SPECTRAL FEATURES OF RESONANT RADIATIVE X-RAY RAMAN-SCATTERING BY POLYMERS AND SOLIDS

A theory of radiative resonant x-ray Raman scattering by polymers and solids is presented. A detailed analysis demonstrates the crucial role of the momentum exchange between valence electrons and photons and be tween valence electrons and the core hole. It is shown that resonant i nelastic x-ray scattering (RIXS) cross sections of pi-electron systems is equal to zero in the frozen-orbital approximation. The photon mome nta open the RIXS channels near the Fermi level, while the electron-co re-hole interaction makes RIXS transitions allowed from all occupied s tates. A strong influence of the soft x-ray photon diffractional scatt ering on the RIXS spectral shape is predicted, with the wavelength pla ying the role of a coherence length of interaction with the electromag netic field. Due to the excitonic character of photoabsorption transit ions near threshold, a resonant structure appears in the RMS profile a bove thr Fermi level. A strong dependence of the dispersion above the photoabsorption threshold on the strength of the excitonic peak is pre dicted, with the RIXS band split into two qualitatively different side bands. The position of the first, main, band is practically independen t on the excitation energy for weak excitonic states. The position of the second band, caused by tail excitation of excitonic states, follow s the Raman-Stokes dispersion law.