Matrix Isolation and Computational Study of Isodifluorodibromomethane (F2 Cbr-Br): A Route to Br2 Formation in Cf2 Br2 Photolysis

The photolysis products of dibromodifluoromethane (CF2 Br 2) were characterized by matrix isolation infrared and UV/Visible spectroscopy, supported by ab initio calculations. Photolysis at wavelengths of 240 and 266 nm of CF2 Br2:Ar samples (∼1:5000) held at ∼5 K yielded iso- CF2 Br2 (F2 CBrBr), a weakly bound isomer of CF2 Br2, which is characterized here for the first time. The observed infrared and UV/Visible absorptions of iso- CF2 Br2 are in excellent agreement with computational predictions at the B3LYP/aug-cc-pVTZ level. Single point energy calculations at the CCSD(T)/aug-cc-pVDZ level on the B3LYP optimized geometries suggest that the isoform is a minimum on the CF2 Br2 potential energy surface, lying some 55 kcal/mol above the CF2 Br2 ground state. The energies of various stationary points on the CF2 Br 2 potential energy surface were characterized computationally; taken with our experimental results, these show that iso- CF2 Br 2 is an intermediate in the Br+ CF2 Br→ CF 2 + Br2 reaction. The photochemistry of the isoform was also investigated; excitation into the intense 359 nm absorption band resulted in isomerization to CF2 Br2. Our results are discussed in view of the rich literature on the gas-phase photochemistry of CF2 Br2, particularly with respect to the existence of a roaming atom pathway leading to molecular products. © 2010 American Institute of Physics