Mixed Quantum−Classical Scattering Dynamics of CF3Br

Abstract

The vibrational excitation of CF3Br scattering from graphite has been studied using mixed quantum−classical methods. A previously investigated 2D model for the intramolecular degrees of freedom [Back, A.; Markovic, N. Chem. Phys. 2002, 285, 233] has been extended to 3D including all vibrations of a1 symmetry, improving the dynamical description of the umbrella mode. We investigate the details of the excitation process for a few selected initial conditions as well as the general effect of surface temperature for ensembles of randomly sampled trajectories. Quantum results are obtained from 3D wave packet propagations and calculations based on the time-dependent Gauss−Hermite discrete variable representation method. When the quantum data are compared with classical results it is confirmed that quantization of the internal degrees of freedom does indeed have a very small effect for the present system. Considering vibrational excitation from the ground state, almost perfect agreement between quantum and classical calculations is found, provided that the classical trajectories are initialized without vibrational energy.