Microwave Spectrum of Acetic Acid, CH3COOH and CD3COOH

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Abstract
The microwave spectra of two isotopic species of acetic acid, CH3COOH and CD3COOH, have been re‐examined. Using the principal axis method and a computer program extended to include terms through n = 6 in the perturbation series and denominator corrections, 30 new E‐type transitions have been identified. For CH3COOH, an excellent fit of the observed A–E splittings is obtained using the parameters I α = 3.216 ± 0.002 amu ·Å 2 , θ = 4°30′ ± 15′ for the angle between the methyl group axis and the a principal axis, and s = 13.232 ± 0.002 . Assigned splittings are very large (up to 3600 MHz), and the calculated spectrum is sensitive to all three parameters. The value for the barrier to internal rotation of the methyl group is V 3 = 480.8 ± 0.5 cal / mole for CH3COOH, and 468 ± 2 for CD3COOH. Stark effect measurements using four A‐type transitions give the dipole moment components: μ a = 0.86 ± 0.01 D , μ b = 1.47 ± 0.02 D , and μ = 1.70 ± 0.02 D .