The high-frequency rotational spectrum of 1,1,1-trichloroethane and the observation of K=3 splitting

Measurements of the rotational spectrum of 1,1,1-trichloroethane, CH3CCl3, were made up to 678 GHz, J '' = 143, and K = 75, and accurate values for sextic-level spectroscopic constants were determined. Lamb-dip millimeter-wave spectra and sideband FIR-laser spectra were used to observe the K = 3 splitting characterized by the splitting constant h(3) = 1.54(15) X 10(-11) MHz. The present determination and several other recent determinations of h(3) for axially substituted pyramidal molecules allow further empirical rules to be derived regarding the magnitude of h(3) splitting constants in symmetric top molecules. (C) 1995 Academic Press, Inc.