Theoretical spectroscopy of the NO radical. II. Λ doubling in the ground X 2Π state and spin–orbit effects in the excited Π states

Abstract

Spin–orbit splittings of the a 4 Π and the 2Π states X, C, B, and L of the NO radical were calculated as a function of internuclear separation R using multireference configuration interaction wave functions and the potential curves presented in part I of this work. The resulting values averaged over vibrational levels, agree within a few wave numbers with the experimental data whenever available. Subsequently the R-dependent Λ splitting of the X2Π ground state is determined in a perturbation matrix procedure which is independent of Hund’s coupling cases taking into account 2Σ+, 2Σ−, 4Σ−, 4Σ+, 4Π and 2Δ states as possible perturbers. The resulting splitting (0.011 81 cm−1) of the first vibrational level of the 2Π1/2 component compares well with the experimental value of 0.011 88 cm−1. The analysis of the contributions of the various perturbers to the Λ splitting shows that the 2Σ+ states and the G2 Σ− state are dominant and determine the magnitude of the splitting. A possible change of the parity with R is indicated which also affects the magnitude of the splitting.