Classical theory of rotational rainbow scattering from uncorrugated surfaces

Abstract

A classical perturbation theory is developed to study rotational rainbow scattering ofmolecules from uncorrugated frozen surfaces. Considering the interaction of the rigidrotor with the translational motion towards the surface to be weak allows for aperturbative treatment, in which the known zeroth order motion is that of a freelyrotating molecule hitting a surface. Using perturbation theory leads to explicitexpressions for the angular momentum deflection function with respect to theinitial orientational angle of the rotor that are valid for any magnitude of theinitial angular momentum. The rotational rainbows appear as peaks both in thefinal angular momentum and rotational energy distributions, as well as peaks inthe angular distribution, although the surface is assumed to be uncorrugated.The derived analytic expressions are compared with numerical simulation data.Even when the rotational motion is significantly coupled to the translationalmotion, the predictions of the perturbative treatment remain qualitatively correct.