Differential and Integral Cross Sections for the Electron-Impact Excitation of theaΔg1andbΣg+1States ofO2

Abstract

Electron-impact energy-loss spectra of ${\mathrm{O}}_2$ have been analyzed for incident electron energies from 4 to 45 eV, scattering angles from 10° to 90°, and energy losses from 0 to 5 eV. The inelastic processes observed were the excitation of the $a{}_{}{}^1{}_{}{}^{}\Delta _g^{}{}_{}{}^{}$ and $b{}_{}{}^1{}_{}{}^{}\Sigma _g^{}{}_{}{}^{+}$ electronic states and vibrational excitation in some cases to $v^{\prime \prime }=13\mathrm{}$. The excitation cross sections at each energy were made absolute by normalizing the sum of the integral cross sections (all inelastic, ionization, and elastic) to measured electron-${\mathrm{O}}_2$ total cross sections. The differential cross sections for the $a{}_{}{}^1{}_{}{}^{}\Delta _g^{}{}_{}{}^{}$ and $b{}_{}{}^1{}_{}{}^{}\Sigma _g^{}{}_{}{}^{+}$ states show nearly isotropic behavior, as expected for optically spin-for-bidden transitions. The elastic differential cross sections are strongly forward peaked at higher energies, but become only slightly forward peaked at the lower energies. The integral cross sections for the excitation of the $a{}_{}{}^1{}_{}{}^{}\Delta _g^{}{}_{}{}^{}$ and $b{}_{}{}^1{}_{}{}^{}\Sigma _g^{}{}_{}{}^{+}$ states reach their maxima near 7 eV and are more than an order of magnitude larger than previous estimates. The integral elastic cross section reaches its maximum at around 10 eV.