POLARIZATION ANISOTROPY IN RESONANT X-RAY-EMISSION FROM MOLECULES

We investigate the polarization anisotropy of resonant x-ray emission using one-step, two-step, and classical formulations. It is shown, ana lytically and numerically, that these models in general give different polarization anisotropies. We compare also the results of the one- an d two-step models for the integrated unpolarized cross sections over t he same set of test molecules. These include two of the chlorofluorome thanes used originally to experimentally verify the polarization aniso tropy in resonant x-ray emission. The test molecules also represent sp ecies with core-level chemical shifts and species with symmetry-adapte d and quasidegenerate core levels. It is shown that only in the case o f energy-isolated and localized symmetry-non-adapted core levels do th e two-step model and the - in that case identical-classical model appl y, while in all other cases, the one-step model is required either for the polarization anisotropy or for the total cross section, or for bo th these quantities.