Studies On Photodissociation Dynamics Of Bromides Using Ion Velocity Imaging Method

Photodissociation of bromides has been a popular area of investigation, in view of their ozone depletion potential and of the fundamental interest in photodissociation dynamics. The substituting of different radicals in the photodissociation dynamics of bromides has distinct effect. Such as the photolysis of the alkyl halides is a direct dissociation, and the photolysis of heterocyclic aromatic is proposed to be a predissociation.The method of ion velocity imaging is used to obtain the angular and velocity distributions extracted from the spatial appearance of the velocity image detected by a two-dimensional position-sensitive detector. Comparing with the traditional 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 visual. So it is an ideal experiment method for the photodissociation dynamics.In this dissertation, we introduce the details of the experimental apparatus, and the research work about the Photodissociation dynamics of the alkyl halides (octyi bromide) and the heterocyclic aromatic (3-bromopyridine).1,The Photodissociation dynamics of octyl bromide (C₈H₁₇Br) with excitation laser at 234nm has been studied using ion velocity imaging. The relative quantum yields are obtained from (2＋1) resonance-enhanced multiphoton ionization (REMPI) of the photofragment Br(2^P_1/2) andBr(2^P_3/2). The velocity maps provide detailed information on translational energy distributions and angular distributions. The probabilities of the individual pathways of the fragments are calculated from the relative quantum yield and angular distribution. The results indicate that the dissociation from (n o) states directly and a large fraction of the available energy translates into the internal energy of the fragments. This energy partition correlates with the alkyl structure, refer to the soft impulsive model.2,The photodissociation dynamics of 3-bromopyridine has been investigated near 234 and 266nm. The Br fragments have three modal velocity distributions, while thc Br* fragments show one velocity distribution on the contrary. The high ldnctic energy Br atoms are ascribed to the predissociation from (ππ*) state to the repulsive (n o*) state, and the dissociation from (n o*) states directly; while the minor low kinetic energy Br atoms are attributed to the internal conversion of the (ππ*) state.