_rH°	84.9	kJ/mol	PDiss	Brechignac, Cahuzac, et al., 1990	gas phase

K₉⁺ + Dipotassium = (K₉⁺ • )

By formula: K₉⁺ + K₂ = (K₉⁺ • K₂)

Quantity	Value	Units	Method	Reference	Comment
Δ_rH°	53.1	kJ/mol	PDiss	Brechignac, Cahuzac, et al., 1990	gas phase

K₁₁⁺ + Dipotassium = (K₁₁⁺ • )

By formula: K₁₁⁺ + K₂ = (K₁₁⁺ • K₂)

Quantity	Value	Units	Method	Reference	Comment
Δ_rH°	65.7	kJ/mol	PDiss	Brechignac, Cahuzac, et al., 1990	gas phase

K₁₃⁺ + Dipotassium = (K₁₃⁺ • )

By formula: K₁₃⁺ + K₂ = (K₁₃⁺ • K₂)

Quantity	Value	Units	Method	Reference	Comment
Δ_rH°	68.6	kJ/mol	PDiss	Brechignac, Cahuzac, et al., 1990	gas phase

K₃⁺ + Dipotassium = (K₃⁺ • )

By formula: K₃⁺ + K₂ = (K₃⁺ • K₂)

Quantity	Value	Units	Method	Reference	Comment
Δ_rH°	66.5	kJ/mol	PDiss	Brechignac, Cahuzac, et al., 1990	gas phase

K₄⁺ + Dipotassium = (K₄⁺ • )

By formula: K₄⁺ + K₂ = (K₄⁺ • K₂)

Quantity	Value	Units	Method	Reference	Comment
Δ_rH°	57.7	kJ/mol	PDiss	Brechignac, Cahuzac, et al., 1990	gas phase

K₆⁺ + Dipotassium = (K₆⁺ • )

By formula: K₆⁺ + K₂ = (K₆⁺ • K₂)

Quantity	Value	Units	Method	Reference	Comment
Δ_rH°	79.9	kJ/mol	PDiss	Brechignac, Cahuzac, et al., 1990	gas phase

K₅⁺ + Dipotassium = (K₅⁺ • )

By formula: K₅⁺ + K₂ = (K₅⁺ • K₂)

Quantity	Value	Units	Method	Reference	Comment
Δ_rH°	76.1	kJ/mol	PDiss	Brechignac, Cahuzac, et al., 1990	gas phase

K₇⁺ + Dipotassium = (K₇⁺ • )

By formula: K₇⁺ + K₂ = (K₇⁺ • K₂)

Quantity	Value	Units	Method	Reference	Comment
Δ_rH°	90.8	kJ/mol	PDiss	Brechignac, Cahuzac, et al., 1990	gas phase

K₁₀⁺ + Dipotassium = (K₁₀⁺ • )

By formula: K₁₀⁺ + K₂ = (K₁₀⁺ • K₂)

Quantity	Value	Units	Method	Reference	Comment
Δ_rH°	59.0	kJ/mol	PDiss	Brechignac, Cahuzac, et al., 1990	gas phase

K₁₂⁺ + Dipotassium = (K₁₂⁺ • )

By formula: K₁₂⁺ + K₂ = (K₁₂⁺ • K₂)

Quantity	Value	Units	Method	Reference	Comment
Δ_rH°	68.6	kJ/mol	PDiss	Brechignac, Cahuzac, et al., 1990	gas phase

Constants of diatomic molecules

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

Data collected through January, 1977

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 ³⁹K₂
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
Unidentified diffuse emission bands, 17460 - 17840 cm^-1.
↳Rebbeck and Vaughan, 1971
Diffuse bands close to lines of the principal series of K; fragments of additional systems.
↳Kuhn, 1932; Chakraborti, 1937; Okuda, 1936
G	28091	64.9₀ 1 H	0.55								G ← X R	28077 H
G	↳Yoshinaga, 1937
F	27571	62.2₉ 1 H	0.2₄								F ← X R	27556 H
F	↳Yoshinaga, 1937
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	26494.₀	61.₈ 2 H	0.2₈								E ← X R	26478.₉ H
E	↳Yoshinaga, 1937; Sinha, 1950
D	24627.7	61.60 H	0.90 3	0.0010							D ← X R	24612.3 H
D	↳Sinha, 1948
C ¹Π_u	22969.4₃	61.48₅ Z	0.13₃		0.04404	0.00011	3E-6			4.433	C ← X R	22954.2₀ Z
C ¹Π_u	↳Yamamoto, 1929; Sinha, 1948; Robertson and Barrow, 1961
B ¹Π_u	15376.7₄	75.00	0.3876 4	4.366E-3	0.04876₃ 5	0.00024		8.25E-₈		4.212₅	B 6 ↔ X 7 R	15368.2₀ Z
B ¹Π_u	↳Loomis, 1931; Loomis and Nusbaum, 1932; Tango, Link, et al., 1968
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
A ¹Σ_u⁺	11681.9	69.09 H	0.153		8						A ↔ X R	11670.5 H
A ¹Σ_u⁺	↳Crane and Christy, 1930; Sorokin and Lankard, 1971
a ³Σ_u⁺	Not observed; scattering calculations predict a very shallow potential minimum at ~8.7 Å.
a ³Σ_u⁺	↳Geittner, 1975
X ¹Σ_g⁺	0	92.021 Z	0.2829 9	-2.055E-3	0.056743	0.000165 10		8.63E-8		3.9051 11
X ¹Σ_g⁺	↳Kusch, Millman, et al., 1939; Logan, Cote, et al., 1952; Brooks, Anderson, et al., 1963

