Observation of site-specific electron emission in the decay of superexcited O-2

The photodissociation of superexcited O-2* to O(P-3) and O*([P-2(0)]3d '') atoms, with subsequent autoionization to O+(D-2(0)) + e(-)(0.16 eV) at 22.36 eV photon energy, was studied by a new method: angle resolved photoelectron-photoion coincidence spectroscopy. A position-sensitive detector was used to measure the three components of the fragment ion velocity. When the excited atom autoionizes it emits an electron preferentially along the photodissociation axis, with a 12% greater probability to be emitted away from the recessing ground-state atom than towards the latter, pointing to possible intramolecular scattering of the electron on its way out.