Density functional and spin-orbit Ab initio study of CF₃Br: Molecular properties and electronic curve crossing

Quantum chemical calculations of CF₃Br and the CF₃ radical are performed using density functional theory (DFT) and time-dependent DFT (TDDFT). Molecular structures, vibrational frequencies, dipole moment, bond dissociation energy, and vertical excitation energies of CF₃Br are calculated and compared with available experimental results. The performance of six hybrid and five hybrid meta functionals in DFT and TDDFT calculations are evaluated. The ωB97X, B3PW91, and M05-2X functionals give very good results for molecular structures, vibrational frequencies, and vertical excitation energies, respectively. The ωB97X functional calculates well the dipole moment of CF₃Br. B3LYP, one of the most widely used functionals, does not perform well for calculations of the C - Br bond length, bond dissociation energy, and vertical excitation energies. Potential energy curves of the low-lying excited states of CF₃Br are obtained using the multiconfigurational spin-orbit ab initio method. The crossing point between 2A₁ and 3E states is located near the C - Br bond length of 2.45 Å. Comparison with CH₃Br shows that fluorination does not alter the location of the crossing point. The relation between the calculated potential energy curves and recent experimental result is briefly discussed.