(e,e+ion) study on electron-induced dissociative ionization of O2

Abstract

Electron-induced dissociative ionization of ${\mathrm{O}}_{2}$ has been investigated by means of $(e,\phantom{\rule{0.16em}{0ex}}e+\mathrm{ion})$ spectroscopy. The linear momenta of the fragment ions have been measured in coincidence with electron energy-loss spectra for ${\mathrm{O}}_{2}$ at scattering angles of $2.{2}^{\ensuremath{\circ}}, 4.{2}^{\ensuremath{\circ}}$, and $8.{2}^{\ensuremath{\circ}}$ using an incident energy of 1.4 keV. From the analysis of the data, partial ion yield spectra have been obtained for the $B\phantom{\rule{0.16em}{0ex}}^{2}\mathrm{\ensuremath{\Sigma}}, {c\phantom{\rule{0.16em}{0ex}}^{4}\mathrm{\ensuremath{\Sigma}}+2\phantom{\rule{0.16em}{0ex}}^{2}\mathrm{\ensuremath{\Sigma}}+2\phantom{\rule{0.16em}{0ex}}^{4}\mathrm{\ensuremath{\Sigma}}}, {2\phantom{\rule{0.16em}{0ex}}^{2}\mathrm{\ensuremath{\Sigma}}+2\phantom{\rule{0.16em}{0ex}}^{4}\mathrm{\ensuremath{\Sigma}}}$, and $3\phantom{\rule{0.16em}{0ex}}^{2}\mathrm{\ensuremath{\Sigma}}$ ionization, allowing us to assess state-specific momentum-transfer dependence of the relative ionization cross sections. It has been shown that the shape resonance in the $B\phantom{\rule{0.16em}{0ex}}^{2}\mathrm{\ensuremath{\Sigma}}$ channel is substantially suppressed by the contributions of electric nondipole transitions. To get insight into the stereodynamics in the electron-${\mathrm{O}}_{2}$ collision processes, the angular distributions of the fragment ions have been examined. It has been revealed that the $(e,\phantom{\rule{0.16em}{0ex}}e+\mathrm{ion})$ cross section for the $2{\ensuremath{\sigma}}_{\mathrm{g}}\ensuremath{\rightarrow}1{\ensuremath{\pi}}_{\mathrm{g}}$ autoionization band exhibits a characteristic angular distribution reflecting the anisotropic shape of the molecular orbital to which the target electron is excited.