Post-Threshold Behavior of the Cross Sections for the 1s−2p Excitation by Electron Impact

Detailed numerical reexamination of the $1s\ensuremath{-}2p$ cross section for the excitation of hydrogen by electron impact shows structure at 10.4 and 10.6 eV which has not been previously reported. The calculations tend to confirm the recent data of Williams and McGowan. It is suggested that the structure is the result of interference between background potential scattering and the resonance just above $n=2$ threshold.