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This dissertation comprises four investigations concerning the photoionization of open-shell atoms. The first two are concerned with anisotropic interaction effects on the photoelectron angular distribution of open-shell atoms within the Hartree-Fock approximation. Calculations are carried out for the outer p-subshells of the halogen (F, Cl, Br, and I) and chalcogen (O, S, Se, and Te) atoms as well as for the 3s-subshell of atomic Al. Large anisotropic interaction (i.e., LS-term-dependent) effects are found for the photoelectron asymmetry parameter (beta) in all cases except for the light elements F and O. Comparison is made to central potential model calculations. The second two investigations are concerned with the development and application of a many-body treatment of open-shell atom photoionization processes using a transition matrix approach. The aim of this investigation is to treat all particle-hole-type interactions so that theoretical photoionization cross sections for open-shell atoms can be calculated with the same accuracy as are random-phase approximation (RPA) results for closed-shell atoms. A graphical procedure is developed to evaluate each term in the equation satisfied by the first-order transition matrix. For those terms involving the interaction of excited virtual pairs of electrons with the ionic core, the interaction is approximated by allowing no exchange of orbital or spin angular momentum with the ionic core. This approximation leads to the RPA in the closed-shell atom case; it is used to define the RPA here for open-shell atoms. This new open-shell transition matrix approach is applied to the calculation of the photoionization cross section of atomic chlorine. Comparison is made to the results of other theoretical approaches.

A graphical procedure is presented for evaluating each term in the equation satisfied by the first-order transition matrix for an arbitrary (open-shell) atom. For those terms involving the interaction of excited virtual pairs of electrons with the ionic core, we introduce the approximation that there is no exchange of orbital or spin angular momentum with the ionic core. This approximation is shown to lead to the random-phase approximation (RPA) equations in the closed-shell-atom case; we use it to define the RPA for open-shell atoms. The single equation satisfied by the first-order transition matrix is used to obtain a set of N+N′ coupled differential equations for N final-state radial functions and N initial-state radial functions, which together, completely determine the first-order transition matrix for an atomic system having N final-state channels. (The relation of N′ to N depends on the particular atom studied). The N+N′ differential equations are shown to reduce to familiar forms in the following cases: (1) When initial-state correlations are ignored, one obtains the close-coupling equations and (2) when closed-shell atoms are considered, N=N′ and one obtains the 2N coupled differential equations of the Chang-Fano version of the RPA. Finally, our RPA first-order transition matrix is used to evaluate the matrix element of the electric-dipole operator for an arbitrary (open-shell) atom. These RPA electric-dipole transition matrix elements may be used to calculate nonrelativistically all experimentally observable quantities resulting from a single-electron atomic photoabsorption process.

The authors present a survey of the photoionization cross sections and photoelectron angular distributions for the outer p subshell of the chalcogen atoms O, S, Se, and Te and the halogen atoms F, Cl, Br, and I. Results are presented in the Hartree-Fock approximation as well as in the central-potential-model approximation. An extensive analysis and comparison of the results obtained is presented which finds that exchange-interaction effects are strongest for the n=3 row elements.

Photoelectron angular distribution asymmetry parameters for photoionization to each of the three term levels of the Cl+ ion are calculated above the 1S ionic threshold with use of the open-shell transition-matrix method. Comparison is made with frozen-core Hartree-Fock asymmetry parameters and with the multiconfiguration Hartree-Fock results of Fielder and Armstrong. The calculated asymmetry parameters are used to estimate partial-cross-section branching ratios at 584 Å from the relative experimental photoelec- tron intensity measurements of Kimura, Yamazaki, and Achiba.