Dramatic Effects of Relaxation on Many-Body Interactions: Atomic Photoionization of Outer Shells in the Vicinity of Inner-Shell Thresholds

Recent theoretical studies have indicated that cross sections for outer-shells in the vicinity of inner-shell thresholds exhibit significant structure, and this structure is j-dependent in spin-orbit doublets [1,2]. We report here on our measurements of the Xe 4d branching ratios in the vicinity of the 3d thresholds which showed structure but did not agree, even qualitatively, with theoretical predictions based on the relativistic-random-phase approximation (RRPA) [3]. It was found that adding relaxation to the calculation, RRPA with relaxation (RRPA-R) [4] brings theory and experiment into excellent agreement in the vicinity of the 3d thresholds. Since the 4d photoionization process in that region is dominated by many-body interactions in the form of interchannel coupling (configuration interaction in the continuum), this suggests that the inclusion of relaxation affects the interchannel coupling matrix element in this region. [1] R. Püttner, et al, J. Phys. B 54, 085001 (2021). [2] C. R Munasinghe, et al, Phys. Rev. A 106, 013102 (2022). [3] W. R. Johnson and C. D. Lin, Phys. Rev. A 20, 964 (1979). [4] V. Radojević, M. Kutzner and H. P. Kelly, Phys. Rev. A 40, 727 (1989).