The effect of an external magnetic field on the determination of E1M1 two-photon decay rates in Be-like ions

In this work we report on ab initio theoretical results for the magnetic-field-induced 2s 2p 3P0 → 2s2 1S0 E1transition for ions in the beryllium isoelectronic sequence between Z = 5 and 92. It has been proposed that therate of the E1M1 two-photon transition 2s 2p 3P0 → 2s2 1S0 can be extracted from the lifetime of the 3P0 state inBe-like ions with zero nuclear spin by employing resonant recombination in a storage ring. This experimentalapproach involves a perturbing external magnetic field. The effect of this field needs to be evaluated in orderto properly extract the two-photon rate from the measured decay curves. The magnetic-field-induced transitionrates are carefully evaluated, and it is shown that, with a typical storage-ring field strength, it is dominant or of thesame order as the E1M1 rate for low- and mid-Z ions. Results for several field strengths and ions are presented,and we also give a simple Z-dependent formula for the rate. We estimate the uncertainties of our model to bewithin 5% for low- and mid-Z ions and slightly larger for more highly charged ions. Furthermore we evaluatethe importance of including both perturber states, 3P1 and 1P1, and it is