Channel coupling and shape resonance effects in the photoelectron angular distributions of the 3${\sigma }_g^{\mathrm{-}1}$ and 2${\sigma }_u^{\mathrm{-}1}$ channels of ${\mathrm{N}}_2$

We report measurements of photoelectron angular distributions for the 3${\sigma }_g^{\mathrm{-}1}$ and 2${\sigma }_u^{\mathrm{-}1}$ photoionization channels of ${\mathrm{N}}_2$ from their thresholds up to 35 and 37.5 eV, respectively. The asymmetry parameter β for the 2${\sigma }_u^{\mathrm{-}1}$ channel exhibits a broad dip in the range hν∼27–32 eV that was recently predicted theoretically to arise from shape-resonance-enhanced continuum-continuum coupling between the 3${\sigma }_g^{\mathrm{-}1}$ and 2${\sigma }_u^{\mathrm{-}1}$ ionization channels. The β parameter for the 3${\sigma }_g^{\mathrm{-}1}$ channel exhibits a prominent feature at hν∼23 eV, which is tentatively attributed to the autoionization of a doubly excited valencelike state. Otherwise, the gross shape of the 3${\sigma }_g^{\mathrm{-}1}$ β curve is in good agreement with independent-electron calculations, which realistically reflect the influence of the well-known ${\sigma }_u$ shape resonance in this channel.