Competition between unimolecular C–Br–bond fission and Br2 elimination in vibrationally highly excited CF2Br2

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Abstract
The competition between C–Br–bond fission and three‐center elimination of molecular bromine (Br2) in highly excited CF2Br2 molecules has been studied under collision‐free conditions. Transient resonantly enhanced multiphoton ionization (REMPI) was used to monitor Br(2P1/2) and Br(2P3/2) formation during and after infrared (IR) multiphoton excitation of CF2Br2; time‐resolved laser‐induced fluorescence (LIF) spectroscopy was employed for the detection of transient CF2 after Br2 elimination. Direct time‐resolved measurements of the sum of afterpulse reaction rates, absolute product yields for the CF2 and Br(2P3/2) channels as well as absorbed energies per excitation pulse were used to characterize parts of the vibrational energy distribution P(E) established after IR multiphoton excitation and to determine rate coefficients and branching ratios for the elimination and dissociation reaction as a function of the average internal energy 〈E〉. The existence of both channels, the dissociation and the elimination channel, has been confirmed. A comparison of the experimental data with statistical adiabatic channel model calculations (SACM) enabled us to determine the threshold energies E0(J=0) for the unimolecular Br2 elimination [E0(J=0)=19 070±500 cm−1] and the C–Br bond fission [E0(J=0)=20 700±500 cm−1], the two possible pathways of the reaction.