Observation of the A 2Πu←X 2Πg dissociative transition in isolated O2− using mass-selected photofragmentation spectroscopy

Publisher Website
Google Scholar
Abstract
We report the observation of the A 2Πu electronically excited state of the isolated, gas phase O2− superoxide anion by photofragmentation in the range of 4.5 eV, well above the onset of the electron detachment continuum at 0.45 eV. The action spectrum of O− photoproducts displays an abrupt onset in the vicinity of the known O2− dissociation energy. Quantum yield studies indicate that the dissociative pathway is about 3% relative to the direct electron photodetachment channel. The angular distribution of the ejected O− ions reveals a primarily parallel electronic transition (β=+1.2±0.1), allowing the 2Πu identification of the excited electronic state. This state has been observed previously in fluorescence from O2− in alkali crystals at low temperature, and appears to be the same excited state invoked to account for dissociative attachment of electrons onto neutral O2..