Photodissociation and photodetachment of molecular negative ions. III. Ions formed in CO2/O2/H2O mixtures

Abstract

Total photodestruction cross sections for O2−, O3−, O4−, O2−⋅H2O, CO4−, CO3−, and CO3−⋅H2O have been measured over the range from 6950 to 4579 Å (1.78–2.71 eV). In most cases the photodestruction of these ions can be attributed to specific photodissociation or photodetachment processes. The ions HCO3− and HCO3−⋅H2O have also been investigated, and upper limits determined for their total photodestruction. The experiments were performed using a drift tube mass spectrometer coupled with an argon ion laser and a tunable dye laser. The cross section values vary from 2×10−20 to 1×10−17 cm2, and in most cases photodissociation is the predominant process. In CO3− and O3− evidence is found for bound, predissociating excited states.