Impact-Parameter Treatment of Hydrogen-Hydrogen Excitation Collisions. I. Two-State Approximation

The impact-parameter versions of the full two-state and the Born approximations are used to calculate the n=2 and 3 single-excitation cross sections describing collisions between two ground-state hydrogen atoms. Effects similar to those encountered by Bates in his distortion calculations of the $2s$ and $2p$ excitations of hydrogen by proton impact are observed. Cross sections for excitation up to the $4s$ state are also provided by using the Born approximation. The percentage polarization of impact radiation emitted is evaluated.