Angular distributions of electrons from resonant two-photon ionization of molecules

Abstract

A phenomenological theory is developed for the angular distribution of photoelectrons produced by resonant two-photon ionization of diatomic molecules. The physical situation described by the theory is optical excitation of the target molecule to a real electronically excited intermediate state followed by ionization induced by absorption of a second photon of a frequency different from the first. If experiments include all possible polarizations, up to ten independent phenomenological parameters can be obtained. The phenomenological parameters are given in terms of microscopic physical parameters appropriate for diatomic molecules, transition amplitudes to the various final state channels for the photoelectron expressed in a molecule-fixed coordinate system. The form of this reduction depends upon which Hund’s coupling case is used to describe the molecular states and upon whether fine structure is resolved in the photoelectron spectrum. The theory is illustrated for a few specific examples.