Photodissociation of CF/sub 2/BrCH/sub 2/I at 248, 266, and 308 nm
The technique of photofragmentation translational spectroscopy has been usedto study the photodissociation of CF/sub 2/BrCH/sub 2/I at excitation wavelengths of 248, 266, and 308 nm. The primary photofragments are CF/sub 2/BrCH/sub 2/ and eitherI(/sup 2/P/sub 1//sub ///sub 2/) or I(/sup 2/P/sub 3//sub ///sub 2/), although some C--Br bond fission does occur at 248 and 266 nm. A large fraction of the CF/sub 2/BrCH/sub 2/ radical product contains enough internal excitation after the primary process to undergo secondary dissociation into CF/sub 2/CH/sub 2/ and Br. Secondary dissociation is also observed to take place at 248 and 266 nm via absorption of a photon by the CF/sub 2/BrCH/sub 2/ photofragment. By observing the threshold for the spontaneous secondary dissociation process, the reaction enthalpy for CF/sub 2/BrCH/sub 2/I..-->..CF/sub 2/CH/sub 2/ + Br + I, was determined to be 67.5 +- 2 kcal/mol, which leads to: ..delta.. H/sup circle-open//sub f//sub ,0/ (CF/sub 2/BrCH/sub 2/I) = -92.6 +- 2 kcal/mol. The c.m. translational energy distributions were derived for both the I(/sup 2/P/sub 1//sub ///sub 2/) and I(/sup 2/P/sub 3//sub ///sub 2/) dissociation channels resulting from primary C--I bond breakage. The I(/sup 2/P/sub 1//sub ///sub 2/)/I(/sup 2/P/sub 3//sub ///sub 2/) branching ratios are 3.3, 9.0, and 0.5 for excitation wavelengths of 248, 266, and 308 nm, respectively. The translational energy distributions also reveal that a major fraction of the CF/sub 2/BrCH/sub 2/ product radicals are formed with high internal energies, averaging around 50% of the excess energy.
- Research Organization:
- Materials and Molecular Research Division, Lawrence Berkeley Laboratory and Department of Chemistry, University of California, Berkeley, California 94720
- OSTI ID:
- 7042062
- Journal Information:
- J. Chem. Phys.; (United States), Journal Name: J. Chem. Phys.; (United States) Vol. 86:4; ISSN JCPSA
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
400500* -- Photochemistry
BRANCHING RATIO
BROMINATED ALIPHATIC HYDROCARBONS
CHEMICAL BONDS
CHEMICAL REACTIONS
DECOMPOSITION
DISSOCIATION
DISSOCIATION HEAT
ELECTROMAGNETIC RADIATION
ENTHALPY
FLUORINATED ALIPHATIC HYDROCARBONS
FORMATION HEAT
HALOGENATED ALIPHATIC HYDROCARBONS
IODINATED ALIPHATIC HYDROCARBONS
ORGANIC BROMINE COMPOUNDS
ORGANIC COMPOUNDS
ORGANIC FLUORINE COMPOUNDS
ORGANIC HALOGEN COMPOUNDS
ORGANIC IODINE COMPOUNDS
PHOTOCHEMICAL REACTIONS
PHOTOLYSIS
PHYSICAL PROPERTIES
RADIATIONS
REACTION HEAT
THERMODYNAMIC PROPERTIES
ULTRAVIOLET RADIATION