Electron coincidence spectroscopy of O2

The binding energy spectra and momentum distributions for the valence orbital transitions of molecular oxygen have been obtained using the (e,2e) reaction at total electron energies of 400 and 1200 eV. The outer πsub(g) orbital is found to have a wave-function which is significantly more extended in momentum space than that of the more-tightly bound πsub(u) orbitals. This is interpreted as a consequence of the single occupancy of the anti-bonding πsub(g) orbitals. Peaks at 39 and 47 eV are assigned to 4sup(,)2Σ-sub(g) ion states on the basis of the observed momentum distributions. The momentum distribution and observed intensity for the 32.5 eV transition supports the assignment of 2PIsub(u) for this ion state. The measured relative strengths for the various PIsub(u) and Σsub(u) transitions are in qualitative agreement with CI and Green's function calculations. (orig.)