Photoionization Branching Ratios of Spin-Orbit Doublets Far Above Thresholds

At higher energies far above thresholds where the spin-orbit splitting is comparably insignificant, branching ratios of the photoionization cross sections of spin-orbit (nl) doublets must go to the statistical value of (l+1)/l in the absence of relativistic effects. Therefore, the alteration of branching ratio from its statistical value at higher energies is indicative of relativistic interactions on the radial wave functions as predicted earlier [1] and verified experimentally recently [2]. To understand this relativistic behavior quantitatively, calculations were performed on noble gases using the relativistic-random-phase approximation (RRPA) based on the Dirac equation, which includes relativistic interactions in an ab initio manner along with many-body correlations. The results show that branching ratios well above the threshold are energy-dependent and move further away from the nonrelativistic values with increasing energy. This deviation increases with the increase of atomic number, which enhances the relativistic effects.   In addition, significant energy variations of the ratios are found, over broad energy ranges, owing to interchannel coupling with inner-shell photoionization channels,  as suggested by earlier studies [3,4]. [1] A. Ron, Y. S. Kim, R. H. Pratt, Phys. Rev. A 24, 1260 (1981); [2] R. Püttner, et al, J. Phys. B (in press). [3] E. W. B. Dias, et al, Phys. Rev. Lett. 78, 4553 (1997); [4] W. Drube, et al, J. Phys. B 46, 245006 (2013).