Fine structure of the Formula Presented energy levels of singly ionized carbon (C ii)

Benchmark variational calculations of the lowest eight Rydberg Formula Presented states of the singly ionized carbon atom (stable isotopes Formula Presented, and Formula Presented, as well as the infinite nuclear mass ion Formula Presented) are reported and the fine structure of the energy levels is determined. The nonrelativistic wave functions of this six-particle, five-electron system are approximated using an expansion in terms of up to 16 000 all-particle explicitly correlated Gaussians, the nonlinear variational parameters of which are extensively optimized using a procedure that employs the analytic energy gradient. These highly accurate wave functions are used to compute the fine-structure splittings including the corrections due to the electron magnetic moment anomaly. The results obtained in this paper are considerably more accurate than the data from the previous theoretical calculations and from the available experimental measurements. The present data can be useful in guiding future accurate spectroscopic measurements of C ii.