Dissociative and nondissociative photoionization ofH2from theE,FΣg+1excited state

Abstract

We present a theoretical study of dissociative and nondissociative photoionization of ${\mathrm{H}}_{2}$ from the $E,F^{1}\ensuremath{\Sigma}_{g}^{+}(\ensuremath{\upsilon},J=0)$ excited state for $\ensuremath{\upsilon}=0--9$ in the photon energy range $3\phantom{\rule{0.3em}{0ex}}\text{to}\phantom{\rule{0.3em}{0ex}}14\phantom{\rule{0.3em}{0ex}}\mathrm{eV}$. We have found that, for most initial $\ensuremath{\upsilon}$'s, dissociative ionization is the dominant process for photon energies well above the dissociative ionization threshold. In this photon energy range, resonance structures arising from autoionization of the ${Q}_{1}$ doubly excited states of ${\mathrm{H}}_{2}$ are observed. Cross sections differential in the energy of the remaining ${\mathrm{H}}_{2}^{+}$ ion or in the proton kinetic energy are analyzed in detail for a photon energy of $6.4\phantom{\rule{0.3em}{0ex}}\mathrm{eV}$ corresponding to the wavelength of an ArF excimer laser. Comparison of our results with the available experimental measurements is good. We show, however, that contribution of the ${Q}_{1}$ doubly excited states to the measured dissociative ionization cross section is more important than originally believed.