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

Infrared and Raman spectra of 1,2-difluoro-1,1,2-trichloroethane (DFTCE) we re measured in the gaseous, liquid and glassy states within a wide temperat ure 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 exis ted as a mixture of three conformers, the most stable having trans-position of C-Cl bonds. Enthalpy differences between conformers in the gaseous phas e were determined to be 1.93 +/- 0.25 (t - g(+)), 0.75 +/- 0.20 (t - g(-)) and 1.09 +/- 0.20 (g(-) - g(+)) kJ mol(-1). The potential function of inter nal rotation (PFIR) was estimated from the torsion fundamentals and calcula ted at the HF/6-31G* and B3LYP/6-31G* levels of theory. (C) 2000 Elsevier S cience B.V. All rights reserved.