A b i n i t i o calculation of higher order corrections to Λ doubling and spin splitting in diatomic molecules

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Abstract
Higher order corrections to the L doubling in 2R states and spin splitting in 2S states of diatomic molecules have been derived by use of a Van Vleck transformation to third order. The corrections are expressed in terms of the parameters pJ, qJ, and gN, normally introduced through the phenomenological replacements pv→pv+pJJ(J+1), qv→qv+qJJ(J+1), and gv→gv+gNN(N+1). The molecules investigated are OH, OD, and SH, and ab initio values for pJ, qJ, and gN are computed for the X 2R,v = 0 and A 2S+,v = 0 states. The electronic matrix elements were obtained within the Hartree–Fock approximation, and vibrational eigenfunctions were computed from Morse curves for OH and OD and from RKR potentials for SH. Comparison of ab initio values and experimentally derived parameters shows reasonable agreement.