Low Even Configurations in the First Spectrum of Ruthenium (Ru I), part 2

A published calculation for the 4d(8), 4d (7)5s, and 4d(6) 5s(2) configurations of Ru I (R. E. Trees, J. Opt. Soc. Am. 49, 838 (1959).) is repeated in steps. Displacements produced by configuration interaction are evaluated, and departures of term positions from familiar expectations in the absence of configuration interaction are explained. The weaker perturbations produced by second-order effects of the spin-orbit interaction are then determined. It is shown that the neglect of these effects in published hand computations has obscured the remarkably good agreement between theory and observation that is obtainable in spectra of the second long period. The eigenvectors are based on “third-order eigenfunctions” which describe the levels simply, and show the degree of LS-coupling in a more quantitative manner.