Solute-solvent interactions in cryosolutions: a study of halothane-ammonia complexes

Abstract

The formation of C-H center dot center dot center dot N bonded complexes of halothane with ammonia has been studied using infrared and Raman spectroscopy of solutions in the liquid rare gases argon, krypton and xenon, of supersonic jet expansions and of room temperature vapor phase mixtures. For the solutions and for the vapor phase experiments, the formation of complexes with 1 : 1 and 1 : 2 stoichiometry was observed. The complexation enthalpy for the 1 : 1 complex was determined to be -20 (1) kJ mol(-1) in the vapor phase, -17.0 (5) kJ mol(-1) in liquid xenon and -17.3 (6) kJ mol(-1) in liquid krypton. For the 1 : 2 complex in liquid xenon, the complexation enthalpy was determined to be -31.5 (12) kJ mol(-1). Using the complexation enthalpies for the vapor phase and for the solutions in liquid xenon and krypton, a critical assessment is made of the Monte Carlo Free Energy Perturbation approach to model solvent influences on the thermodynamical properties of the cryosolutions. The influences of temperature and solvent on the complexation shifts of the halothane C-H stretching mode are discussed.