Vibrationally selected O+-O+ fragmentation of O-2 below the adiabatic double-ionization potential studied via electron-electron coincidence spectroscopy

Mechanisms for O-2 photofragmentation leading to the formation of the O+-O ion pairs, at photon energies below the adiabatic double-ionization thresh old, have been investigated using a threshold-photoelectron-photoelectron c oincidence technique. The selectivity and high efficiency of the experiment al technique have allowed the process to be followed step by step. The meas urements show that fast dissociation of a singly charged ion, followed by a tomic autoionization, is the dominant decay route in this energy region.