The microwave spectrum and OH internal rotation dynamics of gauche-2,2,2-trifluoroethanol

Abstract

The microwave spectra of CF3CH2OH and CF3CH2OD have been investigated from 5 to 26 GHz with a pulsed-nozzle Fourier-transform microwave spectrometer 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 tunneling components. An effective rotation-tunneling Hamiltonian is used to fit the aan 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 inertia 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) Å and a dihedral angle of φ(CCOH)=68.97(6)°. The observed tunneling splittings are fit to a double-minimum potential, giving gauche–gauche tunneling barriers of 763 and 720 cm−1 and OH torsional fundamental frequencies of 364 and 271 cm−1 for CF3CH2OH and CF3CH2OD, respectively. The uncertainties shown in parentheses throughout the paper are one standard deviation.