Theoretical studies in photoelectron spectroscopy: Use of angular distribution data to deduce molecular orbital parameters. II. Calculation the angular distributions for electrons ejected from molecules of selected symmetries

Abstract

The theory of the angular distribution for molecular photoionization resulting in ejection of energetic electrons, previously formulated for the case of linear, nonpolar molecules, is extended to the case of molecules of any geometry. Calculations are performed for the angular distributions of electrons ejected from molecules of the following symmetries: C3ν (distorted CH4 as an example of a nonlinear, polar molecules), D3h (planar CH3 as an example of a nonlinear, nonpolar molecules), and Td (CH4 as another example of a nonlinear, nonpolar molecules). The initial molecules orbitals are represented as symmetry orbitals in the LCAO form, re-expanded about the carbon atom. These orbitals are in parametrized form such that the features of the angular distributions can be related to selected parameters. The ejected electron is assumed to move in a multicenter screened Coulomb field, and the set of coupled differential equations which describe its motion relative to the distance from the carbon atom is solved by consecutive use of the distorted-wave Born and Coulomb-Born approximations. At this level of approximation the effects of the molecular ionic field on the motion of the ejected electron are calculated to first order in perturbation theory, where the zeroth order motion is motion in the Coulomb potential of unit strength relative to the carbon atom. The features of the angular distribution are found to be quite sensitive to the symmetry of the molecule and therefore to molecular orbital parameters and multiplet splittings.