Full Second-Order Distorted-Wave Calculation without Approximations for Atomic Excitation by Electron Impact

A new technique has been developed for evaluating second-order distorted-wave amplitudes for atomic excitation without making any approximations. By this technique, second-order amplitudes with arbitrary distorted waves and arbitrary Green's functions in the interaction can be evaluated with comparable difficulty. The utility of the method is demonstrated through a practical calculation of the second-order distorted-wave approximation for electron excitation of the $2p$ state of hydrogen.