Nonadiabatic Atomic Distortion in Low-Energy Electron and Positron Scattering

A perturbation method is used to obtain equations for the dynamic distortion of the target atom in low-energy electron and positron scattering. In an approximation which is adequately simple for application to heavier systems, the equations for hydrogen are reduced to a form analogous to the perturbation equations of the method of polarized orbitals. After expressing the interaction of the incident particle with an atomic electron in terms of a multipole expansion, the equations are solved for the multipole components of the polarization potential, where the equations governing the distortion are dependent on the energy of the incident particle. Phase-shift results for electron and positron scattering on hydrogen are compared with adiabatic results and with results obtained by other nonadiabatic and variational methods.