Behaviour of the asymptotic cross section for excitation of hydrogen atoms by electron impact

The asymptotic (with respect to n) cross section for the excitation of hydrogen atoms by electron impact has been studied in the energy range 20 eV to 1 keV. The effect of electron exchange has also been incorporated using various first-order approximations. The cross section for excitation into different angular momentum states are found to obey a scaling law. Results are presented for 900 polarisation Lyman α radiation together with the alignment parameter. The ratio of the angular distributions for αs and αp states are also discussed. (author)