NONIDEALITY OF BINARY-MIXTURES - WATER-METHANOL AND WATER-ACETONITRILE FROM THE VIEWPOINT OF CLUSTERING STRUCTURE

Water-methanol and water-acetonitrile, which show exothermic and endot hermic mixing, respectively, represent good contrast in non-ideality o f a binary mixture. The microscopic structure observed through the mas s-spectrometric analysis of clusters isolated from solution also shows good contrast between these binary mixtures as follows: (1) methanol molecules have substitutional interaction with water clusters, while a cetonitrile molecules have additional interaction with water clusters; (2) the clustering of methanol molecules are promoted in the presence of water; on the contrary, the acetonitrile clusters are disintegrate d in the presence of water. Such findings could partially explain the non-ideality of these binary mixtures on the basis of the cluster stru ctures.