Microwave Spectrum, Barrier to Internal Rotation, and Quadrupole Coupling of Acetyl Bromide

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Abstract
The microwave spectra of the two acetyl bromide species, CH3COBr79 and CH3COBr81, have been investigated in the region 12 000 to 33 000 Mc. The bromine nuclear quadrupole hyperfine splittings were analyzed to give values for the quadrupole coupling constants. The observed coupling constants indicate a considerable deviation from cylindrical symmetry of the electric field gradient about the C–Br bond. Several of the rotational transitions were further split into doublets due to the hindered internal rotation of the methyl group. The quadrupole hyperfine and internal rotation splittings were found to be essentially independent, and analysis of the latter gives a barrier to internal rotation of 1305±30 cal/mole.