The results of three different methods of calculation are compared, with extrapolation and fitting of observational data, to obtain values for the energy levels and intervals of the 2sr 2pk configurations for the elements from sulfur to scandium. Some auxiliary results are also obtained, such as fine-structure parameters which account well for the observed splittings, and intercombination-line wavelengths of interest for the solar corona.
S. O. Kastner, "Energy levels of 1s22sr2pk configurations in the C I and N I sequences, in S, Cl, Ar, K, Ca," J. Opt. Soc. Am. 63, 738-744 (1973)