A preliminary report is presented on experiments using fast ion-beam translational energy spectroscopy to study dissociative photodetachment and photodissociation dynamics in the small cluster ions O₄^- and O₂^-.(H₂O). Translational energy and angular distributions of coincident molecular fragments were recorded from the photodestruction of O₄^- and O₂^-.(H₂O) at 523, 349 and 262 nm. At each wavelength, the O₄^- results confirm the existence of at least two distinct channels: dissociative photodetachment ( O₄^- + hv --> O₂ + O₂ + e^-) and photodissociation ( O₄^- + hv --> O₂ + O₂^-).

Observation of strongly anisotropic angular distributions shows that dissociation occurs on the time-scale of molecular rotation in both processes. The photodissociation of O₄^- at 523 nm gives a new value for the O₂-O₂^- bond energy, D₀ = 0.39 +/- 0.05 eV. In O₂^-.(H₂O), a single dissociative photodetachment channel ( O₂^-.(H₂O) + hv --> O₂ + H₂O + e^-) is observed at all wavelengths. Angular distributions from this process are slightly anisotropic and exhibit a small wavelength dependence.