Dirubidium

Formula: Rb₂
Molecular weight: 170.9356
IUPAC Standard InChI: InChI=1S/2Rb
IUPAC Standard InChIKey: MQZGYYYBCTXEME-UHFFFAOYSA-N
CAS Registry Number: 25681-81-6
Chemical structure:
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Other data available:
- Gas phase ion energetics data
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Gas phase thermochemistry data

Go To: Top, Constants of diatomic molecules, References, Notes

Quantity	Value	Units	Method	Reference	Comment
Δ_fH°_gas	27.077	kcal/mol	Review	Chase, 1998	Data last reviewed in December, 1983
Quantity	Value	Units	Method	Reference	Comment
S°_{gas,1 bar}	64.783	cal/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 (cal/mol*K)
H° = standard enthalpy (kcal/mol)
S° = standard entropy (cal/mol*K)
t = temperature (K) / 1000.

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Temperature (K)	298. to 1600.	1600. to 6000.
A	7.411979	5.583311
B	7.920651	-0.346557
C	-10.32890	0.067709
D	3.161021	-0.004487
E	0.014579	3.545302
F	24.64761	31.35650
G	71.90301	77.69520
H	27.07701	27.07701
Reference	Chase, 1998	Chase, 1998
Comment	Data last reviewed in December, 1983	Data last reviewed in December, 1983

Constants of diatomic molecules

Go To: Top, Gas phase thermochemistry data, References, Notes

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

Data collected through July, 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 ⁽⁸⁵⁾Rb₂
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 features in the absorption spectrum of rubidium vapour at 37270 and 40590 cm^-1.
↳Creek and Marr, 1968
Diffuse absorption bands corresponding to van der Waals molecules.
↳Ny-Tsi-Ze and Shang-Yi, 1938
D	22777.5	40.42 H	0.0745	-0.00144							D ← X 1 R	22769.1 H
D	↳Tsi-Ze and San-Tsiang, 1937
C ¹Π_u	20835.1	36.46 H	0.124 2								C ↔ X 1 3 R	20824.7 H
C ¹Π_u	↳Tsi-Ze and San-Tsiang, 1937
"Quasicontinuous" emission 16400 - 18500 cm^-1.
↳Brom and Broida, 1974
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 ¹Π_u	14662.6	48.05 H	0.191								B ↔ X 4 R	14657.9 H
B ¹Π_u	↳Kusch, 1936
A (¹Σ_u⁺) 5											A ↔ X
A (¹Σ_u⁺) 5	↳Sorokin and Lankard, 1971; Kostin and Khodovoi, 1973; Drummond and Schlie, 1976
X ¹Σ_g⁺	0	57.31 H	0.105
X ¹Σ_g⁺	Mol. beam magn. reson. 6

Notes

Lifetime measurements by Baumgartner, Demtroder, et al., 1970 vary from 61 ns to l4 ns, the former attributed to the D state, the latter to C ¹Π_u. The two states have also been observed in two-photon ionization of Rb₂ Granneman, Klewer, et al., 1976.

Predissociation 9

Polarization studies of the fluorescence spectrum Feldman and Zare, 1976, Tam and Happer, 1976 confirm its composition of P and R as well as Q lines, contrary to the conclusions of Brom and Broida, 1974 that it consists of Q line progressions only.

Magnetic rotation spectrum Kusch, 1936. The B → X (and A → X) emission observed by Brom and Broida, 1974 is attributed to atomic recombination of Rb(5²P) and Rb(5²S), the former formed in the predissociation of Rb₂ C ¹Π_u.

Unresolved band system 9200 - 12500 cm^-1. 10

g_J(⁸⁵Rb₂) = 0.00953 μ_N Brooks, Anderson, et al., 1963; eqQ(⁸⁵Rb) = -1.10 MHz Logan, Cote, et al., 1952.

Spectroscopic value Tsi-Ze and San-Tsiang, 1937, extrapolation of vibrational levels in X,C,D.

Associative photoionization of rubidium vapour by atomic line absorption Lawrence and Edlefsen, 1929, Lee and Mahan, 1965, Hudson, 1965.

