Trajectory studies of collisional relaxation of highly excited CS ₂ by H₂, CO, HCl, CS₂, and CH₄

The collisional relaxation of vibrationally highly excited CS₂ by thermal ensembles of H₂, CO, HCl, CS₂, and CH ₄ is investigated theoretically using classical trajectory calculations with empirical potentials that include van der Waals and electrostatic interactions. The successive collisions method suggested by Bruehl and Schatz is shown to be an effective way to study energy transfer from vibrationally hot polyatomic molecules to molecules of a thermal bath. The average energy transferred per collision to H₂ and CO matches experimental measurements within a factor of 2, while that to CH₄ and CS₂ matches experiment within a factor of 4. These differences are consistent with combined theoretical and experimental uncertainties. Energy transfer to HCl is, however, off by as much as a factor of 7, despite our use of a potential which is realistic at long range. The energy transferred is partitioned mostly to relative translation when the collider is H₂ or CO and partly to rotation for CH₄. The energy dependence of the energy transfer and the interrelations among energy-transfer moments, including 〈ΔE_up〉, 〈ΔE_down〉, and 〈ΔE²〉, are also reported.