The isotope dependence of the equilibrium rotational constants in 1Σ states of diatomic molecules

Abstract

From spectroscopic observations it is possible to deduce an adiabatic bond length for each isotope of a diatomic molecule. It is shown that the adiabatic bond lengths of the different isotopes depend linearly on the reciprocals of the masses of the two atoms, with coefficients that are in general distinct. Most previous treatments have assumed that the coefficients are equal. A similar mass-dependence applies to the bond lengths derived directly from the values of Y 01 (≈ B e ). This behavior can be used to deduce the equilibrium bond length of the molecule in the Born-Oppenheimer approximation. Applications to the precise experimental data for CO, HCl, and LiCl are described, but only in the case of CO is there a definite indication that the two coefficients in the adiabatic bond length are required experimentally.