Resonance electron scattering from adsorbed molecules: Angular distribution of inelastically scattered electrons and application to physisorbedO2on graphite

We present a theoretical study of the angular distribution of electrons inelastically scattered after the vibrational excitation of molecules adsorbed upon crystalline surfaces through the formation of temporary negative ions. We develop a theoretical framework by which these angular emission profiles may be calculated and interpret measured angular distributions from a negative-ion resonance near 9 eV in physisorbed ${\mathrm{O}}_2$ on graphite. Using this method, we determine both the resonance symmetry and the orientation of the ${\mathrm{O}}_2$-molecular axis within the overlayer. The theory employs a proper treatment of the multiple scattering of the incident and emitted electrons within the surface which we show to be important in the energy range within which resonances are commonly observed.