RESONANT ELECTRONIC EXCITATION OF O-2 ON GRAPHITE

A high-resolution electron-energy-loss spectroscopic study of O2 monolayers physisorbed on graphite (in the ζ2-phase) reveals a resonance in the cross section for the X3Σg-→a1Δg electronic excitation of O2 at an electron beam energy of 8 eV, and is attributed to the formation of a temporary negative ion. Measurements of the angular dependence of the inelastically scattered electrons, in conjunction with multiple electron-scattering calculations, show that the intermediate state has dπ symmetry, consistent with the 2Πg resonance observed in gas-phase electron-scattering studies. The angular distributions also provide evidence for dynamical molecular tilting of the molecular axis about its equilibrium position in both the ζ2- and δ-phases of O2 on graphite. © 1990.