Kinetic-energy distributions of O[sup [minus]] produced by dissociative electron attachment to physisorbed O[sub 2]

We report measurements of the kinetic energy ([ital E][sub [ital k]]) distributions of O[sup [minus]] produced by low-energy electron impact (5.5--19.5 eV) on disordered multilayers of O[sub 2] physisorbed on a polycrystalline Pt substrate. The results confirm that dissociative electron attachment (DEA) proceeds via the formation of the [sup 2][Pi][sub [ital u]], [sup 2][Sigma][sub [ital g]][sup +](I), and [sup 2][Sigma][sub [ital x]][sup +](II) ([ital x]=[ital g] and/or [ital u]) states of O[sub 2][sup [minus]*]. We also find evidence for an additional resonance, namely the [sup 2][Sigma][sub [ital u]][sup +](I), positioned at about 10 eV above the neutral ground state in the Franck-Condon region, and dissociating into O[sup [minus]]+O([sup 3][ital P]). The measurements suggest that the autodetachment lifetimes of the [sup 2][Sigma][sub [ital u]][sup +](I) and [sup 2][Sigma][sub [ital g]][sup +](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[sup [minus]] scattering in the solid after dissociation, and the charge-induced polarization energy of the solid, broaden the [ital E][sub [ital k]] distributions, shift them to lower anion energies, and result in additional structure in them. The effects of EEL on the desorption dynamics ofmore » O[sup [minus]] 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 O[sub 2] molecules. We find indications for an enhancement of the optically forbidden [ital X] [sup 3][Sigma][sub g][sup [minus]][r arrow]A [sup 3][Sigma][sub u][sup +] transition, and observe that the gas-phase Rydberg bands, for energy losses above 7 eV, are not distinguishable in the condensed phase.« less