Rotational excitation of physisorbedH2by low-energy electron scattering

The inelastic-scattering spectrum for pure rotational transitions $(J, m)=(0, 0)\to (2, m)$ by low-energy electrons ($2<E<\mathrm{}5\mathrm{}$ eV) is calculated for ${\mathrm{H}}_2$ molecules physisorbed on a flat surface. The anisotropic interaction with the surface is modeled by a ${cos}^2\theta$ potential, and scattering is assumed to be dominated by the ${}_{}{}^2{}_{}{}^{}\Sigma _u^{+}{}_{}{}^{}$ resonance. Comparison is made to the recent experimental results of Avouris, Schmeisser, and Demuth for ${\mathrm{H}}_2$ on Ag.