Molecular, spectroscopic and thermochemical characterization of C 2 Cl 3 , C 2 F 3 and C 2 Br 3 radicals and related species

Abstract

This work reports a detailed theoretical study of the molecular parameters, harmonic vibrational frequencies, UV absorption spectra and standard enthalpies of formation for the radicals C2X3 (with X = F, Cl and Br) and a comparison with the corresponding determinations for the rest of the members of the family C2Xn (with n = 2-4). Molecular properties were calculated using different levels of theory: density functional theory employing the B3LYP, X3LYP, BMK, M06-2X and M08-HX functionals combined with the basis sets 6?311++G(3df,3pd) and aug-cc-pVTZ, and the ab initio composite models G3B3 and G4. Structural and spectroscopic characterization of the C2F3, C2Cl3 and C2Br3 radicals, along with the estimation of the enthalpies of formation of C2F3 and C2Cl3, were derived here for the first time, to our knowledge. In particular, values of −220.9 ± 2.9, 230.8 ± 3.8 and 375.4 ± 5.9 kJ mol−1 were computed for enthalpies of formation of C2F3, C2Cl3 and C2Br3, respectively. Additionally, enthalpies of formation for related closed-shell molecules were obtained with less uncertainty compared to those found in the literature. The recommended values of −669.6 ± 3.8, −23.0 ± 4.6 and 155.3 ± 5.0 kJ mol−1 were derived for C2F4, C2Cl4 and C2Br4, while corresponding values of 0.6 ± 6.3, 228.1 ± 2.1 and 319.6 ± 5.4 kJ mol−1 were estimated for C2F2, C2Cl2 and C2Br2, respectively.