PROTON SOLVATION IN TERNARY CLUSTERS OF WATER-METHANOL ACETONITRILE - EVIDENCE FOR CYCLIC STRUCTURES

The distributions of protonated ternary clusters containing water (W), methanol (M) and acetonitrile (A) have been studied as a function of composition using EI ionization of the ternary cluster beam. The cluster distributions show enhanced ion intensities for the sequence H+WnMmAn+2 indicating solvent shell's closing by the blocking groups of acetonitrile molecules. Evidences for cyclic structures in ternary clusters containing five methanol or four water molecules are presented. Cyclic structures in water clusters containing 4-8 molecules are proposed. Implications of the cluster data to the structure of bulk liquid mixtures is discussed. In particular, the cluster model for water-acetonitrile is consistent with the concept of ''microheterogeneity'' observed in water-acetonitrile liquid mixtures.