Author ORCID Identifier


Date of Award


Degree Type


Degree Name

Doctor of Philosophy (PhD)


Physics and Astronomy

First Advisor

Steven T. Manson

Second Advisor

Vadym Apalkov

Third Advisor

Russel White

Fourth Advisor

Mukesh Dhamala


Photoionization studies of atomic subshells have long been important tools in understanding the properties of atomic, molecular, and condensed matter systems. Recently, the ratio of photoionization cross section of atomic subshells split by the spin-orbit interaction (branching ratio) is gaining more attention in the scientific community because of the achievement of experimental measurements, which were impossible a few years ago. In this theoretical study to investigate the relativistic behavior of the photoionization process and to identify the interchannel coupling effects, numerical calculations were performed on noble gases (Ne, Ar, Kr, Xe, and Rn) and Hg using the relativistic-random-phase approximation (RRPA) based on the Dirac equation, which includes relativistic interactions in an ab initio manner; it also includes significant aspects of electron-electron correlation in initial and final state wave functions of the photoionization process.

At higher energies far away from the inner shell thresholds where the spin-orbit splitting is comparably insignificant, the branching ratio of spin-orbit (nl) doublets must go to the statistical value (l+1)/l in the absence of relativistic effects. We found the alteration of branching ratios from its statistical value at higher energies which indicates the relativistic interaction on the radial wave functions. Also, it has been found that the mechanism of interchannel coupling of the final state wave functions significantly influences the branching ratios of outer-shell doublets in the vicinity of inner-shell thresholds. Furthermore, it was found spin-orbit interaction activated interchannel coupling effects in Hg 3d, Rn 3d, and Rn 4d spin-orbit doublets.

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