Partial cross sections and interfering resonances in photoionization of molecular nitrogen

Abstract

We present an in-depth theoretical study of ${\mathrm{N}}_{2}$ photoionization in the region between the second (${}^{2}{\mathrm{\ensuremath{\Pi}}}_{u}$) and third (${}^{2}{\mathrm{\ensuremath{\Sigma}}}_{u}^{+}$) ionization thresholds. In this region, the electronic continuum includes the Hopfield series of autoionizing states, corresponding to excitations to $ns{\ensuremath{\sigma}}_{d}$, $nd{\ensuremath{\sigma}}_{d}$, and $nd{\ensuremath{\pi}}_{g}$ molecular orbitals. Calculations have been performed by using the xchem code, which makes use of a Gaussian and B-spline hybrid basis in the framework of a close-coupling approach. We provide total and partial photoionization cross sections for all open channels, energy positions, and widths for the five lowest resonances of each series and, when resonances are well isolated from each other, Fano and Starace parameters. We also discuss how the coupling between the two series of overlapping resonances, $ns{\ensuremath{\sigma}}_{d}$ and $nd{\ensuremath{\sigma}}_{d}$, affects their energies and autoionization widths. These results show the potential of the xchem method to describe resonant photoionization in molecules.