Absolute differential cross sections for the excitation of molecular oxygen by electron impact: Decomposition of the Schumann-Runge continuum.

Abstract

Using a crossed-beam method, we have measured electron-energy-loss spectra for the excitation of the Schumann-Runge continuum of molecular oxygen. The scattering angle and electron-impact energy ranges covered were 12\ifmmode^\circ\else\textdegree\fi{}--156\ifmmode^\circ\else\textdegree\fi{} and 15--50 eV, respectively. By means of computerized least-squares analysis, we decomposed the spectra into contributions from three superposed Gaussian line shapes. The two lowest in energy are identified as representing excitation of the ${1}^{3}$${\mathrm{\ensuremath{\Pi}}}_{\mathit{g}}$(v) and ${\mathit{B}}^{3}$${\mathrm{\ensuremath{\Sigma}}}_{\mathit{u}}^{\mathrm{\ensuremath{-}}}$(v) states. The other line shape cannot be definitively identified, but we discuss several possibilities for its meaning. Absolute differential and integrated cross sections for all three states are obtained, along with linear electronic potential-energy curves for the Franck-Condon region.