KINETIC-ENERGY DISTRIBUTIONS OF O- PRODUCED BY DISSOCIATIVE ELECTRON-ATTACHMENT TO PHYSISORBED O-2

We report measurements of the kinetic energy (Ek) distributions of O- produced by low-energy electron impact (5.519.5 eV) on disordered multilayers of O2 physisorbed on a polycrystalline Pt substrate. The results confirm that dissociative electron attachment (DEA) proceeds via the formation of the u2, g+2(I), and x+2(II) (x=g and/or u) states of O2-*. We also find evidence for an additional resonance, namely the u+2(I), positioned at about 10 eV above the neutral ground state in the Franck-Condon region, and dissociating into O-+O(3P). The measurements suggest that the autodetachment lifetimes of the u+2(I) and g+2(II) states may be longer than previously suggested. It is also observed that the effects of electron energy loss (EEL) in the solid prior to DEA, O- scattering in the solid after dissociation, and the charge-induced polarization energy of the solid, broaden the Ek distributions, shift them to lower anion energies, and result in additional structure in them. The effects of EEL on the desorption dynamics of O- are estimated from high-resolution electron-energy-loss spectra and excitation functions for losses in the vicinity of the Schumann-Runge continuum of the physisorbed O2 molecules. We find indications for an enhancement of the optically forbidden X g-3A u+3 transition, and observe that the gas-phase Rydberg bands, for energy losses above 7 eV, are not distinguishable in the condensed phase. © 1995 The American Physical Society.