STRUCTURE OF CLUSTERS IN ETHANOL-WATER BINARY-SOLUTIONS STUDIED BY MASS-SPECTROMETRY AND X-RAY-DIFFRACTION

The structure of clusters in ethanol-water binary solutions at x(E) (e thanol mole fraction) greater than or equal to 0.2 was investigated by the mass-spectrometric analysis of clusters isolated from liquid drop lets and X-ray diffraction measurements of the intact solution. The av erage number of water molecules (N-a) of the ethanol m-mer hydrates (5 < m < 15) in the mixtures at 0.2 less than or equal to x(E) less than or equal to 0.8 was found to be expressed by a function of the water mole fraction (x(w)), N-a = {(m/4.2)-1}(2) (x(w)+0.85), suggesting tha t the fundamental structure of ethanol polymer-hydrates is invariable in this region. An inflection point of N-a was found at x(E) approxima te to 0.2. The radial distribution functions (RDFs) from X-ray measure ments demonstrated a decrease of linear hydrogen bonds at 2.8 Angstrom with increasing x(E), while keeping the strongest peak at 4.8 Angstro m for 0.4 less than or equal to x(E) less than or equal to 1.0. On the basis of a composition analysis of the mass spectra and the concentra tion dependence of RDFs, we propose the most likely model of ethanol-w ater binary clusters formed in the region 0.2 less than or equal to x( E) less than or equal to 0.8.