The van der Waals molecules of carbonyl sulfide with hydrogen chloride and boron trifluoride - An infrared study in cryosolution

Ab initio calculations at the MP2/6-31 + G** level show that OCS can form two isomeric 1:1 complexes with HCl and with BF3. For both Lewis acids, in the more stable isomer the van der Waals bond occurs via the oxygen atom of OCS, in the less stable isomer via the sulfur atom. Mixtures of OCS with either HCl or BF3, disolved in liquid argon, have been investigated between 98 and 117 K, using mid-infrared spectroscopy. In both cases the formation of a complex was observed. The complexation enthalpies, determined from a temperature dependent study, are -4.0(3) kJ mol(-1) for OCS . HCl and -8.0(5) kJ mol(-1) for OCS BF3. Comparison with the ab initio vibrational frequencies of the species involved shows that in both cases OCS complexes via the oxygen atom. Tn neither case have bands due to a second isomer of the complex been found. (C) 1998 Elsevier Science B.V.