Chlorine Nuclear Quadrupole Coupling in Chlorodifluoroacetyl Chloride: Theory and Experiment

A potential energy scan of chlorodifluoroacetyl chloride, CF ₂ Cl-C(=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 ³⁵ Cl and ³⁷ Cl 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. CClF ₂ C(=O)Cl, namely ³⁵ Cl- ³⁵ Cl, ³⁵ Cl- ³⁷ Cl, ³⁷ Cl- ³⁵ Cl, and ³⁷ Cl- ³⁷ Cl. 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 ³⁷ Cl- ³⁷ Cl isotopologue sufficient data was available to determine all Cl quadrupole coupling tensors. Comparisons between the theoretical and experimental results are made.