where the ai are the anharmonic potential constants that can be evaluated from the higher Yij coefficients. The equilibrium internuclear distance is then expressed as:
Since Dunham's treatment utilizes the Born-Oppeniheimer approximation, the value of Be must be modified for breakdown of this approximation. Several methods have been developed for handling these corrections; the most important are those of Rosenblum et al. , Bunker , and Watson .