Level-crossing spectroscopy with an electric field: Stark shift of the 3P2 term in lithium

The method of level-crossing spectroscopy has been extended to a study of the Stark effect on the 3P term of lithium. Lithium atoms in a broad atomic beam are subjected to collinear electric and magnetic fields. The field values required to produce a level crossing or degeneracy are determined by observing the change in the angular distribution of the fluorescence resulting from the optical excitation of the 3P term. The magnetic field required to produce the crossing is found to shift to higher values as the electric field is applied. The shift increases as the square of the electric field and is given by ΔH=+0.056(11)E2, where ΔH is in gauss and E is in kilovolts per centimeter. The coefficient is in good agreement with the value 0.048 obtained from second-order perturbation theory and the Bates and Damgaard approximation.