Studies On Photodissociation Mechanisms Of Some Typical Halogenated Compounds

The photodissociation of molecules are one of the most important and primary processes in photochemical reactions. The studies on the photodissociation dynamics are helpful not only to obtain the information on the excited states of the molecules but also to understand the nature of the fundamental reactions. In this dissertation, we have investigated the photodissociation mechanisms of some typical Halogenated compounds using the ion velocity imaging and relevant techniques. The main work is summarized as following:(1) The photodissociation dynamics of 1-Iodopropane (1-C₃H₇I) and 2-Iodopropane (2-C₃H₇I) at 267nm have been investigated with the ion images of the photofragments I(²P_3/2) and I^*(²P_1/2). The results indicate that, with the radical on a-carbon atom being more branched, the probabilities to form the I(²P_3/2) fragments obviously increase and the energy distribution of the photoproducts become visibly wider; for the same molecule, the energy distributions of the I(²P_3/2) channels are wider than those of the I^*(²P_1/2) channels while the corresponding angular distributions are weaker than those of I^*(²P_1/2) channels.(2)The fission mechanisms of the C-Br bonds of 2-bromothiophene and 3-bromothiophene at 267nm have been investigated using ion velocity imaging technique. The results indicate that there exist three possible pathways for the fission of the C-Br bonds: (i) the fast predissociation via the transition from the singlet excited state to the triplet excited state, (ii) the thermal dissociation via the radiationless transition from the singlet excited state to the highly vibrational ground state and (iii) the fragmentation of the parent ions produced by multiphoton absorption, and with the position of Br atom in the thienyl being far from sulphur atom, the relative ratios of products from the channel (i) and the channel (ii) decrease obviously and the corresponding anisotropy of each pathway weaker.(3) The dissociative behaviors of the Chlorobromometnane (CH₂BrCl) have been investigated using femtosecond pump-probe technique. It is found that the main photoproducts of the molecule are CH₂Cl⁺,CH₂Br⁺ and CH₂BrCl⁺. The dissociation lifetime of the A-band for the parent molecule is obtained and the mechanisms to form the fragment ions are discussed.