T-matrix calculations for the electron-impact ionization of hydrogen in the Temkin-Poet model

An eigenchannel R-matrix expansion of the T matrix is used to calculate total integrated and ejected energy differential cross sections for the electron-impact ionization of hydrogen in the Temkin-Poet model. In previous close-coupling results, unphysical oscillations in the total ionization cross section could be averaged over due to the smooth dependence of the cross section on the incident energy. For differential ionization cross sections, a step-function behavior in the cross sections’ overall ejected energy dependence has made unphysical oscillation removal much more problematic. By formulation design, the T-matrix method eliminates the stepfunction problem found in most close-coupling calculations of the ejected energy differential cross section. Total and differential ionization cross sections in a one-state R-matrix expansion are in excellent agreement with Hartree-Fock distorted-wave results. Total and differential ionization cross sections in multiple state R-matrix expansions converge toward the more accurate results given by a time-dependent wave-packet method. Unphysical oscillations appear in the differential ionization cross sections for all the T-matrix results involving more than three states in the R-matrix expansion, but the oscillations are small, symmetric about E/2, and easily averaged to give a smooth uniform result.