Photoelectron Diffraction from Valence States of Oriented Molecules

The angular distribution of photoelectrons emitted from valence states of oriented molecules is investigated. Theprinciples underlying the angular pattern formation are explained in terms of photoelectron wave interference, caused byinitial state delocalization and final state photoelectron scattering. Computational approaches to photoelectronspectroscopy from molecules are briefly reviewed. Here a combination of molecular orbital calculations for the initialstate and multiple scattering theory for the photoelectron final state is used and applied to the 3σ and 4σ orbitals ofnitrogen and the highest occupied molecular orbital of pentacene. Appreciable perpendicular emission and circulardichroism in angular distributions is found, two effects that cannot be described by the popular plane waveapproximation to the photoelectron final state.