# Hyperfine excitation of HCl by He (Lanza et al, 2012)

Display rate coefficients as : Display rate coefficients graphically : Data information :
• HCl initial level labelled from 2 to 40
• HCl final level labelled from 1 to 39
• He initial level labelled from 1 to 1
• He final level labelled from 1 to 1
• 8 temperatures between 10 K and 300 K
• Units : cm3 s-1

HCl

He

HCl

N/A

Reduced Mass = 3.6067 a.m.u.

### References :

None

Three 3D surfaces were calculated, using the CCSD(T) level of theory, with aug-cc-pVTZ, aug-cc-pVQZ and aug-cc-pV5Z basis sets. These calculations were performed at 43 fixed intermolecular distances, R, in the range 2.5-50 a0; and at 5 HCl intramolecular distances, i.e. 2.00, 2.25, 2.41, 2.70 and 3.10 a0. The angular dependence was described along 19 angles, for a total of 4085 ab initio points. The basis set superposition error (BSSE) was corrected at all geometries with the Boys and Bernardi counterpoise procedure (Boys and Bernardi 1970). The interaction energy in the complete basis set (CBS) limit, ECBS, was then recovered from these 3 PES, by inverting the system (Peterson et al, 1994 ; Feller & Sordo, 2000): ; with X = 3,4 or 5. Mid-bond functions were omitted from the CCSD(T) calculations due to the subsequent CBS extrapolation.

The 3D PES was fitted according to the expansion proposed by Werner et al., 1989. The fitting procedure was found to provide a good representation of the ab initio points, with differences inferior to 1% on the whole grid (i.e. with an agreement better than ~0.3 cm-1 at the global minimum located at R ~ 6.3 a0). The 2D PES used in the dynamical treatment was then obtained by setting the HCl intramolecular distance to its value averaged over the fundamental vibration mode, i.e. rHCl = 2.43 a0.

### References :

Close-coupling (CC) calculations are performed for total energies ET < 3000 cm-1. The parameters of the integrator were adjusted to insure a good convergence of the highest cross sections, i.e. with an accuracy better than 0.001 for inelastic transitions.

Hyperfine cross sections are obtained in a two step procedure. First, CC calculations are performed just taking into account the rotational energy levels of HCl, which leads to obtain elements of the scatering matrix, SJ(jl,j'l'). The hyperfine structure is subsequently introduced and the scattering matrix elements are recoupled according to the methodology described by Corey & McCourt 1983. This method is independent of the exact values of the hyperfine energy levels (rotational energies are assumed), which entails that de-excitation cross sections are identical for both H35Cl and H37Cl, since the two chlorine isotopes have the same nuclear spin.

### References :

0.2 to 3000 cm-1

The number of HCl rotational states was adjusted to ensure convergence and include at least 4 closed rotational levels.

Better than a few % for the current PES.

## Presentation

Hyperfine de-excitation rate coefficients are provided among the first 11 rotational levels of HCl (up to j=10), for collisions with He and for temperatures in the range 10-300K. Either the 35Cl and 37Cl nuclei have nuclear spins I=3/2, that split every rotational levels in 4 hyperfine levels for j>1. Rate coefficients thus consider a total of 40 hyperfine levels and apply to both H35Cl and H37Cl isotopologues.

## References

NB : the main reference is displayed in red