Photon-stimulated desorption of negatively charged ions from condensed ${\mathrm{O}}_2$ is observed in the 17–42-eV photon energy range. Two classes of photon-stimulated charge-transfer processes, i.e., resonant processes via the formation of highly excited states of the condensed molecules and nonresonant processes involving energetic photoelectrons, are considered to account for these observations.

• Received 19 March 1991

DOI:https://doi.org/10.1103/PhysRevLett.67.1844