Isotopic dependence of Born-Oppenheimer breakdown effects in diatomic hydrides: The B1Σ+ and X1Σ+ states of HF and DF

A numerical procedure for reducing spectroscopic line positions to isotopically self-consistent radial Hamiltonian operators is applied to the X1Σ+ and B1Σ+ electronic states of the diatomic isotopomers HF and DF. The rotational assignments for DF (B → X) are significantly extended and now include information on v″ = 9–26 of X1Σ+ and v′ = 0–7 of B1Σ+. A least-squares fit of 5213 spectral line positions has resulted in precise internuclear potential functions for both isotopomers and a single purely nonadiabatic function q(R) which simultaneously describes rotational energy level shifts in the ground states of both isotopomers, in accord with theoretically expected behavior. Model calculations are carried out to critically test the reliability of the procedure. An improved estimate of the electronic isotope shift of B1Σ+ is obtained as ΔTe = TeB(HF) - TeB(DF) = −2.48(7) cm−1. Predissociation observations in X1Σ+ are explained quantitatively through the calculation of half-widths Γfwhm from the fitted operators. For HF, the calculated widths agree very well with experimental estimates obtained from appreciably broadened spectroscopic lines. Quantum-mechanical molecular constants are calculated for the lower vibrational levels of TF (X1Σ+).