On the formation of a van der Waals complex between ethene and carbon dioxide in liquid argon. An FTIR and ab initio study

The mid-infrared spectra of mixtures of ethene and carbon dioxide dissolved in liquid argon have been investigated between 88 and 123 K. At higher concentrations of ethene, evidence was found for the formation of a 1:1 complex in which the carbon atom of the CO2 moiety binds to the CyC double bond. By recording spectra at different temperatures, the complexation enthalpy for the 1:1 complex was determined to be 24.9(1) kJ mol21. Using Free Energy Perturbation Monte Carlo simulations to correct for solvent influences and statistical thermodynamics to account for zero-point vibrational and thermal influences, the complexation enthalpy was transformed into a vapor phase complexation energy. The resulting value, 26.8(8) kJ mol21, is compared with theoretical data obtained from ab initio calculations in which the equilibrium geometry of the complex is calculated using BSSE-corrected gradient techniques. q 2004 Published by Elsevier B.V.