The energetic thresholds for ion-pair photodissociation of diatomic oxygen $[{\mathrm{O}}_2+h\nu \to {\mathrm{O}}^{+}+{\mathrm{O}}^{-}({}_{}{}^2{}_{}{}^{}P_{3/2}^{}{}_{}{}^{},{}_{}{}^2{}_{}{}^{}P_{1/2}^{}{}_{}{}^{}\left)\right]$ were measured using a novel technique. The technique depends on the production and selective detection of highly vibrationally excited ion-pair states which last for at least $5\mu \mathrm{s}$ following single photon excitation from the ground electronic state of $O_2$. These ion-pair states are analogous to Rydberg states, and they may be dissociated by an electric field in a similar manner to the field ionization of high principal quantum number Rydberg states, allowing for their selective detection.

• Received 15 July 1997

DOI:https://doi.org/10.1103/PhysRevLett.79.3154