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Proceedings Paper

Photodissociation dynamics of CF2Br2
Author(s): Melanie R. Cameron; Stephen A. Johns; Scott H. Kable
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Paper Abstract

The photodissociation dynamics of CF2Br2, producing the CF2 radical, have been studied at six photolysis wavelengths: 218, 223, 238, 246, 266, and 274 nm. For a photolysis wavelength of 246 nm, the average energy of each of the CF2 degrees of freedom was measured as Evib equals 0.4 kJ mol-1, Erot equals 2.4 kJ mol-1, and Etrans equals 25 kJ mol-1 for a total average CF2 energy of 28 plus or minus 6 kJ mol-1. The distribution of rotational states showed a preference for low Ka. Three possible pathways were considered for the formation of CF2: (1) CF2Br2 plus h(nu) yields CF2 plus Br2; (2) CF2Br2 plus h(nu) yields CF2 plus 2 Br; and (3) CF2Br2 plus h(nu) yields CF2Br plus Br; CF2Br plus h(nu) yields CF2 plus Br. It was found that neither reaction (1) nor reaction (3) satisfied conservation of energy given the observed energy distribution in CF2. Hence reaction (2) was concluded as responsible for the formation of the CF2. Possible mechanisms for this reaction were considered, including stepwise and concerted production of the three fragments. However, neither mechanism was found to be in accord with the experimental observations. The concerted mechanism seemed to fail to account for the observed J/K correlation of the nascent CF2 (favoring in-plane rotation). The stepwise reaction is not consistent with the non-statistical behavior of the nascent product. A concerted mechanism was re-evaluated based on low level ab initio quantum mechanical calculations. These calculations showed that the lowest energy transition for CF2Br2 reaction is planar. If the elimination of the two bromine atoms occurs in-plane, asymmetrically, then this geometry may be used to describe the experimental results.

Paper Details

Date Published: 18 September 1995
PDF: 11 pages
Proc. SPIE 2548, Laser Techniques for State-Selected and State-to-State Chemistry III, (18 September 1995); doi: 10.1117/12.220866
Show Author Affiliations
Melanie R. Cameron, Univ. of Sydney (Australia)
Stephen A. Johns, Univ. of Sydney (Australia)
Scott H. Kable, Univ. of Sydney (Australia)

Published in SPIE Proceedings Vol. 2548:
Laser Techniques for State-Selected and State-to-State Chemistry III
John W. Hepburn, Editor(s)

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