Stark mapping of H2 Rydberg states in the strong-field regime with dynamical resolution.

Abstract

We have acquired spectra of high Rydberg states of molecular hydrogen in a static external field, in the energy region from below the energy at which field ionization becomes classically possible (${\mathit{E}}_{\mathit{c}}$) to well above this energy. Simultaneous spectra of ionization and dissociation were acquired, thereby allowing direct information on the excited-state decay dynamics to be obtained. We have found that states with energies below ${\mathit{E}}_{\mathit{c}}$ undergo field-induced predissociation, while states with energies well above ${\mathit{E}}_{\mathit{c}}$ decay predominantly by field ionization. Field ionization and dissociation compete effectively as decay channels for states with energies in a restricted region just above ${\mathit{E}}_{\mathit{c}}$. Comparison of our ionization spectra to the results of a single-channel quantum-defect theory Stark calculation shows quantitative agreement except near curve crossings, indicating that inclusion of different core rotational state channels will be required to properly account for coupling between the Stark states. Several states in the spectra undergo pronounced changes in their dynamical properties over a narrow range of field values, which we interpret as being due to interference cancellation of the ionization rates for these states.