Coulomb-Born calculation of the triple-differential cross section for inner-shell electron-impact ionization of carbon

A Coulomb-Born approximation is used to compute the triple-differential cross section for electron-impact inner-shell (1s) ionization of carbon. We employ a perturbation series that allows the use of Coulomb waves with arbitrary ${\mathit{Z}}_{\mathrm{eff}}$ for the incoming, scattered, and ejected electrons. Most of the features of the triple-differential cross section observed experimentally are reproduced, even though these wave functions are distorted by an effective Coulomb potential and therefore do not satisfy the plane-wave boundary conditions at infinity. In order to explain some features that appear in the cross section, and in order to probe the validity of a dipole approximation, we make a multipole expansion of the transition matrix and show that the amplitudes of the multipole components are similar to those obtained in the Born approximation, while the relative phases of the multipoles differ greatly.