Electronic excitation in collisions of H andH+withO2

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 ($b{}_{}{}^4{}_{}{}^{}\Sigma _g^{-}{}_{}{}^{}-a{}_{}{}^4{}_{}{}^{}\Pi _u^{}{}_{}{}^{}$) first-negative ($1N$) and ($A{}_{}{}^2{}_{}{}^{}\Pi _u^{}{}_{}{}^{}-X{}_{}{}^2{}_{}{}^{}\Sigma _g^{+}{}_{}{}^{}$) 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 $P\left(v^{\prime }\right)$ for ${\mathrm{O}}_2^{+}$ $b{}_{}{}^4{}_{}{}^{}\Sigma _g^{-}{}_{}{}^{}$ 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 ${\mathrm{O}}_2^{+}$ $b{}_{}{}^4{}_{}{}^{}\Sigma _g^{-}{}_{}{}^{}$ 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 ${\mathrm{O}}_2^{+}$ $A{}_{}{}^2{}_{}{}^{}\Pi _u^{}{}_{}{}^{}$ determined by integration of measured $2N$ band intensities.