Studies On Ionization And Dissociative Processes Of Halogenated Hydrocarbon Irradiated By Femtosecond Laser Field

With the development of femtosecond laser technology, the interaction of molecule (atom) system with femtosecond laser field has attracted more and more attention, many new physical phenomena have been theoretically predicted and experimentally observed, including of high harmonic generation (HHG), above threshhold ionization (ATI), multi-photon ionization dissociation (MPID) and Coulomb Explosion (CE) etc. Some new technologies, including of time-flight mass spectrum, veloctiy mapping imaging, etc., have been introduced to investigate the above-mentioned physical and chemical processes in detail. Due to the important role in the atmospheric physics and chemistry, Halogenated hydrocarbon molecules have been studied intensively and extensively. In this dissertation, we mainly focused on the ionization and dissociation processes of halogenated hydrocarbon molecules irradiated by an intense femtosecond laser field (1013～1014W/cm2), and the wave-packet dynamics of the excited states, being important to the molecular ionization and dissociation processes, has been also studied in the dichloro-fluorescein molecule. The detail as follow:1) The dissociative double ionization (DDI) and multi-photon ionization (MPI) of1-bromo-2-chloroethane (BCE) irradiated by the800nm femtosecond laser field have been investigated by dc-slice imaging technology. The doubly charged parent ion ratio [BCE2+]/[BCE+] were measured, and the corresponding double ionization processes including of non-sequential double ionization (NSDI) and sequential double ionization (SDI) were analyzed. The sliced images of different photo-dissociated ions were detected, and the corresponding KER distributions were extracted. Furthermore, the dissociative double ionization channels, attributed to the cleavage of the C-C, C-Br and C-Cl bonds by the Coulombic repulsive forces, were discussed, and the revised equilibrium distance Re*, the energy ratio Eexp/Ecoul and the value were calculated.2) The ionization and dissociation processes of molecule1-fluo-2-bromoethane (FBE) irradiated by the800nm femtosecond laser field have been investigated by dc-slice imaging technology. The ionization mechnisam of FBE molecule in different laser intentsities has been analyzed experimentally and thorectically. The slicecd images and corresponding KER distributions of the produced fragments have been obtained, and the related reaction channels have been proposed based on the calcaulations by Gaussian09software packages. The dehydrogenation influences on the DDI channels have been discussed and analyzed in the KER and angular distributions and the photo fragments yields. Furthermore, it is found that DDI and MPDI processes are competitive in the C-C and C-Br bond cleavage.3) The dynamics of molecular excited vibrational states have an important role in molecular ionization and dissociation process. Based on the femtosecond laser phase-locking, the excited vibrational wavepacket dynamics of dichloro-fluorescein have been investigated. The coherently constructive and destructive interferences have been experimentally observed, and its period is measured to be about230fs. It will provide a new experimental method to coherently manipulate the molecular ionization and dissociation process by the molecular vibrational wave packet interference.