Autoionization of nonpenetrating Rydberg states in diatomic molecules

Molecular Rydberg states with l>2 exhibit essentially no core penetration, and so interact with the molecular ion core principally through its polarizability and multipole moments. If the core is sufficiently excited vibrationally or rotationally, these interactions can give rise to autoionization. The ionization rates are readily calculable using methods developed previously to calculate the energy-level structure of these states. Detailed calculations are described for the Rydberg nf states of ${\mathrm{H}}_2$. Since the structure of nonpenetrating Rydberg states varies only slightly from molecule to molecule, many of these results are readily generalized. Several significant conclusions can be drawn. The first is that autoionization usually dominates radiative decay when it is energetically possible, even for states with rather high l. Second, rotational autoionization is typically more rapid than vibrational autoionization even in cases where both can occur. However, the rates vary tremendously with the total angular momentum N. Finally, the effects of quantum interferences affect the rates significantly, so it is important to perform a detailed calculation using accurate wave functions. Preliminary results of an experiment on the autoionization of the nf states of the ${\mathrm{H}}_2$ molecule are presented and compared with ab initio calculations. The good agreement suggests that this simple model suffices to account for the principal decay processes of these states.