Forbidden Raman scattering processes. I. General considerations and E1--M1 scattering

The generalized theory of forbidden Raman scattering processes is developed in terms of the multipole expansion of the electromagnetic interaction Hamiltonian. Using the general expressions, the theory of electric dipole--magnetic dipole (E1--M1) Raman scattering is derived in detail. The 1S0→3P1 E1--M1 Raman scattering cross section in atomic magnesium is calculated for two applicable laser wavelengths using published f-value data. Since resonantly enhanced cross sections larger than 10-29 cm2/sr are predicted it should be possible to experimentally observe this scattering phenomenon. In addition, by measuring the frequency dependence of the cross section near resonance, it may be possible to directly determine the relative magnitudes of the Axp and AxA contributions to the scattering cross section. Finally, possible applications of the effect in atomic and molecular physics are discussed