Notes

Analysis by Yoshinaga, 1937; not confirmed by Sinha, 1950.

Average of the constants obtained by Yoshinaga, 1937, Sinha, 1950.

ω_ez_e = -0.00030; convergence at 25590.

ω_ez_e = -0.0001830; vibrational constants for v'≤ 25 from low-resolution magnetic rotation spectra. Higher vibrational levels converge rapidly at 17160 cm^-1 above X ¹Σ_g⁺, v=0. T_e is from the analysis of high-resolution laser-induced fluorescence spectra Tango, Link, et al., 1968.

Recalculated by Tango, Link, et al., 1968, from the data of Loomis, 1931.

Radiative lifetime τ(v = 6,7,8) = 12.4 ns Tango and Zare, 1970; Baumgartner, Demtroder, et al., 1970 measured 9.7 ns.

Absorption cross sections Lapp and Harris, 1966.

A complex magnetic rotation spectrum has been observed which may be due to perturbations of A ¹Σ_u⁺ by an unidentified ³Π state Carroll, 1937.

Vibrational and rotational constants from the laser-induced B ≥ X fluorescence spectrum Tango, Link, et al., 1968.

α_v= -7.2E-6(v+1/2)² + 1.5E-7(v+1/2)³. See 9.

Mol. beam magn. reson. 14

From the convergence limit of B ¹Π_u. Thermochemical value [ Lewis, 1931, recalculated Loomis and Nusbaum, 1932] 0.56 eV.

Photoionization of K₂ Foster, Leckenby, et al., 1969; in agreement with limits (3.57 ≤ I.P. ≤ 4.11 eV) obtained from chemi-ionization thresholds Lee and Mahan, 1965, Williams, 1967, Robertson and Barrow, 1961 estimate 4.09 eV.

g_J = 0.02163 μ_N Brooks, Anderson, et al., 1963. For NMR spectrum and potassium eqQ see Kusch, Millman, et al., 1939, Logan, Cote, et al., 1952.

From D₀⁰(K₂) + I.P.(K) - I.P.(K₂). The experimentally observed limits (photoionization of potassium vapor, are 0.74 eV ≤ D₀⁰ ≤ 1.27 eV Williams, 1967. Theoretical calculations Bellomonte, Cavaliere, et al., 1974 give l eV.

Theoretical calculations Bellomonte, Cavaliere, et al., 1974.

References

Go To: Top, Gas phase thermochemistry data, Reaction thermochemistry 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]

Brechignac, Cahuzac, et al., 1990
Brechignac, C.; Cahuzac, P.; Carlier, F.; De Frutos, M.; Leyniger, J., Cohesive Energies of (K)n+ 5<n<200 from Photoevaporation Experiments, J. Chem. Phys., 1990, 93, 10, 7449, https://doi.org/10.1063/1.459418 . [all data]

Rebbeck and Vaughan, 1971
Rebbeck, M.M.; Vaughan, J.M., Unidentified diffuse bands in the spectrum of potassium, J. Phys. B:, 1971, 4, 258. [all data]

Kuhn, 1932
Kuhn, H., Uber spektren von unecht gebundenen molekulen (polarisationsmolekulen) K₂, Na₂, Cs₂ und verbreiterung von absorptionslinien, Z. Phys., 1932, 76, 782. [all data]

Chakraborti, 1937
Chakraborti, B.K., On a new type of absorption bands of potassium vapour, Indian J. Phys., 1937, 10, 155. [all data]

Okuda, 1936
Okuda, T., Narrow continuous band of potassium in the extreme red, Nature (London), 1936, 138, 168. [all data]

Yoshinaga, 1937
Yoshinaga, H., New ultraviolet absorption bands of sodium and potassium molecules, Proc. Phys. Math. Soc. Jpn., 1937, 19, 847. [all data]

Sinha, 1950
Sinha, S.P., Ultra-violet bands of K₂, Proc. Phys. Soc. London Sect. A, 1950, 63, 952. [all data]

