Studies On Ionization And Dissociation Processes Of Ethyl Bromide In Intense Femtosecond Laser Field

When the molecules are exposed to a femtosecond laser field with the laser intensities in the range of 1013～1015 W/cm2, this intense femtosecond laser field will modify the potential energy surface (PES) of the electronic state in the molecular systems, and thus a variety of novel physical phenomena will occur, such as multi-photon ionization (MPI), above threshold ionization (ATI), high-order harmonic generation (HHG), Coulomb explosion (CE), and so forth. On the basis of these related phenomena, one can obtain the molecular dynamical processes. Alkyl bromide was usually taken as study example in the field of molecular dynamics under the intense laser field, and its photodissociation behaviors have been regarded as the reference for further understanding the photodissociation dynamics of polyatomic molecules. In this thesis, the multi-photon dissociation and Coulomb explosion of ethyl bromide C2H5Br under near-infrared (800 nm) femtosecond laser field are experimentally investigated by a DC-sliced ion imaging technique, and the main research works are presented as follows.1. We obtained the time of flight mass spectra of ethyl bromide C2HsBr at different laser intensities, and analyzed the dependence of C-C, C-Br and C-H bond fissions on laser intensities and the formation mechanism of high charge ions.2. We investigated the photodissociation process of ethyl bromide C2HsBr under 800-nm intense femtosecond laser field by a DC sliced ion imaging technique, and obtained these fragment ions H2+, CH3+, C2H5+, Br+, CH2Br+ and C2H3Br+ by C-C, C-Br and C-H bond fissions. We assigned the photodissociation dynamical pathways of these fragment ions by calculating their corresponding velocity distributions and angular distributions, and discussed the lifetime of the precursor species in some Coulomb explosion channels.3. We observed the elimination channels of H2 and H2+ in multi-photon dissociation (MPD) and CE processes and theoretically simulated the dissociation pathways by a Ab initio calculations, and the simulation results showed that H2 elimination is an asynchronous concerned reaction while H2+ elimination is a synchronous concerned reaction.