Rotation-tunneling spectra and barriers of isotopologues of 2,2,2-trifluoroethanol and 2,2,3,3,3-pentafluoropropanol

Abstract

Rotation-tunneling spectra of two common fluoroalcohols, i.e., 2,2,2-trifluoroethanol (TFE) and 2,2,3,3,3-pentafluoropropanol (PFP), were recorded using two chirped pulse Fourier transform microwave spectrometers in the 2–6 and 8–12 GHz ranges. Rotation-tunneling spectra of two monosubstituted 13C isotopologues of TFE and the OD isotopologue of PFPwere assigned and fitted for the first time. The torsional potential energy scan and transition state calculations were performed at the B3LYP-D3BJ/def2-TZVPPD level to obtain the theoretical tunneling barriers for the parent, 13C and D isotopologues. The associated tunneling splittings were predicted based on several semi-empirical tunneling models and compared directly to the experimentally observed values to evaluate the performance of the models and the theoretical tunneling barriers. For the previously unassigned rotation-tunneling spectrum of the Tg conformer of PFP which is deuterated at the hydroxy group, PFPTg(OD), we applied the same procedure to predict the tunneling splitting. Furthermore, several scaling procedures were tested and the tunneling splitting predicted offered great help in finally assigning the rotation-tunneling spectrum of PFPTg(OD).