Elimination mechanisms of Br{sub 2}{sup +} and Br{sup +} in photodissociation of 1,1- and 1,2-dibromoethylenes using velocity imaging technique

Journal Article · Sat May 21 00:00:00 EDT 2011 · Journal of Chemical Physics

DOI:https://doi.org/10.1063/1.3584178· OSTI ID:21560247

Linqiang, Hua; Bing, Zhang ^[1]; Lee, Wei-Bin; Chao, Meng-Hsuan; Lin, King-Chuen ^[2]

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1. State Key Laboratory of Magnetic Resonance and Atomic and Molecular Physics, Wuhan Institute of Physics and Mathematics, Chinese Academy of Sciences, Wuhan 430071 (China)
2. Department of Chemistry, National Taiwan University, Taipei 106, Taiwan (China) and Institute of Atomic and Molecular Sciences, Academia Sinica, Taipei 106, Taiwan (China)

Elimination pathways of the Br{sub 2}{sup +} and Br{sup +} ionic fragments in photodissociation of 1,2- and 1,1-dibromoethylenes (C{sub 2}H{sub 2}Br{sub 2}) at 233 nm are investigated using time-of-flight mass spectrometer equipped with velocity ion imaging. The Br{sub 2}{sup +} fragments are verified not to stem from ionization of neutral Br{sub 2}, that is a dissociation channel of dibromoethylenes reported previously. Instead, they are produced from dissociative ionization of dibromoethylene isomers. That is, C{sub 2}H{sub 2}Br{sub 2} is first ionized by absorbing two photons, followed by the dissociation scheme, C{sub 2}H{sub 2}Br{sub 2}{sup +}+ hv{yields}Br{sub 2}{sup +}+ C{sub 2}H{sub 2}. 1,2-C{sub 2}H{sub 2}Br{sub 2} gives rise to a bright Br{sub 2}{sup +} image with anisotropy parameter of -0.5 {+-} 0.1; the fragment may recoil at an angle of {approx}66 deg. with respect to the C = C bond axis. However, this channel is relatively slow in 1,1-C{sub 2}H{sub 2}Br{sub 2} such that a weak Br{sub 2}{sup +} image is acquired with anisotropy parameter equal to zero, indicative of an isotropic recoil fragment distribution. It is more complicated to understand the formation mechanisms of Br{sup +}. Three routes are proposed for dissociation of 1,2-C{sub 2}H{sub 2}Br{sub 2}, including (a) ionization of Br that is eliminated from C{sub 2}H{sub 2}Br{sub 2} by absorbing one photon, (b) dissociation from C{sub 2}H{sub 2}Br{sub 2}{sup +} by absorbing two more photons, and (c) dissociation of Br{sub 2}{sup +}. Each pathway requires four photons to release one Br{sup +}, in contrast to the Br{sub 2}{sup +} formation that involves a three-photon process. As for 1,1-C{sub 2}H{sub 2}Br{sub 2}, the first two pathways are the same, but the third one is too weak to be detected.

• OSTI ID: 21560247
• Journal Information: Journal of Chemical Physics, Vol. 134, Issue 19; Other Information: DOI: 10.1063/1.3584178; (c) 2011 American Institute of Physics; ISSN 0021-9606
• Country of Publication: United States
• Language: English

Related Subjects

74 ATOMIC AND MOLECULAR PHYSICS
37 INORGANIC
ORGANIC
PHYSICAL AND ANALYTICAL CHEMISTRY
ANISOTROPY
BROMINE
BROMINE IONS
DISSOCIATION
DISTRIBUTION
IMAGES
ISOMERS
MASS SPECTRA
MULTI-PHOTON PROCESSES
ORGANIC COMPOUNDS
PHOTOCHEMISTRY
PHOTOIONIZATION
PHOTOLYSIS
PHOTON-MOLECULE COLLISIONS
PHOTONS
RECOILS
TIME-OF-FLIGHT MASS SPECTROMETERS
TIME-OF-FLIGHT METHOD
VELOCITY
BOSONS
CHARGED PARTICLES
CHEMICAL REACTIONS
CHEMISTRY
COLLISIONS
DECOMPOSITION
DYNAMIC MASS SPECTROMETERS
ELEMENTARY PARTICLES
ELEMENTS
HALOGENS
IONIZATION
IONS
MASS SPECTROMETERS
MASSLESS PARTICLES
MEASURING INSTRUMENTS
MOLECULE COLLISIONS
NONMETALS
PHOTOCHEMICAL REACTIONS
PHOTON COLLISIONS
SPECTRA
SPECTROMETERS
TIME-OF-FLIGHT SPECTROMETERS