Density functional and ab initio investigation of CF2ICF2I and CF2CF2I radicals in gas and solution phases

Quantum chemical calculations of CF(2)ICF(2)I and (*)CF(2)CF(2)I, model systems in reaction dynamics, in the gas phase and methanol solvent are performed using the density functional theory (DFT) and multiconfigurational ab initio methods. Molecular geometries, vibrational frequencies, and vertical excitation energies (T(v)) are computed and compared with available experimental results. We also evaluate the performance of four hybrid and one hybrid meta DFT functionals. The T(v) values calculated using time-dependent DFT vary depending on the exchange-correlation functionals, with the degree of variation approaching approximately 0.7 eV. The M05-2X functional well predicts molecular geometries and T(v) values, while it overestimates the vibrational frequencies. The T(v) values calculated using the M05-2X are similar to those calculated by the CASPT2. All low-lying excited states in CF(2)ICF(2)I are characterized by the excitation from the nonbonding to antibonding orbital of C-I. The excited states of (*)CF(2)CF(2)I are different in their character from those of CF(2)ICF(2)I and have considerable double excitation characters. The spin-orbit coupling of (*)CF(2)CF(2)I is larger than that of CF(2)ICF(2)I.