Rotational isomerism in 1,2-difluoro-1,1,2-trichloro-ethane as studied by vibrational spectroscopy and ab initio calculations

Abstract

Infrared and Raman spectra of 1,2-difluoro-1,1,2-trichloroethane (DFTCE) were measured in the gaseous, liquid and glassy states within a wide temperature interval. The complete assignment of the spectra was made on the basis of experimental information and theoretical (ab initio and DFT) force field calculations. It was found that in all aggregate states the substance existed as a mixture of three conformers, the most stable having trans-position of C–Cl bonds. Enthalpy differences between conformers in the gaseous phase were determined to be 1.93±0.25(t−g+),0.75±0.20(t−g−) and 1.09±0.20(g−−g+)kJmol−1. The potential function of internal rotation (PFIR) was estimated from the torsion fundamentals and calculated at the HF/6-31G∗ and B3LYP/6-31G∗ levels of theory.