THE MICROWAVE-SPECTRUM AND OH INTERNAL-ROTATION DYNAMICS OF GAUCHE-2,2,2-TRIFLUOROETHANOL

The microwave spectra of CF3CH2OH and CF3CH2OD have been investigated from 5 to 26 GHz with a pulsed-nozzle Fourier-transform microwave spec trometer and from 26 to 42 GHz with an electric resonance optothermal spectrometer. Tunneling of the OH proton between the two isoenergetic gauche conformations splits the observed transitions into two tunnelin g components. An effective rotation-tunneling Hamiltonian is used to f it the a- and b-type pure rotational and c-type torsional-rotational t ransitions for both isotopomers to better than 5 and 13 kHz for the OH and OD forms, respectively. The tunneling splittings determined from the fits for the OH and OD isotopomers are 5868.6952(16) and 208.5037( 42) MHz, respectively. A structural analysis using the moments of iner tia of the OH and OD isotopomers determines that the hydroxyl hydrogen is directed toward the fluorine with a F ... H separation of 2.561(1) Angstrom and a dihedral angle of phi(CCOH) = 68.97(6)degrees. The obs erved tunneling splittings are fit to a double-minimum potential, givi ng gauche-gauche tunneling barriers of 763 and 720 cm(-1) and OH torsi onal fundamental frequencies of 364 and 271 cm(-1) for CF3CH2OH and CF 3CH2OD, respectively. The uncertainties shown in parentheses throughou t the paper are one standard deviation. (C) 1995 American Institute of Physics.