Calculation of Dissociative Attachment in HotO2

The very striking temperature dependence of the dissociative attachment cross sections found experimentally in ${\mathrm{O}}_2$ has been reproduced by a semi-empirical calculation, assuming a Maxwell distribution of vibrational ($v$) and rotational ($r$) states. A recently derived expression for the cross section ${\sigma }_{v,r}$ is used, and the final-state potential curve of $\mathrm{O}_2^{}{}_{}{}^{-}$ is parametrized to fit the experiments. The temperature shift is found to be caused by the effect on excited vibrational states of the rapidly varying "survival probability," a measure of the competition between auto-ionization and dissociation. Byproducts of the calculation are the potential curve for the final dissociating state of $\mathrm{O}_2^{}{}_{}{}^{-*}$, together with an estimate of its auto-ionization width ${\Gamma }_a\mathrm{}\left(R\right)\mathrm{}$, and also the contribution of this state to the total cross section for electron-energy loss to vibrational excitation and dissociation.