Rotational Branching Ratios inN2+: Observation of Photon Energy Dependence by Photoelectron Spectroscopy

Abstract

Rotational line profiles have been studied as a function of photon energy by use of photoelectron spectroscopy. The relative squared multipole moment matrix elements of the $X^{1}\ensuremath{\Sigma}_{g}^{+}(\ensuremath{\nu}\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}0)\ensuremath{\rightarrow}X^{2}\ensuremath{\Sigma}_{g}^{+}(\ensuremath{\nu}\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}0)$ transition of ${\mathrm{N}}_{2}$ have been determined from the relative intensities of rotational branches for photon energies between 23 and 65 eV. The relative intensities, and hence the multipole moment matrix elements of the rotational branches, are clearly dependent on photon energy. This non-Franck-Condon-like behavior can be explained by a shape resonance in the $3{\ensuremath{\sigma}}_{g}\ensuremath{\rightarrow}k{\ensuremath{\sigma}}_{u}$ ionization channel.