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 between valence electrons and the core hole. It is shown that resonant inelastic x-ray scattering (RIXS) cross sections of π-electron systems is equal to zero in the frozen-orbital approximation. The photon momenta open the RIXS channels near the Fermi level, while the electron-core-hole interaction makes RIXS transitions allowed from all occupied states. A strong influence of the soft x-ray photon diffractional scattering on the RIXS spectral shape is predicted, with the wavelength playing the role of a coherence length of interaction with the electromagnetic field. Due to the excitonic character of photoabsorption transitions near threshold, a resonant structure appears in the RIXS profile above the Fermi level. A strong dependence of the dispersion above the photoabsorption threshold on the strength of the excitonic peak is predicted, with the RIXS band split into two qualitatively different sidebands. The position of the first, main, band is practically independent on the excitation energy for weak excitonic states. The position of the second band, caused by tail excitation of excitonic states, follows the Raman-Stokes dispersion law.