Ionization and dissociation ofH2in a static electric field: Levels near the ionization threshold

We have made high-resolution measurements of the photoionization and photodissociation spectra of molecular hydrogen in the energy region near the first ionization limit in a strong, static, external electric field. We find that below the classical field-ionization energy ${\mathit{E}}_{\mathit{c}}$=-2 √F electric-field-induced predissociation is a dominant decay mechanism for many of the highly excited Stark components, while above the classical field-ionization energy there is a competition between field-induced ionization and dissociation. We have also observed forced autoionization of the (1sσ7pσ) ${}_{}{}^1{}_{}{}^{}\mathrm{\Sigma }_{\mathit{u}}^{+}{}_{}{}^{}$(ν=1, J=1 and 2) levels through their coupling with the structured continuum of highly excited Stark states, leading to enhanced ionization and dissociation through those Stark states that are nearly degenerate with them.