Non-ideality of binary mixtures Water[ndash ]methanol and water[ndash ]acetonitrile from the viewpoint of clustering structure

Water–methanol and water–acetonitrile, which show exothermic and endothermic mixing, respectively, represent good contrast in non-ideality of a binary mixture. The microscopic structure observed through the mass-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 acetonitrile 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 disintegrated in the presence of water. Such findings could partially explain the non-ideality of these binary mixtures on the basis of the cluster structures.