Quantum nuclear dynamics in  x-ray scattering and lasing

Detta är en avhandling från Stockholm : KTH

Sammanfattning: This thesis presents a theoretical study of the role of nuclear degrees of freedom in the x-ray absorption, x-ray resonant scattering  and some aspects of the interaction of matter with strong laser fields. Most numerical simulations are performed with a time-dependent wave-packet program that have proved its robustness  in previous investigations. The relevant experimental results are also presented for comparison when available.The first problem considered in the thesis is the possibility of obtaining x-ray absorption spectra with resolution beyond the natural lifetime broadening of the core-excited electronic states. It is shown that the method of measuring x-ray absorptionin the resonant scattering mode suggested earlier for that purpose exhibits severe limitations originating from the lifetime vibrational interference between the intermediate core-excited vibrational levels. However, a broad class of molecules is found for which spectra with super-high resolution can indeed be obtained. These molecules have parallel potential energy surfaces of the core-excited and final states for the x-ray scattering process.The interpretations of two interesting cases of x-ray absorption and Auger scattering follow. The first one is related to scattering through a doubly excited ? state in the CO molecule. A Doppler split feature near 299.4 eV and strong scattering anisotropy are  observed. Both features are well explained and reproduced by the theory. Next, theelectron-vibrational fine structure of the excitation for O2 is investigated by means of different models. We are able to single out the electronic states and interpotential crossing points responsible for the peculiar absorption profile. Based on these findings we explain and reproduce the x-ray Auger scattering spectra through the same excitation. Here we encounter a rather unusual situation in which the Auger spectra are affected by three types of the interference: Apart from the lifetime vibrational interference, a strong interference between two intermediate electronic states and an interference with the direct-scattering amplitude is also present.The process of intramolecular vibrational redistribution (IVR) is investigated in the context of formation of amplified spontaneous emissions (ASE) inside laser-pumped gain media. IVR raises to a higher energy region the threshold pump intensity after which blue-shifted ASE is observed.Finally, we suggest a new scheme of x-ray pump-probe spectroscopy based on the core-hole hopping in N2 induced by an infrared laser field. We investigate the result from the core-hole hoping on the vibrational structure of the x-ray absorption profile. Furthermore, by populating core-excited states with opposite parities, the laser field opens up symmetry forbidden resonant inelastic scattering channels, which can give new insights about the electronic structure of matter.