Photodissociation of molecules oriented by dc electric fields: Determining photofragment angular distributions

Abstract

A quantum mechanical model has been derived for the photofragmentation of a molecule that is preoriented by a moderate to large dc electric field. The hybridization of the rotational wave functions in the dc electric field gives rise to net orientation and the resulting state mixing breaks the symmetry that is normally responsible for the fact that many laboratory measurements are only sensitive to a single anisotropy parameter (β). Consequently, the laboratory photofragment angular distributions resulting from molecules dissociated from ‘‘pendular’’ type states are sensitive to all of the terms in the Legendre expansion of the center-of-mass angular distribution, up to a value determined by the magnitude of the electric field. In essence, the electric field ‘‘locks’’ the molecule fixed frame onto the space fixed frame determined by the field direction. Additional advantages of this approach include the fact that the anisotropy is not quenched by rotation or hyperfine depolarization, owing to the fact that the orientation of the molecule is controlled by the electric field. The application of this method to angularly resolved photofragment experiments and Doppler spectroscopy is discussed.