Photodissociation dynamics of CF2Br2

Melanie R. Cameron; Stephen A. Johns; Scott H. Kable

doi:10.1117/12.220866

18 September 1995 Photodissociation dynamics of CF₂Br₂

Melanie R. Cameron, Stephen A. Johns, Scott H. Kable

Proceedings Volume 2548, Laser Techniques for State-Selected and State-to-State Chemistry III; (1995) https://doi.org/10.1117/12.220866
Event: SPIE's 1995 International Symposium on Optical Science, Engineering, and Instrumentation, 1995, San Diego, CA, United States

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 E_vib equals 0.4 kJ mol^-1, E_rot equals 2.4 kJ mol^-1, and E_trans 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 K_a. 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.

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Melanie R. Cameron, Stephen A. Johns, and Scott H. Kable "Photodissociation dynamics of CF₂Br₂", Proc. SPIE 2548, Laser Techniques for State-Selected and State-to-State Chemistry III, (18 September 1995); https://doi.org/10.1117/12.220866

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KEYWORDS

Bromine

Micro optical fluidics

Photolysis

Chemical species

Signal processing

Absorption

Excimer lasers

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