VIBRATIONAL ANALYSIS OF THE VAN-DER-WAALS COMPLEXES BETWEEN VINYL FLUORIDE AND HYDROGEN-CHLORIDE IN LIQUEFIED ARGON

The mid-infrared spectra (4000-400 cm(-1)) of vinyl fluoride/HCl and v inyl fluoride/DCl mixtures, dissolved in liquefied argon at 105 K, wer e examined. In both cases, evidence was found for the occurrence of a 1:1 van der Waals complex between CH2 = CHF and HCl (DCl). At higher c oncentrations of hydrogen chloride, absorption bands of a 1:2 species were also observed. By using spectra recorded at several temperatures between 95 and 115 K, the complexation enthalpies of CH2 = CHF . HCl a nd CH2 = CHF .(HCl)2 were determined to be -5.78 +/- 0.13 and -9.85 +/ - 0.34 kJ mol(-1), respectively. A structural study, using nb initio c alculations at the MP2/6-31 + G* level, indicates that the complexati on can occur either via the fluorine atom or via the pi bond. From a c omparison of the experimental with the ab initio vibrational frequenci es, it was concluded that all observed bands of the 1:1 complex are du e to a species complexed via the fluorine atom.