Aligning symmetric and asymmetric top molecules via single photon excitation

Abstract

The theory developed by Zare [Ber. Bunsenges. Phys. Chem. 86, 422 (1982)] for using electric-dipole-allowed photoexcitation with linearly polarized light to align linear and symmetric top molecules via parallel transitions is extended to include perpendicular transitions, as well as the alignment of asymmetric tops via a-, b-, or c-type transitions. Analytical expressions for the spatial distribution of a symmetric top figure axis following a parallel or perpendicular transition are presented. A prescription is developed for determining the spatial distribution of each principal axis of an asymmetric or symmetric top following parallel or perpendicular type transitions. The degree of alignment obtainable via photoexcitation for symmetric and asymmetric tops is discussed, with the somewhat surprising result that all three principal axes of an asymmetric top can be highly aligned via photoexcitation. A simple computer program for calculating the degree of alignment of each principal axis of a symmetric or asymmetric top following an a-, b-, or c-type transition is described and made available.