Finite nuclear mass corrections to electric and magnetic interactions in diatomic molecules

In order to interpret precise measurements of molecular properties, finite nuclear mass corrections to the Born-Oppenheimer approximation have to be accounted for. It is demonstrated that they can be obtained systematically using nonadiabatic perturbation theory. The formulas for the leading corrections to the relativistic contribution to energy, the transition electric dipole moment, the electric polarizability, and the magnetic shielding constant are derived. They can be conveniently calculated for a fixed position of nuclei, as in the Born-Oppenheimer approximation, and then averaged over the rovibrational function.