Journal of Chemical Physics, Vol.100, No.5, 3940-3956, 1994
Substrate Dependence of Electron-Stimulated O- Yields from Dissociative Electron-Attachment to Physisorbed O-2
We present measurements of O- electron stimulated desorption yields obtained under identical experimental conditions from 0.15 monolayers (ML) of O-2 deposited onto disordered substrates consisting of 4 ML of either Kr, Xe, C2H6, C2H4, N2O, CH3Cl, or H2O, all condensed on Pt (polycrystalline). The resulting O- yield functions, for incident electron energies below 20 eV, are compared to that obtained from the O-2/Kr solid; this allows us to assess the order of magnitude effects of the local substrate environment on dissociative electron attachment (DEA) via the (2) Pi(u), and gas phase forbidden (2) Sigma(g,u)(+) resonances of O-2(-). We note that, in addition to electron energy losses in the substrate prior to DEA to O-2 and past-dissociation interactions of the O- with the substrate molecules, charge or energy transfer from the O-2(-) transient anion to a substrate molecule, and capture of the incident electron into a dissociative anion resonance of the substrate molecule may contribute to a reduced O- yield from the physisorbed O-2. In the case of O-2 deposited on amorphous ice, we find that the O- signal from DEA to O-2 is completely absent for electron energies below 14 eV; we attribute this to a complete quenching of the dissociative O-2(-)((2) Pi(u), (2) Sigma(+)) resonances by the adjacent water molecules.
Keywords:LOW-ENERGY ELECTRONS;CORE-EXCITED RESONANCES;TOTAL CROSS-SECTIONS;VIBRATIONAL-EXCITATION;TRANSMISSION SPECTRA;SURFACE-REACTIONS;CONDENSED O-2;AR-FILMS;MOLECULAR POLARIZABILITY;SHAPE RESONANCES