Channel coupling and shape resonance effects in the photoelectron angular distributions of the 3 sigma g-1 and 2 sigma u-1 channels of N2.

Abstract

We report measurements of photoelectron angular distributions for the 3${\ensuremath{\sigma}}_{g}^{\mathrm{\ensuremath{-}}1}$ and 2${\ensuremath{\sigma}}_{u}^{\mathrm{\ensuremath{-}}1}$ photoionization channels of ${\mathrm{N}}_{2}$ from their thresholds up to 35 and 37.5 eV, respectively. The asymmetry parameter \ensuremath{\beta} for the 2${\ensuremath{\sigma}}_{u}^{\mathrm{\ensuremath{-}}1}$ channel exhibits a broad dip in the range h\ensuremath{\nu}\ensuremath{\sim}27--32 eV that was recently predicted theoretically to arise from shape-resonance-enhanced continuum-continuum coupling between the 3${\ensuremath{\sigma}}_{g}^{\mathrm{\ensuremath{-}}1}$ and 2${\ensuremath{\sigma}}_{u}^{\mathrm{\ensuremath{-}}1}$ ionization channels. The \ensuremath{\beta} parameter for the 3${\ensuremath{\sigma}}_{g}^{\mathrm{\ensuremath{-}}1}$ channel exhibits a prominent feature at h\ensuremath{\nu}\ensuremath{\sim}23 eV, which is tentatively attributed to the autoionization of a doubly excited valencelike state. Otherwise, the gross shape of the 3${\ensuremath{\sigma}}_{g}^{\mathrm{\ensuremath{-}}1}$ \ensuremath{\beta} curve is in good agreement with independent-electron calculations, which realistically reflect the influence of the well-known ${\ensuremath{\sigma}}_{u}$ shape resonance in this channel.