Elastic scattering and excitation of the 1s to 2s and 1s2p transitions in atomic hydrogen by electrons to medium to high energies

Multi-pseudostate close coupling is used to investigate 1s to 1s, 1s to 2s and 1s to 2p scattering at energies from 54.4 to 350 eV. Two sets of pseudostates are considered. The first is that of Fon et al. (1981); the second is an improved set. In constructing the improved pseudostates emphasis is placed upon getting the second Born term right. Target states of angular symmetries not included in the pseudostate bases are taken into account by using the distorted-wave second Born approximation of Kingston and Walters (1980). Results for elastic scattering are satisfactory; it is estimated that the present elastic differential cross sections are accurate to better than 5% at any angle at 200 and 300 eV. For the 2s and 2p excitations the theoretical picture is not so clear. Here there are significant differences between our results and the experiments of Williams (1975) and of Williams and Willis (1975). Some other theoretical calculations are in better accord with these experiments, although the authors believe the present work to be on firmer ground. Cases where the theoretical approximations are unanimously in disagreement with experiment suggest the presence of inaccuracies in the measurements and highlight the need for further experimental investigation. Of special interest are the angular correlation parameters of the 1s to 2p excitation; their results are in reasonable agreement with the main experiment at 54.4 eV in the angular range up to 70 degrees ; beyond 70 degrees there are still problems to be resolved.

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