Studies On Photodissociation Of Bromine-Containing Compounds Using Ion Velocity Imaging Method

The molecular photodissociation dynamics is a very important part of molecular reaction dynamics, and the study of photodissociation dynamics has been developed to the details of state-to-state reaction with the evolution of the correlative experimental techniques. The important subjects of photodissociation dynamics are that, the specific internal state, alignment and the orientation of the reactants can be prepared, and the internal state, angular and velocity distributions, and the alignment of the products can be measured. With the ion velocity imaging technique all the information (angular and velocity distributions) can be extracted from the spatial appearance of the two-dimensional image detected by a two-dimensional position-sensitive detector. The dissociation channels can be obtained by analyzing the angular and velocity distributions, and the correlative photodissociation dynamics can be investigated in detail. Comparing with the traditional PTS (Photofragment Translation Spectrometry) technique, the ion velocity imaging technique has the advantages that it can be easily realized on a simple experimental apparatus, and its results are'creditable, so that the ion velocity imaging technique has been developed rapidly to be an ideal experiment method for investigating the photodissociation dynamics. In this dissertation, we introduce the details of the homebuilt experimental apparatus, and the research work about the photodissociation dynamics of some alkyl bromides that were accomplished on that. The main works during my PhD studyperiod are as follows:1,The ion velocity imaging experimental apparatus was built with the guidance of the supervisor. By performing the debugging and testing work on the apparatus, we obtained the magnified factor of the apparatus N = 1.04. In addition, the testing results show that the apparatus has satisfied quality, and the data are creditable.2, The branching ratios N(Br^*)/N(Br) of dibromoalkane molecules (CH₂Br₂, C₂H₄Br₂, and C₂H₈Br₂) have been investigated by using resonance-enhanced multiphoton ionization (REMPI) coupled with time of flight mass spectrometry (TOF-MS) near 234 and 267 nm. The branching ratios change with the wavelength of the photolysis laser and the molecular structures, and we obtained the correlation between the branching ratios and the potential energy surfaces by analyzing the changing trends: (1) The velocity at curve crossing region of CH₂Br₂ is found faster than that of C₂H₄Br₂, which results in an decreased non-adiabatic transitions and smaller Br of C₂H₂Br₂; (2) The cI) Br of CH₂Br₂ and C₂H₂Br₂ were found to increase with photon energy, while the C₂H₄Br₂ shows a contrary trend during photodissociation. An explanation for the different trends is that there exists larger avoided curve crossing for the lower symmetry of C₄HsBr₂, and it will influence the dissociation channels during the photodissociation process.3,The photodissociation dynamics of dibromomethane (CHzBr₂) has been studied near 234 and 267 nm. The anisotropy parameter fland translational energy...