Electron impact ionization of the outer valence orbital 1t2 of CH4

Abstract

The electron impact single ionization of the outer valence orbital 1t 2 of methane is investigated theoretically within a Sturmian approach. Using an expansion on a basis set of Generalized Sturmian Functions, all with correct asymptotic behavior, the ionization scattering amplitude is extracted directly from the expansion coefficients without the need of calculating a transition matrix element. Triple differential cross sections are obtained for several coplanar asymmetric geometries, and are compared with two sets of relative experimental data (incident energy of 500 eV and 250 eV). An absolute scale comparison with other available theoretical models is also presented, and the binary-to-recoil ratio, experimental and theoretical, is analyzed as a function of the momentum transfer. Like other theoretical results, ours reproduce only partially the experimentally observed cross sections features. Important differences in the position and height of the recoil peak, in particular, clearly indicate an agreement breakdown between the measurements and the presently available theories including ours. Finally, for an incident energy of 250 eV, ejected energy of 30 eV and a scattering angle of − 20°, we predict a double peak structure in the cross section binary region, which is a clear signature of the p-nature of the molecular orbital.