Far infrared spectrum, barrier to internal rotation, and ab initio calculations for 3,3,3-trifluoropropene

Abstract The far infrared spectrum of gaseous 3,3,3-trifluoropropene, CH 2 CHCF 3 , between 350 and 30 cm −1 has been recorded at a resolution of 0.10 cm −1 . The torsional fundamental for the CF 3 rotor is observed at 83.52 cm −1 . There are three and possibly four “hot bands”, which accompany this fundamental falling to lower wavenumbers with decreasing intensities. Utilizing these torsional data along with structural parameters obtained from MP2/6-311+G** ab initio calculations to calculate the kinetic constant F , the barrier to internal rotation has been determined to be 630±10 cm −1 (7.54±0.12 kJ/mol) and the V 6 term is relatively small with a value of −30±5 cm −1 (−0.36±0.06 kJ/mol). These results are compared to the CH 3 barrier of propene as well as to those of several CF 3 rotors. The harmonic force fields, infrared intensities, Raman activities, and depolarization ratios have been obtained from both ab initio RHF/6-31G* and MP2/6-31G* calculations and the results compared. Additionally, predicted quantities are compared to the corresponding experimental values when appropriate as well as with some corresponding results for some similar molecules.