Correlated radiative capture of two electrons with formation of heliumlike ion in the 1s2s 1S state

We investigate the correlated double-electron capture by a bare nucleus followed by the emission of a single photon and the formation of heliumlike ion in the excited 21S state. The total cross section of the process is calculated taking into account the leading orders of QED perturbation theory. The present evaluation is focused on the domain of collision energies, which allows for the dipole approximation in treatment of the electron-photon interaction. The universal scaling is found for the ratio of cross sections for capture into the 21S and 11S states. In the low-energy regime, the probability for the population of excited states is shown to exceed significantly that of the ground state.