Date of Award

1983

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Abstract

The scattering of electrons by hydrogen atoms at intermediate energy range, where the problem is difficult due to electron atom correlations, is investigated. All possible processes of elastic scattering, excitation and ionization are considered. A simplified model is considered in which all terms involving non-zero angular momenta are neglected. Elastic scattering and excitation cross-sections for the 2s and 3s states are calculated for this model with the use of close-coupling expansion with four pseudostate bases of rather different character. Pseudothreshold structure is observed for ('1)S states and removed with a T-matrix fitting procedure. It is found that, after removal of this structure, the results agree quite well with each other and with the exact results for this model which were given previously by Poet. The same is true for the ('3)S state results which exhibit no pseudoresonances. The total cross-section (inclusive of all scattering) is calculated as a function of energy for the same model. In the ('1)S state, for which the short range correlation between the electrons is important, the two-body Schroedinger equation is integrated numerically, and the optical theorem is used to determine the total cross-section. The problem of numerical instability is substantially alleviated by using an explicity orthogonalized set of target wave-functions. The results agree rather well with those obtained from all four pseudostate bases sets. High and low bounds are given for the ionization cross-section, and these are compared with estimates of ionization obtained from a pseudostate expansion. The total cross-sections for the ('3)S state are calculated for the four bases sets using optical theorem with a remarkably good agreement amongst each other. At low energies, most of the scattering is found to occur in the elastic channel; the reason for which can be traced back to the Pauli exclusion principle. The differences, which are not large, in the ionization cross-sections with different basis sets indicate the extent of the completeness of the basis sets. Cross-sections for the ionization of hydrogen atoms by electron impact in the real problem have been computed using a projection technique. The resulting values are found to be underestimates.

Pages

123

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