Nondipole Resonant X-Ray Raman Spectroscopy: Polarized Inelastic Scattering at theKEdge of Cl2

X-Ray Scattering and Fluorescence From Atoms and Molecules

“…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.…”

“…The 1s u AE 5s u transition is dipole forbidden, but becomes significant in the Cl 2 case for which the x-ray wavelength is comparable to internuclear distance. 52 The x-ray emission spectrum recorded on the 5s u resonance with parallel polarization is plotted in the top of Fig. 25 , are also strongly populated.…”

“…We also assume that x-ray absorption and emission are well described as electric-dipole transitions, an approximation that was recently shown to break down in the case of resonant x-ray emission from Cl 2 . 52 The Cl 2 case will be discussed in the next section. Here we discuss experiments for which the electric-dipole approximation is expected to be valid.…”

“…52 Molecular Cl 2 , however, contains two equivalent Cl atoms separated by an internuclear distance ª2.0 Å, suggesting that the XRRS process will be sensitive to variations of the phase of the incident and emitted x-rays over the interatomic distance. 52,94 This idea was confirmed experimentally and explained theoretically in an XRRS study of Cl 2 that was recently reported by Mills et al 52 It was necessary to treat the full exponential factor of the photon-electron interaction in the Kramers-Heisenberg formula, which resulted in showing how the XRRS spectrum is sensitive to diffraction-like structure factors. 52 The discussion here will be limited to the experimental observation of nondipole final states in the polarized XRRS spectra of Cl 2 .…”

“…Predictions for XRRS spectra of Br 2 were also calculated by Mills et al 52 The previous section discussed how the symmetries of molecular electronic states and transition dipole moments are related to polarization anisotropies of XFS. Among the symmetry properties which characterize states of homonuclear diatomic molecules is inversion through the center of symmetry.…”