By means of a quantitative analytic treatment, we have calculated the adiabatic and nonadiabatic effects on the vibration-rotational energies of diatomic molecules. We have proved that one can in principle determine independently one coefficient of each radial function representing the rotational nonadiabatic and adiabatic effects whereas because the remaining coefficients of the three radial functions representing the adiabatic, rotational and vibrational nonadiabatic effects appear in inextricable linear combinations they cannot be individually determined from experimental measurements of transition frequencies in the absence of external-electric and magnetic fields.