Calculation of the 1s-2s Electron Excitation Cross Section of Hydrogen

The zero order partial cross section for the excitation of hydrogen from the (1s) to the (2s) states by electron collision has been calculated by a numerical method. Full allowance has been made for electron exchange and all direct coupling between the initial and final atomic states has been retained. The cross sections obtained are compared with those that have been calculated by more approximate methods. In particular, the cross section near the threshold is found to be considerably smaller than that given by Erskine and Massey using the distorted wave approximation.