Simulations of resonant X-ray emission spectra of molecules

We illustrate the informational content and different aspects of resonant elastic and inelastic X-ray emission spectroscopy of free molecules by reviewing results from recent ab initio calculations. We let each molecule, or group of molecules, represent one particular aspect: calculations on molecular oxygen, benzene, carbon dioxide, aniline, fullerenes, 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 character of band gap excited spectra, polarization anisotropies, the role of screening, and the role of excitons.