Electronic excitation in collisions of H andH+withO2

Abstract

The 115-750-nm radiation produced in collisions of 1.5-25-keV ${\mathrm{H}}^{+}$ and H with ${\mathrm{O}}_{2}$ has been studied in an atomic-beam experiment under thin-target conditions. For both ion and neutral impact, the ($b^{4}\ensuremath{\Sigma}_{g}^{\ensuremath{-}}\ensuremath{-}a^{4}\ensuremath{\Pi}_{u}$) first-negative ($1N$) and ($A^{2}\ensuremath{\Pi}_{u}\ensuremath{-}X^{2}\ensuremath{\Sigma}_{g}^{+}$) second-negative ($2N$) band systems of ${\mathrm{O}}_{2}^{+}$ are the most intense spectral features. Also observed are several emissions from excited states of O and ${\mathrm{O}}^{+}$. Relative cross sections for individual bands of the ${\mathrm{O}}_{2}^{+}$ $1N$ system, obtained by deconvolution of overlapped features in several vibrational sequences, were used to show that the vibrational population $P({v}^{\ensuremath{'}})$ for ${\mathrm{O}}_{2}^{+}$ $b^{4}\ensuremath{\Sigma}_{g}^{\ensuremath{-}}$ formed in both ${\mathrm{H}}^{+}$ and H impact is in good agreement with the predictions of a simple Franck-Condon mechanism over the 2-25-keV energy range. Total cross sections for formation of ${\mathrm{O}}_{2}^{+}$ $b^{4}\ensuremath{\Sigma}_{g}^{\ensuremath{-}}$ in ${\mathrm{H}}^{+}$ and H impact, determined from the latter results by normalization to previous proton-impact data, are in good agreement with values calculated via application of the semiempirical procedure developed recently by Edgar et al. For both projectiles the semiempirical approach gives a good prediction of the energy dependence and an adequate prediction of the magnitude of the cross sections for formation of ${\mathrm{O}}_{2}^{+}$ $A^{2}\ensuremath{\Pi}_{u}$ determined by integration of measured $2N$ band intensities.