SIMULATIONS OF RESONANT X-RAY-EMISSION SPECTRA OF MOLECULES

We illustrate the informational content and different aspects of reson ant elastic and inelastic X-ray emission spectroscopy of free molecule s by reviewing results from recent ab initio calculations. We let each molecule, or group of molecules, represent one particular aspect: cal culations on molecular oxygen, benzene, carbon dioxide, aniline, fulle renes, chlorofluoromethanes, carbon monoxide, and polyenes are used to illustrate, in order, the effects of parity selection rules and core hole localization, vibronic coupling and symmetry breaking, frequency dependence of symmetry breaking, the role of chemical shifts, the char acter of band gap excited spectra, polarization anisotropies, the role of screening, and the role of excitons.