Br{sub 2} molecular elimination in 248 nm photolysis of CHBr{sub 2}Cl by using cavity ring-down absorption spectroscopy

Journal Article · Sun Jan 21 04:00:00 EST 2007 · Journal of Chemical Physics

DOI:https://doi.org/10.1063/1.2426334· OSTI ID:20868216

Peiying, Wei; Yuanping, Chang; Yushan, Lee; Weibin, Lee; Kingchuen, Lin; Chen, K T; Chang, A H. H. ^[1]

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1. Department of Chemistry, National Taiwan University, Taipei 106, Taiwan and Institute of Atomic and Molecular Sciences, Academia Sinica, Taipei 106, Taiwan (China)

Elimination of molecular bromine is probed in the B {sup 3}{pi}{sub ou}{sup +}<-X {sup 1}{sigma}{sub g}{sup +} transition following photodissociation of CHBr{sub 2}Cl at 248 nm by using cavity ring-down absorption spectroscopy. The quantum yield for the Br{sub 2} elimination reaction is determined to be 0.05{+-}0.03. The nascent vibrational population ratio of Br{sub 2}(v=1)/Br{sub 2}(v=0) is obtained to be 0.5{+-}0.2. A supersonic beam of CHBr{sub 2}Cl is similarly photofragmented and the resulting Br atoms are monitored with a velocity map ion-imaging detection, yielding spatial anisotropy parameters of 1.5 and 1.1 with photolyzing wavelengths of 234 and 267 nm, respectively. The results justify that the excited state promoted by 248 nm should have an A{sup ''} symmetry. Nevertheless, when CHBr{sub 2}Cl is prepared in a supersonic molecular beam under a cold temperature, photofragmentation gives no Br{sub 2} detectable in a time-of-flight mass spectrometer. A plausible pathway via internal conversion is proposed with the aid of ab initio potential energy calculations. Temperature dependence measurements lend support to the proposed pathway. The production rates of Br{sub 2} between CHBr{sub 2}Cl and CH{sub 2}Br{sub 2} are also compared to examine the chlorine-substituted effect.

• OSTI ID: 20868216
• Journal Information: Journal of Chemical Physics, Journal Name: Journal of Chemical Physics Journal Issue: 3 Vol. 126; ISSN JCPSA6; ISSN 0021-9606
• Country of Publication: United States
• Language: English

Related Subjects

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY
ABSORPTION SPECTROSCOPY
BROMINATED ALIPHATIC HYDROCARBONS
BROMINE
CHLORINATED ALIPHATIC HYDROCARBONS
DISSOCIATION
EXCITED STATES
MASS SPECTRA
MOLECULAR BEAMS
PHOTOCHEMISTRY
PHOTOLYSIS
PHOTON-MOLECULE COLLISIONS
POTENTIAL ENERGY
REACTION KINETICS
TEMPERATURE DEPENDENCE
TIME-OF-FLIGHT MASS SPECTROMETERS
TIME-OF-FLIGHT METHOD