Dissociative excitation ofHeH+by electron impact

We report the results of an ab initio variational treatment of electron-impact cross sections for the process ${\mathit{e}}^{\mathrm{-}}$+${\mathrm{HeH}}^{+}$→${\mathit{e}}^{\mathrm{-}}$+${\mathrm{He}}^{+}$+H for electron energies between 21 eV, the threshold for excitation of the dissociative 1 ${}_{}{}^3{}_{}{}^{}\mathrm{\Sigma }_{}^{+}{}_{}{}^{}$ state, and 26 eV, corresponding to the excitation energy of the first ${}_{}{}^1{}_{}{}^{}\mathrm{\Sigma }_{}^{+}{}_{}{}^{}$ excited state. The calculations, which were carried out using a recent modification of the complex Kohn method, employed accurate correlated target wave functions, as well as ab initio optical potentials to incorporate the effect of closed channels. The fixed-nuclei excitation cross sections were found to be dominated by a series of sharp resonance structures. However, when the cross sections are averaged over the Franck-Condon envelope of the ground vibrational state, these sharp features are no longer seen. We conclude that the recent experiments that report structure in the ${\mathrm{HeH}}^{+}$ dissociation cross section cannot be explained within the context of traditional adiabatic-nuclei theory.