Quantum Scattering Studies of Collisional Energy Transfer from Highly Excited Polyatomic Molecules: Collinear He + CS₂ at Energies up to 92 kcal/mol

We present the results of an accurate quantum scattering study of collisional energy transfer in the collinear He + CS₂ system, considering energies up to 92 kcal/mol. These results are generated using a coupled channel calculation with a basis of 1000 vibrational states from a discrete variable representation calculation. 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 very good agreement of the energy averaged first moments over a wide range of molecular vibrational energies, provided that the translational energy is not too low (translational temperatures below 300K). The second moments, as well as 〈ΔE〉_up and 〈ΔE〉_down show poorer agreement, especially at low temperatures. The quantum energy transfer distribution functions show considerable mode-specific behavior, but the overall envelope is approximately exponential for |ΔE| > 2 kcal/mol, with a faster than exponential drop for ΔE < - 20 kcal/mol and ΔE > + 5 kcal/mol, and with a broad spike for |AE| < 2 kcal/mol. All of these results accurately match the corresponding classical trajectory distributions. The connection of the shape of these distributions with the individual state-to-state probabilities is studied in detail, and it is found that much of this behavior may be connected with the probability of symmetric stretch excitation and deexcitation.