Molecular, spectroscopic and thermochemical characterization of CCl, CF and CBr radicals and related species.

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 CX (with X = F, Cl and Br) and a comparison with the corresponding determinations for the rest of the members of the family CX (with = 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 composite models G3B3 and G4. Structural and spectroscopic characterization of the CF, CCl and CBr radicals, along with the estimation of the enthalpies of formation of CF and CCl, 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 were computed for enthalpies of formation of CF, CCl and CBr, 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 were derived for CF, CCl and CBr, while corresponding values of 0.6 ± 6.3, 228.1 ± 2.1 and 319.6 ± 5.4 kJ mol were estimated for CF, CCl and CBr, respectively.