Generalized oscillator strengths and integral cross sections for the valence-shell excitations of oxygen studied by fast electron impact

Abstract

The generalized oscillator strengths and differential cross sections for electron-impact excitation of the ${A}^{\ensuremath{'}} {}^{3}{\ensuremath{\Delta}}_{u}$, Schumann-Runge continuum, and $E {}^{3}{{\ensuremath{\Sigma}}_{u}}^{\ensuremath{-}}({\ensuremath{\nu}}^{\ensuremath{'}}=0,1)$ states of oxygen have been determined at an incident electron energy of 2.5 keV. Good agreement is found between the present generalized oscillator strengths of the Schumann-Runge continuum and $E {}^{3}{{\ensuremath{\Sigma}}_{u}}^{\ensuremath{-}}({\ensuremath{\nu}}^{\ensuremath{'}}=1)$ states and the previous ones measured at higher impact energies, which indicates that the first Born approximation is satisfied at an impact energy of 400 eV. However, the large difference between the present generalized oscillator strengths of the ${A}^{\ensuremath{'}}{{}^{3}\ensuremath{\Delta}}_{u}$ and $E {}^{3}{{\ensuremath{\Sigma}}_{u}}^{\ensuremath{-}}({\ensuremath{\nu}}^{\ensuremath{'}}=0)$ states and the previous ones is observed, and the possible reasons are discussed. The $\mathit{BE}$-scaled (binding energy $B$ and excitation energy $E$) or $\mathit{BEf}$-scaled ($B$, $E$, and $f$ values) integral cross sections for the ${A}^{\ensuremath{'}}{{}^{3}\ensuremath{\Delta}}_{u}$, Schumann-Runge continuum, and $E {}^{3}{{\ensuremath{\Sigma}}_{u}}^{\ensuremath{-}}({\ensuremath{\nu}}^{\ensuremath{'}}=0,1)$ states from its threshold to 5 keV were calculated based on the present generalized oscillator strengths. The present scaled integral cross sections are in good agreement with the previous ones measured at the moderate impact energies except for that of the ${A}^{\ensuremath{'}}{{}^{3}\ensuremath{\Delta}}_{u}$ state.