Dissociative attachment to rovibrationally excitedH2

Using a local-width resonant model, the cross sections for dissociative attachment of low-energy electrons to a rovibrationally excited ${\mathrm{H}}_2$ molecule in its ground electronic state are obtained. There are 294 such rovibrational levels. Only the contribution of the ${}_{}{}^2{}_{}{}^{}\Sigma _u^{+}{}_{}{}^{}$ resonant state of ${\mathrm{H}}_2^{-}$ to the attachment process is investigated. Assuming a Maxwellian distribution for electron energies, the dissociative attachment cross sections are converted into attachment rates for various rovibrational levels of ${\mathrm{H}}_2$. A significant enhancement of attachment rates occurs for endoergic reactions only, and the maximum possible rate for attachment to the ground electronic state of ${\mathrm{H}}_2$ is about ${10}^{-8\mathrm{}}$ ${\mathrm{cm}}^3$/sec. Using the same energy distribution for electrons, the average energy carried by the ${\mathrm{H}}^{-}$ ions is calculated for all possible rovibrational levels. More energetic ions are formed when the attachment process is exoergic, and even the most energetic ${\mathrm{H}}^{-}$ ions have energies less than 0.5 eV. Furthermore, the attachment rates and the average ion energy appear to depend roughly on the total internal energy and not on the exact fraction of internal energy in rotational or vibrational modes.