IR-SPECTRA, RELATIVE STABILITY AND ANGULAR GEOMETRY OF VINYL CHLORIDE-HCL, VINYL BROMIDE-HCL AND ALLYL CHLORIDE-HCL VAN-DER-WAALS COMPLEXESOBSERVED IN LIQUEFIED ARGON

The mid-IR spectra (4000-400 cm(-1)) of vinyl chloride-HCl, vinyl brom ide-HCl and allyl chloride-HCl mixtures, dissolved in liquefied argon at 105 K, have been examined. In all spectra, evidence was found for t he existence of a 1:1 van der Waals complex. At higher concentrations of hydrogen chloride, in the spectra of the vinyl chloride-HCl mixture s, absorption bands of a 1:2 species were also observed. Using spectra recorded at several temperatures between 95 and 120 K, the complexati on enthalpies of CH2=CHCl . HCl and CH2=CHCl .(HCl), were determined t o be -6.5+/-0.2 kJ mol(-1) and -10.6+/-0.3 kJ mol(-1), respectively. A structural study, using ab initio calculations at the MP2/6-31 + G* level, indicates that the complexation between vinyl chloride and HCl can occur either via the chlorine atom or via the K-bond. From a compa rison of the experimental with the ab initio vibrational frequencies i t was concluded that all observed bands of the 1 :I complex are due to a species complexed via the chlorine atom. A similar conclusion appli es to the vinyl bromide and allyl chloride complexes.