The Ionization And Dissociation Of Brominated Compounds In The Femtosecond Laser Field

With the development of ultrafast femtosecond laser technology,more and more novel phenomena during the light-matter interaction,such as multi-electron ionization,high-harmonic generation,attosecond laser pulse generation and Coulomb explosion,have been observed and investigated.With the help of the advanced vacuum particle detection technique,one can directly obtain the information of the momentum and energy of the dissociated electrons and ions as well as their correlation information,as a result,obtain the molecular structural dynamics on femtosecond time scale and the electron dynamics on attosecond time scale.This will help us to understand the fundamental principle of light-matter interaction.In the dissertation,by using the time-of-flight and dc-sliced ion velocity map imaging technology,the ionization,dissociation and Coulomb explosion of a series of brominated compounds in the femtosecond laser field have been investigated.After analyzing the yield,energy and angular distribution of the produced fragments,combing with the high-level quantum chemical calculation,the different chemical reaction channels have been resolved.The selective excitation of some special reaction channels has been achieved,and the relationship between ion(s)ejection direction and the coupling of the corresoponding excited states has been revealed.Moreover,the enhanced ionization mechanism of multi-electron ionization process has been proposed.In addition,the related studies are not only the frontier exploration of strong-field ionization and dissociation dynamics in complicated polyatomic molecule system,but providing the experimental support of air pollution prevention and ozone destruction control.The details are as follows,1.The ionization and dissociation of molecular Bromocyclopropane(BCP) in 800 nm femtosecond laser field has been studied,and the ring-open process in intense laser field has been observed.By analyzing the kinetic energy release and angular distribution,the different dissociation reaction channels and the dehydrogenation mechanism during the Coulomb explosion have been revealed.2.The dissociative ionization processes of CF₂Br2 molecule in the 800 and 400 nm laser fields have been investigated.The dissociation channels along C-Br bond cleavage have been determined.The results indicate that the isotropic feature of the angular distribution for CF₂Br⁺ ions is attributed to the coupling between the excited states.Additionally,a unique asynchronous elimination channel of CF₂Br₂⁺?CF₂ + Br₂⁺ has been only observed under the 400 nm laser field excitation.3.The dissociation and Coulomb explosion of CHBrCl₂ molecule in an intense laser field have been studied.By analyzing the fragments yield dependency of laser intensity,two dissociation channels involving the cleavage of C-Cl and C-Br bond has been revealed.Moreover,two-body Coulomb explosion and dissociation channels of the parent molecular ions have been determined with the analysis of kinetic energy release and angular distributions.And the classic point charge Coulomb explosion model has been improved.4.The multi-electron and Coulomb explosion of molecular IBr in 800 nm laser field have been investigated.By analyzing the yield,kinetic energy release and angular distribution of different charge states fragment ions,the relationship of electron density distribution of molecular orbitals and ejection direction of fragment ions has been revealed.Based on the ‘ladder-type' ionization model,the correlation between nuclear motion and multi-electron enhancement ionization has been explored and four ionization pathways have been determined.Meanwhile,the charge asymmetrical dissociation and charge transfer have also been discussed.