Internal rotation in trifluoromethylsulfur pentafluoride: CF3SF5 by Fourier transform microwave spectroscopy

Trifluoromethylsulfur pentafluoride CF 3 SF 5 , which has been attracting much attention because of its unusually large global warming potential, was investigated by Fourier transform microwave spectroscopy in order to determine the twelve-fold potential barrier to internal rotation in this molecule. We have found the V 12 value to be close to zero. Relaxation among internal-rotation and overall-rotation levels was found inhomogeneous, resulting in distributions quite different from thermal in low-temperature molecular beam, which might affect significantly thermodynamic properties of the molecule. Rotational spectra of the 13 C species and the 34 S species were also observed in natural abundance, leading to the r s C S bond length of 1.8808 (7) A.