Trifluoroacetic acid (TFA, CF3COOH) is the final degradation product of many hydrochlorofluorocarbons, hydrofluorocarbons, and hydrofluoroolifines in the troposphere. The CF3 internal rotor is a heavy C3v top that strongly couples with the overall rotation of the molecule (ρ = 0.68). Despite the low torsional barrier of about 230 cm^-1, the high mass of the top leads to low tunneling probability in the ground state. The A-E splitting is not observable in the ground state rotational spectrum even using  molecular beam Fourier transform microwave spectroscopy which typical resolution is few kHz^[1]. In previous studies, the splitting was observed only for the v_t=4 excited torsional state^[2], whereas the rotational lines for the v_t=1-3 states were not well measured. The missing lines from the v_t=1-3 states lead to the question of what the exact torsional barrier is, and in which state the tunneling splitting becomes observable. We perform a new global analysis of the TFA v_t=0-4 states with new spectral measurements from 50 to 330 GHz, and from 1.2 to 1.5 THz. In our data set, the tunneling splitting is observed for v_t=4 lines, and a small portion of v_t=3 lines. Our analysis was performed using the rho-axis method and RAM36 code. This joint analysis of five torsional states resulted in accurate determination of the V3 and V6 potential energy terms. The latest results will be presented.

[1] Antolinez, S., Alonso, J., Dreizler, H. and Sutter, D., Zeitschrift für Naturforschung A, 1999, 54, 524-538.

[2] Stolwijk, W. M. and van Eijck, B. P., Journal of Molecular Spectroscopy, 1985, 113, 196-207.