Classical Scattering of an Atom from a Diatomic Rigid Rotor

Abstract

Collisions between an atom and a rotating rigid linear molecule were examined by computer integration of the classical equations of motion. An anisotropic potential consisting of a Lennard‐Jones (6, 12) function multiplied by [1+aP₂(cosγ)] was used in most of the calculations (γ is the angle between the atom and the axis of the molecule). The deviation in the scattering angle caused by the anisotropy of the potential energy was found to be small and approximately proportional to a, the asymmetry parameter. The deviations were large enough, however, to distort severely the differential cross section in the rainbow scattering region. The angular‐momentum transfer was found to be appreciable (in the range ±10 ℏ) over a wide region of impact parameters extending well outside the repulsive core. For moderately heavy molecules a good approximation to the scattering angle and the angular‐momentum transfer was obtained from a ``flywheel'' model which assumes that the molecule rotates independently of the collision and calculates the effect of the resulting time‐dependent perturbation on the trajectory of the atom. Similarly, for light molecules it was found that the angular‐momentum transfer could be approximated by evaluating the time‐dependent perturbation of the molecular rotation caused by the atom moving in a trajectory calculated from the spherically symmetric part of the potential.