Matrix isolation and computational study of isodifluorodibromomethane (F2CBr–Br): A route to Br2 formation in CF2Br2 photolysis

摘要

The photolysis products of dibromodifluoromethane (CF2Br2) were characterized by matrix isolation infrared and UV/Visible spectroscopy, supported by ab initio calculations. Photolysis at wavelengths of 240 and 266 nm of CF2Br2:Ar samples ( ∼ 1:5000) held at ∼ 5 K yielded iso-CF2Br2 (F2CBrBr), a weakly bound isomer of CF2Br2, which is characterized here for the first time. The observed infrared and UV/Visible absorptions of iso-CF2Br2 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 CF2Br2 potential energy surface, lying some 55 kcal/mol above the CF2Br2 ground state. The energies of various stationary points on the CF2Br2 potential energy surface were characterized computationally; taken with our experimental results, these show that iso-CF2Br2 is an intermediate in the Br+CF2Br→CF2+Br2 reaction. The photochemistry of the isoform was also investigated; excitation into the intense 359 nm absorption band resulted in isomerization to CF2Br2. Our results are discussed in view of the rich literature on the gas-phase photochemistry of CF2Br2, particularly with respect to the existence of a roaming atom pathway leading to molecular products. © 2010 American Institute of Physics Article Outline INTRODUCTION EXPERIMENTAL AND THEORETICAL METHODS RESULTS AND DISCUSSION Matrix IR spectroscopy and computational studies of iso- CF2Br2 Comparison of matrix IR results with previous work Electronic spectroscopy and photochemistry of iso- CF2Br2 Comparison of matrix and gas-phase photochemistry of CF2Br2 CONCLUSIONS