Differential cross-sections and energy transfer quantities in azulene/argon collisions

Abstract

Computational results on collisional energy transfer between excited and cold azulene and Ar are reported under initial conditions similar to those of crossed molecular beam experiments (Liu, Hsu, Lyu and Ni, J. Chem. Phys. 125 204309 (2006)). The in-plane scattering cross-section is asymmetric with a preference for positive angles. The out-of-plane scattering angle is symmetric in both positive and negative angles with a strong forward scattering peak. In both T → V/R dominates over V → R/T. The double differential cross-section shows a high probability for forward, then sideways and finally, backward scattering. The latter shows relatively high probability for supercollisions. Average energy transfer quantities and collisional energy transfer probability density functions, P(E,E′), are presented and results for Ar and Kr as colliders are compared. At low initial relative translational energies the up-collision branch of P(E,E′) shows a peak. This peak, which is absent at higher relative translational energies, is due to the formation of a collision complex. Special attention is paid to the role of rotational energy in the energy transfer process. Changing the rotational temperature from 0.5 K to 2000 K changes the percentage of up and down collisions as well as the values of the average energy transferred quantities. The effect of the translational energy on energy transfer is discussed. There is broad agreement between experiment and computation.