COLLAPSE OF VIBRATIONAL STRUCTURE IN SPECTRA OF RESONANT X-RAY RAMAN-SCATTERING

Extreme narrowing, or collapse, of electron-vibrational bands is predi cted as a new phenomenon in resonant radiative and nonradiative x-ray scattering (RXS) spectra. It is shown that in the inelastic scattering case, that is, when the potential surfaces of ground and final slates are different, a considerable narrowing of the vibronic RXS band resu lts from detuning the excitation Photon frequency omega away from the absorption resonance. By fine tuning the frequency, this may under spe cial circumstances also occur in the region of strong photoabsorption. In the case of elastic Rayleigh scattering, that is, when the potenti al surfaces of ground and final states are identical, the narrowing re sults in a total collapse to a single resonance by detuning the freque ncy. The theory predicts how the differencies in vibrational structure of resonant and nonresonant photoemission spectra depends on the exci tation frequency. The effect of frequency detuning on complex spectral multilevel structures due to multiplet: and spin-orbit splittings is discussed qualitatively. It is shown that the notion of: duration time for the x-ray scattering process plays a crucial role in the understa nding of RXS spectra.