Photodissociation and photodetachment of molecular negative ions. II. Ions formed in oxygen

Total photodestruction cross sections for O−2, O−3, and O−4 ions have been measured over a photon energy range of 1.93–2.71 eV using a drift tube mass spectrometer coupled with an argon ion laser and a tunable dye laser. The O−2 ion is found to photodetach at these photon energies with a cross section which varies from 1.2 to 2.2×10−18 cm2. The O−3 ion photodissociates to form O− over this energy range with a cross section which varies from 0.1 to 7.3×10−18 cm2 and exhibits structure indicative of the vibrational levels of a predissociating excited state. Structure is also observed in the O−4 photodestruction cross section which varies from 1.0 to 2.2×10−18 cm2, and in the O−2 photodetachment cross section.