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 omega B97X, B3PW91, and M05-2X functionals give very good results for molecular structures, vibrational frequencies, and vertical excitation energies, respectively. The omega B97X 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 2A(1) and 3E states is located near the C-Br bond length of 2.45 angstrom. 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.