title: Photodissociation dynamics of bromofluorobenzenes using velocity imaging technique.
abstract: Velocity imaging technique combined with (2 + 1) resonance-enhanced multiphoton ionization (REMPI) has been used to detect the Br fragment in photodissociation of o-, m-, and p-bromofluorobenzene at 266 nm. The branching ratio of ground state Br(2P3/2) is found to be larger than 96%. Its translational energy distributions suggest that the Br fragments are generated via two dissociation channels for all the molecules. The fast route, which is missing in p-bromofluorobenzene detected previously by femtosecond laser spectroscopy, giving rise to an anisotropy parameter of 0.50-0.65, is attributed to a direct dissociation from a repulsive triplet T1(A' ') or T1(B1) state. The slow one with anisotropy parameter close to zero is proposed to stem from excitation of the lowest excited singlet (pi,pi*)state followed by predissociation along a repulsive triplet (pi,sigma*) state localized on the C-Br bond. For the minor product of spin-orbit excited state Br(2P1/2), the dissociating features are similar to those found in Br(2P3/2). Our kinetic and anisotropic features of decomposition obtained in m- and p-bromofluorobenzene are opposed to those by photofragment translational spectroscopy. Discrepancy between different methods is discussed in detail.
authors.affiliation: State Key Laboratory of Magnetic Resonance and Atomic and Molecular Physics, Wuhan Institute of Physics and Mathematics, Chinese Academy of Sciences, Wuhan 430071, P. R. China.
authors.forename: Ying
authors.initials: Y
authors.lastname: Tang
authors.forename: Wei-Bin
authors.initials: WB
authors.lastname: Lee
authors.forename: Bing
authors.initials: B
authors.lastname: Zhang
authors.forename: King-Chuen
authors.initials: KC
authors.lastname: Lin
mesh_terms: D016880:Anisotropy; D006846:Hydrocarbons, Halogenated / Q000737:chemistry* / Q000528:radiation effects; D007091:Image Processing, Computer-Assisted / Q000379:methods*; D007700:Kinetics; D007834:Lasers; D036641:Microscopy, Fluorescence, Multiphoton / Q000379:methods; D010777:Photochemistry; D011789:Quantum Theory; D021241:Spectrometry, Mass, Electrospray Ionization / Q000379:methods; D013997:Time Factors
chemical_list: D006846:Hydrocarbons, Halogenated