Double photoionization of polyatomic molecules by arbitrarily polarized light: theory

Abstract

This paper develops a theoretical framework suitable for studying simultaneous ejection of two electrons following the absorption of a single photon by a molecule belonging to one of the 32 point groups. The ionizing electromagnetic radiation is assumed to have any arbitrary polarization. Both photoelectrons are analysed in terms of their energies as well as directions of propagation. The transformation properties of the molecular point symmetry group are used to their full advantage to reduce the various expressions obtained herein to their simplest possible forms. The ionization amplitude is thus shown to decompose into a sum of transitions each involving a final state wavefunction belonging to the irreducible representations of the point group of the molecular target. Molecules with both a random or a fixed orientation in space have been considered. The results obtained herein can therefore be used to study double photoionization of any point symmetry molecule in either its gaseous phase or oriented on liquid and solid surfaces. The analysis is general in that it is independent of any particular dynamical models for the description of photoionization. The present results show that such double photoionization experiments are richer sources of information, specifically on interaction between adsorbed molecules and surfaces and on the geometry of the adsorbate–substrate system, in addition to the electron–electron correlation, than their counterpart experiments on single photoionization. Various possible cases and several observables are discussed.