Wave-packet dynamics of resonant x-ray Raman scattering: Excitation near the Cl L-II,L-III edge of HCl

A theory of radiative and nonradiative x-ray Raman scattering based on nucl ear wave-packet dynamics is presented. The theory is evaluated with special emphasis on the cases when the intermediate and/or final state potentials are dissociative. Different "one-step" and "two-step" time-dependent wave-p acket formalisms are proposed and evaluated, giving different interpretatio nal content and computational efficiency. An interference between the molec ular background and the narrow atomiclike contributions is predicted and ev aluated. Due to this interference the atomiclike spectral feature manifests itself as a peak or as a spectral hole depending on the circumstances in t erms of excitation energy, spectral width of incident radiation, and the fo rm of the interatomic potentials. The counterintuitive situation may even a rise that a narrow peak is formed by increasing the spectral photon width. The duration of the resonant x-ray Raman scattering influences in a qualita tively different manner the space distributions of the wave packets in the molecular and the dissociative domains, something that is crucial for the f ormation of the cross section profile. It is shown that the scattering cros s section is proportional to the square of the core excited wave packet and inversely proportional to the derivative of the difference between core ex cited and final state potentials. The atomiclike profile is shown to consis t of a Lorentzian inner part and red or blue wings which give direct inform ation about the long-range regions of the potentials; red wings for divergi ng potentials, and blue for converging. A technique of mapping of the space distribution of the squared core excited wave packet and the interatomic p otentials is suggested. The various features are demonstrated by an ab init io computational study of the resonant Auger spectra of the HCl molecule cl ose to the Cl L-II,L-III edge. [S1050-2947(99)04702-2].