Chlorine nuclear quadrupole coupling in chlorodifluoroacetyl chloride: Theory and experiment

A potential energy scan of chlorodifluoroacetyl chloride, CF₂ClC(O)Cl, at the MP2/6-311+G(d) level of theory predicts stable gauche and trans conformers, with E_gauche<E_trans. Ab initio calculations were made of approximate equilibrium structures of these and, on these structures, calculations were made of ³⁵Cl and ³⁷Cl nuclear quadrupole coupling constant tensors. Coupling constants here predicted, as well as rotational constants and molecular dipole moments, are applied to aid analyses of experimental microwave spectra. Chirped pulse Fourier transform microwave spectroscopy has been used to rapidly record the rotational spectra of four isotopologues of the title molecule, CClF₂C(O)Cl, namely ³⁵Cl³⁵Cl, ³⁵Cl³⁷Cl, ³⁷Cl³⁵Cl, and ³⁷Cl³⁷Cl. Only the gauche conformer was observed under the experimental conditions. For the four isotopologues a total of 464, 219, 197, and 77 transitions have been recorded, respectively. With the exception of the ³⁷Cl³⁷Cl isotopologue sufficient data was available to determine all Cl quadrupole coupling tensors. Comparisons between the theoretical and experimental results are made.