The 1 s -2 s excitation of hydrogen atoms by electron impact

Abstract
The expression for the cross-section obtained from the second Born approximation by including only terms to the third order in the interaction energy is employed to calculate cross-sections for the electron impact excitation of the 2s level of atomic hydrogen, allowance being made for distortion and polarization due to the 1s, 2s and 2p$_{0,\pm1}$ intermediate states. These cross-sections are compared with the available experimental data.