The state responsible for the partial predissociation (≤ ~25%) of C ¹Π_u correlates with the 5p ²P_3/2 state of Rb Brom and Broida, 1974, Feldman and Zare, 1976; see also Collins, Curry, et al., 1976 whose observations of the diffuse and sharp series of Rb in two-photon ionization of rubidium vapor through intermediate continuum states of Rb₂ include only transitions from the ²P_3/2 component.

Interference by the a ³Π_u state may be responsible for irregularities in the spectrum at 9900 cm^-1 Drummond and Schlie, 1976.

Rough estimate based on the analysis of charge exchange cross sections Olson, 1969. Theoretical calculations predict r_e = 4.45 Å Bellomonte, Cavaliere, et al., 1974.

References

Go To: Top, Gas phase 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]

Creek and Marr, 1968
Creek, D.M.; Marr, G.V., Some ultraviolet cross-section measurements on molecular alkali-metal vapours, J. Quant. Spectrosc. Radiat. Transfer, 1968, 8, 1431. [all data]

Ny-Tsi-Ze and Shang-Yi, 1938
Ny-Tsi-Ze, P.; Shang-Yi, C., Bandes d'absorption du rubidium et du cesium en presence des gaz etrangers, J. Phys. Radium, 1938, 9, 5, 169-171. [all data]

Tsi-Ze and San-Tsiang, 1937
Tsi-Ze, N.; San-Tsiang, T., Band spectra and energy of dissociation of the rubidium molecule, Phys. Rev., 1937, 52, 91. [all data]

Brom and Broida, 1974
Brom, J.M., Jr.; Broida, H.P., Laser photoluminescence and photopredissociation of Rb₂, J. Chem. Phys., 1974, 61, 982. [all data]

Kusch, 1936
Kusch, P., The band spectra of rubidium and of its combinations with other alkali metals, Phys. Rev., 1936, 49, 218. [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]

Kostin and Khodovoi, 1973
Kostin, N.N.; Khodovoi, V.A., Excitation kinetics of molecular vapor of alkali metals by intense optical radiation, Bull. Acad. Sci. USSR, Phys. Ser. Engl. Transl., 1973, 37, 69, In original 2093. [all data]

Drummond and Schlie, 1976
Drummond, D.L.; Schlie, L.A., Spectra and kinetics of the Rb₂ molecule, J. Chem. Phys., 1976, 65, 2116. [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]

Granneman, Klewer, et al., 1976
Granneman, E.H.A.; Klewer, M.; Nygaard, K.J.; van der Wiel, M.J., Two-photon ionization of Cs₂, Rb₂ and RbCs using an Ar-ion laser, J. Phys. B:, 1976, 9, 865. [all data]

Feldman and Zare, 1976
Feldman, D.L.; Zare, R.N., Evidence for predissociation of Rb₂^*(C¹Π_u) into Rb*(²P_3/2) and Rb(²S_1/2), Chem. Phys., 1976, 15, 415. [all data]

Tam and Happer, 1976
Tam, A.C.; Happer, W., Polarization of laser-excited fluorescent lines from ⁸⁵Rb₂ and ⁸⁷Rb₂ molecules, J. Chem. Phys., 1976, 64, 4337. [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]

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]

Lawrence and Edlefsen, 1929
Lawrence, E.O.; Edlefsen, N.E., The photo-ionization of the vapors of caesium and rubidium, Phys. Rev., 1929, 34, 233. [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]

Hudson, 1965
Hudson, R.D., Measurements of the molecular absorption cross section and the photoionization of sodium vapor between 1600 and 3700, J. Chem. Phys., 1965, 43, 1790. [all data]

Collins, Curry, et al., 1976
Collins, C.B.; Curry, S.M.; Johnson, B.W.; Mirza, M.Y.; Chellehmalzadeh, M.A.; Anderson, J.A.; Popescu, D.; Popescu, I., Multiphoton ionization of rubidium, Phys. Rev. A: Gen. Phys., 1976, 14, 1662. [all data]

Olson, 1969
Olson, R.E., Determination of the difference potential from resonant charge-exchange total cross sections: analysis of Rb⁺-Rb and Cs⁺-Cs, Phys. Rev., 1969, 187, 153. [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, 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
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