Resonant X-ray Raman scattering from dense gases and solutions

To complement conventional theory of resonant X-ray Raman scattering (RXS) adapted either for rarefied gases or solids, we propose a theory and corres ponding analysis for RXS from dense gases and solutions. We show that the d ephasing broadening of the spectral lines due to interaction with buffer or solvent particles qualitatively changes the physics of the X-ray scatterin g. The dephasing results in an additional, two-step (TS) scattering, contri bution to the RXS cross-section, which interferes with the Raman one-step ( OS) channel and which shows a nondispersive behaviour, This results in a do ubling of the spectral lines by detuning the excitation frequency away from resonance. The theory is demonstrated numerically for RXS of formaldehyde in solution. (C) 2001 Elsevier Science BN. All rights reserved.