F. Gelmukhanov et H. Agren, SPECTRAL FEATURES OF RESONANT RADIATIVE X-RAY RAMAN-SCATTERING BY POLYMERS AND SOLIDS, Physical review. B, Condensed matter, 57(5), 1998, pp. 2780-2792
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.