Quantum scattering studies of collisional energy transfer from highly excited polyatomic molecules: A bend-stretch model of He + CS₂

We present the results of an accurate quantum scattering study of collisional energy transfer in a bend-stretch model of the He + CS₂ system, considering energies up to 45kcal/mol. These results are generated using a coupled channel method, with vibrational eigenfunctions obtained from a discrete variable representation method. Detailed comparisons with the results of classical trajectory calculations are performed so as to assess classical/quantum correspondence for energy transfer moments, and for the energy transfer probability distribution function. We find good agreement of the energy averaged first moments over a wide range of molecular vibrational energies. The second moments, as well as 〈ΔE〉_up and 〈ΔE〉_down show less quantitative agreement. The quantum energy transfer distribution functions show considerable mode-specific behavior, but the overall envelope is approximately exponential at large |ΔE\ with a broad spike near |ΔE| = 0. We analyze this behavior in terms of contributions from individual state-to-state transition probabilities. The corresponding classical distribution functions are very similar, showing better correspondence than was found for other models with smaller state densities.