Reassignment of the vibrational spectra of CHF2CH3 (HFC-152a), CF3CH3 (HFC-143a), CF3CHF2 (HFC-125), and CHCl2CF3 (HCFC-123).

We provide new or revised vibrational assignments for three hydrofluorocarbons (HFCs) and one hydrochlorofluorocarbon (HCFC) through the combined use of experimental absolute infrared intensity measurements, experimental Raman measurements and ab initio computations of vibrational frequencies, absolute infrared intensities, and Raman intensities. CHF2CH3 (HFC-152a), CF3CH3 (HFC-143a), CF3CHF2 (HFC-125), and CHCl2CF3 (HCFC-123) are the molecules investigated in this study. We have measured the vapor infrared spectra from 400 to 4000 cm_1 at a resolution (0.08 cm_1) sufficient to resolve some overlapping fundamentals and to assign symmetry species for several bands on the basis of their rotational band contours and absolute infrared intensities. Raman spectra were measured for the HFCs at pressures between 3.8 and 11.1 atm and for HCFC-123 in the liquid phase. Second-order Moller-Plessett (MP2) level of theory and the 6-31G** basis set were used to optimize molecular geometry and calculate harmonic vibrational frequencies and infrared intensities; Hartree Fock (HF) level of theory was used to calculate Raman intensities. The higher-resolution infrared spectra and experimental absolute infrared intensities, the Raman spectra and relative Raman intensities, together with the results of the computations, allow afirm assignment of previously ambiguous bands. On the basis of the current assignments, we find that the scaled MP2:6-31G** frequencies are in good agreement with the observed frequencies. Furthermore, the calculated absolute infrared intensities and calculated Raman intensities are generally in good agreement with the experimental measurements.

Main Author: Tai, Stephanie.
Other Authors: Papasavva, Stella., Kenny, Jonathan., Gilbert, Brian., Janni, James., Steinfeld, Jeffrey., Taylor, Joshua., Weinstein, Randy.
Language: English
Published: 1998
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