Theoretical studies in photoelectron spectroscopy: Extraction of dynamical and structural information from the angular distributions for oriented or rotationally resolved unoriented molecular samples

Abstract

We analyze the angular distributions of molecular photoelectrons for three different experimental situations: (i) photoionization in unoriented samples for rotationally unresolved transitions, (ii) photoionization in unoriented samples for rotationally resolved transitions, and (iii) photoionization in oriented samples. It is known that (iii) provides a means of determining the molecular orientation relative to the direction of polarization of the incident light and a probe of the anisotropy of the initial molecular orbital greater than that of (i). We show that (ii) also provides a probe of molecular orbital anisotropy greater than that of (i) and a probe of dynamical effects such as ’’l spoiling’’ and the penetration of waves of higher l into the inner regions of the molecular field greater than that of (i) or (iii). Calculations are carried out for the photoionization of H₂, for which experimental results exist for processes (i) and (ii). Since molecular orbital anisotropy and the above mentioned dynamical effects are small in H₂, it is a good example for the study of enhanced molecular effects available in the angular distribution for process (ii). However, the anisotropy of H₂ (and in the field of H⁺₂) is sufficiently small that the information in the angular distribution for process (iii) is overwhelmingly geometrical rather than dynamical or structural.