DFT study on the one-electron reduction of CF3X (X = Cl, Br, I) molecules

We present the DFT study on several aspects of the process of one-electron attachment to the CF3X molecules accompanied by CX bond dissociation. Three functionals, B3PW91, MPW1PW91 and PBE1PBE, combined with 6-31 + G*, 6-311 + G* and AUG-cc-pVTZ basis sets were used. Dipole moments and adiabatic electron affinities of neutral molecules as well as structural and energetic properties of both forms obtained from the calculations are compared to experimental data. Averaged electron affinity values of 0.45 eV (CF3Cl), 0.89 eV (CF3Br) and 1.26 eV (CF3I) are obtained from the DFT/AUG-cc-pVTZ results. Structural properties of meta-stable anions formed in the gas-phase are found to depend weakly on the X atom, except for the CX bond lengths, for which we propose dCX values of 2.615 Å for CF3Cl−, 2.733 Å for CF3Br− and 2.911 Å for CF3I−. All harmonic vibrational frequencies are much lower in anions than in molecules. For the radical anions the larger basis sets yield almost identical CCl and CI dissociation energies (∼0.48 eV with AUG-cc-pVTZ), while CBr energy is smaller by about 0.03 eV. The smallest basis set suggests similar values but opposite order, i.e. CBr bond is the strongest, followed by CCl and the weakest CI. The dissociation energies and electron affinities are compared with results obtained with the Gn and CBS-QB3 methods. Average energy barriers for the gas-phase reduction process obtained from the intersection of AUG-cc-pVTZ potential energy profiles for the molecules and anions are equal to: 0.34 eV (CF3Cl), 0.23 eV (CF3Br) and 0.13 eV (CF3I).