Non-Franck-Condon distribution of final states in photoionization of ${\mathrm{H}}_2$(${\mathrm{C}}^1$${\mathrm{\Pi }}_{\mathrm{u}}$)

A striking feature of recent measurements of the photoionization of ${\mathrm{H}}_2$(${\mathrm{C}}^1$ ${\mathrm{\Pi }}_{\mathrm{u}}$) is that the distribution of final vibrational states of ${\mathrm{H}}_2$ ${\mathrm{}}^{+}$ differs significantly from the predictions of the Franck-Condon approximation. A theory is presented that accounts for these measurements. The essential physical mechanism is photoexcitation of the dissociating, autoionizing ${}_{}{}^1{}_{}{}^{}\mathrm{\Pi }_{\mathrm{g}}^{}{}_{}{}^{}$ electronic state of ${\mathrm{H}}_2$, followed by competition between dissociation of the nuclei (leading to ${\mathrm{H}}^{\mathrm{*}}$+H) and electronic autoionization (leading to ${\mathrm{H}}_2$ ${\mathrm{}}^{+}$+e).