AB-INITIO VIBRATIONAL FREQUENCIES OF THE TRIFLIC ACID MOLECULE

The optimized geometry, harmonic vibrational frequencies, and infrared intensities of the trifluoromethanesulfonic (triflic) acid, CF3SO2OH, have been determined by ab initio self-consistent Hartree-Fock calculations and second-order Moller-Plesset perturbation theory with 6-31G** and lower basis sets. The optimized geometry of the triflic acid molecule is in good agreement with that reported from electron diffraction experiments. The overall symmetry for the molecule, however, is C1, and not C(s) as suggested from the experiments. The symmetric CF3 and SO2 stretching vibrational modes of the triflic acid are seen to be reversed compared to the assignment from the infrared spectra, reported earlier in the literature. The CF3 stretchings and the O=S=O bending normal modes include strong couplings of different internal coordinates. The vibrational frequencies and the infrared intensities are sensitive to the basis set choice as well as to electron correlation effects.