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Rotational excitation of CS by H2, 10K < T < 100K, 13 lowest levels (Green & Chapman, 1978)



Display rate coefficients as : Display rate coefficients graphically : Data information :
  • CS initial level labelled from 1 to 13
  • CS final level labelled from 1 to 13
  • H2 initial level labelled from 1 to 1
  • H2 final level labelled from 1 to 1
  • 6 temperatures between 10 K and 100 K
  • Units : cm3 s-1

CS

H2


CS


N/A

Reduced Mass = 1.828

References :

None

PES is given in Green et al, 1978. It is adapted fom a Gordon and Kim (1972; Green et al 1975) electron gas model for CS-He, treating the CS molecule as a rigid rotor (re = 2.8996 Bohr). V(R,theta) for R varying between 3.0 and 10.0 (step 0.5) Bohr and 11 orientations. Angle dependence fitted to 8 Legendre expansion terms (minimization of rms deviation). For R>8 a0, the lowest 4 terms are modified to join smoothly with asymptotic electrostatic interaction (Buckingham, 1967, Green & Thaddeus, 1976), with molecular parameters:

Polarizability (Angst3) H2 : 0.79 [ra]
Ionization potential (eV) H2 : 15.6 [ra]
Dipole (Debye) CS: 1.96 [rc]
Quadrupole (10-26 esu cm2) CS: 2.0 [rb]
Polarizability (Angst3) CS: 6.0 [ra, rb]
Polarizability perpendicular (Angst3) CS: 1.6 [ra, rb]
Polarizability parallel (Angst3) CS: 2.8 [ra, rb]
Ionization potential (eV) CS: 12.4 [rb]

[ra] Hirschfelder et al, 1954 :
"Molecular Theory of Gases and Liquids", (NY: Wiley)
[rb] Estimated from HF calculations + comparison with similar molecules
[rc] Mockler and Bird, 1955, Phys. Rev., vol. 98, p. 1837

References :


1978's paper : Close Coupling (CC) is used below 50 cm-1 and Coupled states (CS) above 50 cm-1. Some comparisons between CC and CS are presented for few transitions, showing differences about 25% at 50 cm-1.
1992 's paper : they claim that CS calculations are used (no indication whether low energy calculations have been carried out with close coupling calculations)

References :

None

No indication is given in 1978's paper.
In 1992's paper a large number of energies up to 1800K is used.

1978's paper : CC/B7 E < 50 cm$-1 ; CS/B16 50 <150 cm$-1 ;CS/B20 for E>150 cm$-1.
1992's paper : as many as 36 rotational levels are used to ensure convergence (no detailed information).
Note : Bn means a basis set up to j=n

A factor of 2 owing to the CS approximation and to the PES, and the 1992 authors claim that an additionnal factor of 2-3 is expected for rates with J(H2) = 1.
It is claimed in 1992's paper that 1978 and 1992 results agree well in the overlapping region.
Note MLD : it is not completly true,in particular there is nearly of factor 2 of difference for the  j=0\rightarrow j=1 transition at 20K. The difference decreases when temperature increases. Only the lowest transitions show differences (not all of the same magnitude).
We expect the 1992's results to be of better quality, in particular having more energy points.

Presentation

see link to http://www.giss.nasa.gov/data/mcrates#cs
The rate coefficients provided here are those of Green & Chapman, 1978. They calculated rate coefficients between 10K and 100K between the lowest 13 rotational levels.

Turner & al,1992 used the same theoretical modeling as the 1978 paper and extended the calculations to transitions between the first 21 levels and to temperature between 20K and 300K. Turner & al, 1992 results are provided in a separate dataset


References

NB : the main reference is displayed in red
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Status Version Date
Published 1 2005-07-01