Two-photon transitions in atomic inner shells: Relativistic and atomic-screening effects.

We present a relativistic self-consistent-field calculation of two-photon decay rates in atomic inner shells. By comparing our relativistic two-photon decay rates for Mo, Ag, and Xe with results for a series of hydrogenlike ions and existing nonrelativistic results, we identify and clarify the nature of the relativistic effects and atomic screening effects: (1) the relativistic effects reduce the two-photon decay rates compared with the nonrelativistic results; (2) screening reduces the atomic two-photon decay rates compared with the corresponding H-like ions. We also compare our results with recent experiments and with other theoretical calculations. Our results are in reasonable agreement with the experimental measurements, except for the 2{ital s}-1{ital s} transitions, and with other theoretical calculations, except for the {ital nd}-1{ital s} results of Mu and Crasemann (Phys. Rev. Lett. 57, 3039 (1986); Phys. Rev. A 38, 4585 (1988)).