Polarizability interaction in molecules and double-well tunneling

Directional superpositions of the rotational states of linear molecules can:be created by interaction of the polarizability with the strong electric field of an intense laser beam. The polarizability interaction, proportional to cos(2) theta (with theta the angle between the molecular axis and the direction of the electric field), is a double-well potential, with end-for-end symmetry. The energy levels thus exhibit tunnel-effect splittings. We present an exact treatment, derived by transcription to an oblate spheroidal wave equation. We also develop an accurate semiclassical approximation, in which the action integral and period are evaluated using an effective potential that corresponds to one-dimensional motion. The results pertain both to rotational spectroscopy of nonpolar molecules and to alignment and trapping experiments with either nonpolar or polar molecules.