IR photodissociation spectroscopy of O4+, O6+ and O8+ cluster ions

O4+ and larger (O2)n+ cluster ions are produced in a pulsed discharge source and studied with time-of-flight mass spectrometry and infrared laser photodissociation spectroscopy. The infrared laser photon energies used allow bracketing of the cluster dissociation energies. Sharp resonant structure is detected for each of these ions in the region of the O–O stretching vibrations and also at higher frequencies corresponding to combination bands. Although previous matrix isolation spectroscopy on O4+ found evidence for both trans-bent and rectangular isomers of this ion, the gas phase IR spectrum only contains bands assigned to the rectangular isomer. O6+ has a distinctive IR spectrum unlike that for O4+, indicating that it is not simply a solvated O4+ species, while O8+ has the signature of a solvated O6+ ion.