High-precision calculations of the 1s22s2p 1P1RT1s22s2 1S0 spin-allowed E1 transition in C III

Large-scale relativistic calculations are performed for the transition energy and line strength of the 1s22s2p1P1−1s22s21S0 transition in Be-like carbon. Based on the multiconfiguration Dirac-Hartree-Fock (MCDHF) approach, different correlation models are developed to account for all major electron-electron correlation contributions. These correlation models are tested with various sets of the initial and the final-state wave functions. The uncertainty of the predicted line strength due to missing correlation effects is estimated from the differences between the results obtained with those models. The finite nuclear mass effect is accurately calculated taking into account the energy, wave functions, as well as operator contributions. As a result, a reliable theoretical benchmark of the E1 line strength is provided to support high-precision lifetime measurement of the 1s22s2p1P1 state in Be-like carbon.