Perturbation for a rigid rotator in an electric field

The behavior of a rigid rotor perturbed by an electric field is studied. An hypervirial calculation, to obtain the perturbation series without calculation of the perturbed wavefunctions, is used to determine the Stark-shifted eigenvalues. A numerical estimation of the m equals; 0 → m = 1 transition for the lowest vibrational state (v = 0) and the first rotational state (J = 1) for the HF and DF molecules using Padé approximants is made.