Anisotropy of polarized x-ray emission from molecules

X-Ray Scattering and Fluorescence From Atoms and Molecules

“…82,83 Gel'mukhanov and Mazalov 84 predicted that excitation of molecules near threshold to states of specific symmetry will result in polarized x-ray fluorescence. This effect was observed by Lindle et al 48 in Cl K-V resonant x-ray fluorescence from C H 3 Cl and was followed by several experimental studies in which the x-ray spectrometer of Fig. 14 was rotated to measure either the polarization 48-50,52-54 or angular distribution 51,55,56 of emitted x-rays.…”

“…41 In particular, several polarizationdependent studies have been made on Cl-containing molecules of Cl K-V x-ray emission, in which a valence electron fills a vacancy in the Cl K-shell. [48][49][50][51][52] For incident x-ray energies near the Cl K-edge (ª2820-2880 eV) and for the Cl K-V x-ray fluorescence (ª2800-2820 eV), the Bragg angles for Si(111) crystals are ª43°-45°, giving essentially complete polarization selectivity. Polarization-selective measurements have also been made on Scontaining molecules 53,54 and on atomic Ar.…”

“…14 can be rotated about the emitted x-ray direction to measure the fluorescence polarization, 48 or it can be rotated about the incident x-ray beam direction to measure the angular distribution of polarized fluorescence. 51 Such measurements give information on the spatial alignment of resonantly-excited molecules and on the symmetries of the electronic states (Section 8).…”

“…Electronic states and transition moments must reflect the symmetry properties of molecular geometries, which provides the basis for producing aligned molecules by resonant x-ray absorption and symmetry-dependent polarization anisotropies in x-ray emission. A simple, classical two-step model 87,88 has been used to qualitatively understand molecular x-ray polarization anisotropies 51 and will be discussed here. However, resonant x-ray emission should be described as a onestep, resonant inelastic scattering process, i.e., as XRRS but with uniquely molecular features.…”

Studies of Solids and Adsorbates in Synchrotron Radiation Excited Soft X-Ray Fluorescence

“…For other spectroscopic methods like photoemission and X-ray absorption the well-defined polarization of synchrotron radiation has been extensively used, and it has also been introduced as an important element in X-ray emission spectroscopy [4].…”