Sinha, 1948
Sinha, S.P., Blue and ultra-violet bands of K₂, Proc. Phys. Soc. London, 1948, 60, 436. [all data]

Yamamoto, 1929
Yamamoto, Revised by Crane and Christy, 1930, 1929, 355. [all data]

Robertson and Barrow, 1961
Robertson, E.W.; Barrow, R.F., Rotational analysis oi the C¹π_u-X1⁺_g system of K₂, and the ionisation potential of K₂, Proc. Chem. Soc., 1961, 329. [all data]

Loomis, 1931
Loomis, F.W., Rotational structure of the red bands of potassium, Phys. Rev., 1931, 38, 2153. [all data]

Loomis and Nusbaum, 1932
Loomis, F.W.; Nusbaum, R.E., Magnetic rotation spectrum and heat of dissociation of the potassium molecule, Phys. Rev., 1932, 39, 89. [all data]

Tango, Link, et al., 1968
Tango, W.J.; Link, J.K.; Zare, R.N., Spectroscopy of K₂ using laser-induced fluorescence, J. Chem. Phys., 1968, 49, 4264. [all data]

Crane and Christy, 1930
Crane, W.O.; Christy, A., Vibrational quantum analysis of the potassium infrared absorption bands, Phys. Rev., 1930, 36, 421. [all data]

Sorokin and Lankard, 1971
Sorokin, P.P.; Lankard, J.R., Emission spectra of alkali-metal molecules observed with a heat-pipe discharge tube, J. Chem. Phys., 1971, 55, 3810. [all data]

Geittner, 1975
Geittner, P., Bestimmung der Triplett-Potentialdaten fur das K₂-Stossmolekul, Z. Phys., 1975, 272, 359. [all data]

Kusch, Millman, et al., 1939
Kusch, P.; Millman, S.; Rabi, I.I., The nuclear magnetic moments of N¹⁴, Na²³, K³⁹ and Cs¹³³, Phys. Rev., 1939, 55, 1176. [all data]

Logan, Cote, et al., 1952
Logan, R.A.; Cote, R.E.; Kusch, P., The sign of the quadrupole interaction energy in diatomic molecules, Phys. Rev., 1952, 86, 280. [all data]

Brooks, Anderson, et al., 1963
Brooks, R.A.; Anderson, C.H.; Ramsey, N.F., Rotational magnetic moments of diatomic alkalis, Phys. Rev. Lett., 1963, 10, 441. [all data]

Tango and Zare, 1970
Tango, W.J.; Zare, R.N., Radiative lifetime of the B¹Π_u state of K₂, J. Chem. Phys., 1970, 53, 3094. [all data]

Baumgartner, Demtroder, et al., 1970
Baumgartner, G.; Demtroder, W.; Stock, M., Lifetime-measurements of alkali-molecules excited by different laserlines, Z. Phys., 1970, 232, 462. [all data]

Lapp and Harris, 1966
Lapp, M.; Harris, L.P., Absorption cross sections of alkali-vapor molecules: I. Cs₂ in the visible. II. K₂ in the red, J. Quant. Spectrosc. Radiat. Transfer, 1966, 6, 169. [all data]

Carroll, 1937
Carroll, T., Magnetic rotation spectra of diatomic molecules, Phys. Rev., 1937, 52, 822. [all data]

Lewis, 1931
Lewis, L.C., Die bestimmung des gleichgewichts zwischen den atomen und den molekulen eines alkalidampfes mit einer molekularstrahlmethode, Z. Phys., 1931, 69, 786. [all data]

Foster, Leckenby, et al., 1969
Foster, P.J.; Leckenby, R.E.; Robbins, E.J., The ionization potentials of clustered alkali metal atoms, J. Phys. B:, 1969, 2, 478. [all data]

Lee and Mahan, 1965
Lee, Y.-T.; Mahan, B.H., Photosensitized ionization of alkali-metal vapors, J. Chem. Phys., 1965, 42, 2893. [all data]

Williams, 1967
Williams, R.A., Photoionization of potassium vapor, J. Chem. Phys., 1967, 47, 4281. [all data]

Bellomonte, Cavaliere, et al., 1974
Bellomonte, L.; Cavaliere, P.; Ferrante, G., Alkali molecular ion energies and expectation values in a model-potential treatment, J. Chem. Phys., 1974, 61, 3225. [all data]

Notes

Go To: Top, Gas phase thermochemistry data, Reaction thermochemistry data, Constants of diatomic molecules, References

Symbols used in this document:

S°_{gas,1 bar} Entropy of gas at standard conditions (1 bar)

Δ_fH°_gas Enthalpy of formation of gas 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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S°_{gas,1 bar}	Entropy of gas at standard conditions (1 bar)
Δ_fH°_gas	Enthalpy of formation of gas at standard conditions
Δ_rH°	Enthalpy of reaction at standard conditions