Two-channel relativistic random-phase approximation applied to the photoionisation of helium- and beryllium-like ions

Abstract

Atomic photoionisation cross sections including both relativistic and correlation effects for the helium and beryllium isoelectronic sequences are calculated in two-channel relativistic random-phase approximation (RRPA). By studying the relativistic E1 transition along the sequence, the coupling between the low-energy photoelectron and the core electron (electrons) is found to deviate from relativistic jj coupling even for high Z elements. The deviation of the sum of dipole oscillator strength from the non-relativistic Thomas-Reiche-Kuhn rule is also investigated.