ROTATIONAL SPECTRA, ELECTRIC-DIPOLE MOMENT AND METHYL-GROUP INTERNAL-ROTATION BARRIER OF 1,1,1-TRIFLUOROPROPANE

The microwave spectra of the main species of 1,1,1-trifluoropropane an d the three singly substituted C-13 isotopic species have been studied in the frequency region 6-40 GHz using Stark modulation and Fourier-t ransform microwave spectroscopy. Accurate rotational spectroscopic con stants and quartic centrifugal distortion constants have been obtained for the ground vibrational state. A reasonable molecular structure ha s been derived from the rotational constants and planar moments of ine rtia. The barrier to internal rotation of the methyl top has been dete rmined from the A-E splittings to be 2635(4) cal mol(-1). The dipole m oment components have been computed from Stark effect measurements to be mu(a) = 2.172(4) D and mu(b) = 1.140(9) D with a total dipole momen t of mu = 2.453(8) D.