An ab Initio Investigation of Fluorobromo Carbene

Fluorobromo carbene, an important halogenated carbene in the stratospheric ozone depletion, has long been received considerable interest. However, the energy, structure, and dynamics of even the lowest excited states have not been well understood. In this paper, we performed a detail ab initio study on CFBr using complete active space second-order perturbation (CASPT2) and multireference configuration interaction (MRCI) method. We investigated the effect of basis set on the CASPT2 results of the ground X1A′ state and the first excited singlet A1A″ state. The potential energy surface (PES) of the A1A″ state along C–Br bond distance was carefully examined at CASPT2/cc-pV5Z level, by optimizing C–F bond and F–C–Br angle at every C–Br bond length in contrast to fix them at the equilibrium values. On the basis of the PES, a reliable barrier height of the A1A″ state was obtained from CASPT2 and MRCI+Q calculations with different basis sets, considering the scalar relativistic effect, spin–orbit coupling, and core–valence correlation. Finally, we carried out the first theoretical study on higher excited state with energy up to 7 eV. The present calculated results were compared with previous experimental and theoretical results where available. Our results will add some understanding and shed more light on the structure and dynamics of electronic states of CFBr radical.