Density functional and ab initio investigation of CF₂ICF ₂I and CF₂CF₂I radicals in gas and solution phases

Quantum chemical calculations of CF₂ICF₂I and ^•CF₂CF₂I, 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 ∼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 ₂ICF₂I are characterized by the excitation from the nonbonding to antibonding orbital of C-I. The excited states of ^•CF₂CF₂I are different in their character from those of CF₂ICF₂I and have considerable double excitation characters. The spin-orbit coupling of ^•CF ₂CF₂I is larger than that of CF₂ICF ₂I.