Wave packet study of gas phase atom–rigid rotor scattering

Abstract

The close coupling wave packet (CCWP) method has recently been extended to treat gas phase atom–diatom collisions. The total angular momentum representation reduces the complexity of the coupled wave packet equations. In this paper, the theory is extended by modifying the form of the initial packet so that, even though the (JjlM) representation is used, a single wave packet propagation provides complete information for scattering out of a particular j, mj initial rotor state with total angular momentum J. We present results of further testing the method using the Lester–Bernstein model atom–rigid rotor system for various numbers of coupled channels N, including N=25, 64, 144, 256, 969. The results for 969 channels show clearly the transition from the ‘‘l-dominant’’ regime at lower energies, where the scattering is dominated by the long-range attraction, to a more sudden regime at higher energies, where the scattering is dominated by the short-range repulsive interaction. The dependence on the final orbital angular momentum at higher energy is interpreted in terms of orbital angular momentum rainbow scattering. The results are very encouraging indicating that the wave packet method can treat gas phase collisions involving very large numbers of quantum states.