MOLECULAR POLARIZED X-RAY RAMAN FLUORESCENCE SPECTROSCOPY

Author Institution: Indiana University, Bloomington, IN 47405.Cross sections differential in energy, angle, and polarization have been constructed from the general Kramers-Heisenberg relation for resonant (two-photon) scattering of polarized x-rays from a homogeneous, isotropic ensemble of diatomic or polyatomic molecules. Rotational selection rules consequent of the electronically inelastic nondiagonal polarizability tensor are clarified. Correct analytical treatment of resonant contributions to the cross section indicates the possibility of complex (Fano-like) lineshapes in the presence of strong mixing between intermediate core-electron hole states and the degenerate background of continuum Auger states largely responsible for their decay. The ranges of physical parameters giving rise to the various characteristic Fano shapes, fundamental differences resulting from discrete or continuum resonant excitation above or below core-electron thresholds, and contributions from nonresonant processes are described. Illustrative applications incorporate the effects of finite resolution in incident and detected photon energy on molecular spectra recently measured with synchrotron radiation. Circumstances in which the appropriately broadened rovibronic scattering cross sections are well-approximated by classical (angle-averaged) treatment of rotational degrees of freedom are indicated