Theory of two-photon autoionization ofH2

We present a model calculation for two-photon autoionization of ${\mathrm{H}}_2$ to the $X{}_{}{}^1{}_{}{}^{}\Sigma _g^{}{}_{}{}^{}$ state of ${\mathrm{H}}_2^{+}$. The theory is based on a formulation that allows for strong-field effects. It is shown that, as a result of such effects, the autoionization profile will in general exhibit qualitatively new behavior at laser intensities needed for two-photon ionization. The magnitude of these effects depends significantly on the presence of resonance with intermediate states. The notion of autoionization width and $q$ parameter are generalized to include this new behavior. Detailed calculations are reported for intensity effects on the line profile, the role of intermediate resonances, and the separate contribution of the vibrational states of ${\mathrm{H}}_2^{+}$ as final states. The feasibility of observation with currently available sources is discussed.