SELECTIVE RESONANCE POPULATION IN EELS OF PHYSISORBED O2

We have observed low-energy electron scattering via two different transient negative-ion states ((4)SIGMA(u) and (2)PI(u)) in the same phase of O2 physisorbed on graphite. Resonant electron scattering via either of the two states can be highlighted by choice of a particular scattering geometry. The results manifest the distinctive symmetry of each negative-ion state, to which the incident and emitted electron wavefields couple. We find no evidence that the interaction of the O2 molecule with the substrate quenches either molecular resonance.