Photoelectron angular distributions beyond the dipole approximation: A computational study on the N2 molecule

Contributions of the first-order nondipole terms to the photoelectron angular distributions from randomly oriented nitrogen molecules have been calculated in the framework of density functional theory and by employing a single centre expansion for the bound and continuum wavefunctions. Both valence and inner-shell ionizations have been considered in a photon energy range from threshold up to 2000 eV. Our results agree reasonably with calculations based on the random phase approximation and with the experimental data available. Our results for core ionizations confirm the most recent experimental finding of rather small nondipole effects in the near-threshold range. However, nondipole terms turn out to be quite large, even at the threshold, when individual contributions from the 1σ-1 g and 1σ-1 u ionization channels are considered. Strong interference effects leading to high-energy oscillations in the dipole and nondipole asymmetry parameters are satisfactorily explained within the Cohen-Fano model.