Microwave Spectrum of Acetyl Iodide

The microwave spectra of CH3COI and CD3COI were investigated in the region 8000 to 27 000 Mc/sec. The effects of internal rotation and quadrupole perturbations were found to be essentially independent. The height of the potential barrier hindering the methyl group internal rotation was determined to be 1301±30 cal/mole from measured CH3COI doublet splittings. Level mixing was found for several pairs of rotational states, analogous to Fermi resonance in vibrational levels. Mixing effects permitted determination of the quadrupole coupling constant χab in both isotopic species. The values for quadrupole coupling constants in CH3COI are χaa=−1563±2, χbb=914±2, and χab=−135.6±2 Mc/sec. In CD3COI the values are χaa=−1541±3, χbb=892±2, and χab=−258.5±10 Mc/sec. Diagonalization of each of the above tensors gives χαα=−1569 and χββ=920 Mc/sec.