Iryna D. Nanoscale clusters in hydrogen-bonded molecular liquids

The problem of molecular associates forming in liquids with intermolecular hydrogen bonds was investigated by methods of vibrational spectroscopy and quantum-chemical simulation. Spectroscopic manifestations of clustering processes in homologous series of monohydric alcohols from methanol to decanol as well as in tertial alcohol tert-butanol were investigated. Individual molecules and small alcohol clusters were isolated in low-temperature argon and nitrogen matrices. Their infrared spectra were registered during gradual heating of the matrix. These experiments allowed constructing an experimental model of the structure transformations in alcohols during the phase transition from gas to liquid. Quantum-chemical calculations of optimal geometries and corresponding vibrational spectra of different alcohol clusters were carried out in the approximation B3LYP/6-31G (d, p). The cluster compositions of the investigated samples at different temperatures were determined. It was shown that the transformation of cluster structure in alcohols occurs gradually from small clusters to bigger ones. The analysis of the bandwidths of the registered absorption bands was carried out. It was shown that the broadening of the spectral bands with temperature increasing is related to the increasing of cluster sizes in the sample, the growing of their conformational variety and shortening of the lifetime of hydrogen-bonded clusters. The effects of isolating matrix material on the peculiarities of the clustering process in the isolated substance were determined. It was shown that in the alcohols with longer alkyl chains (beginning from octanol), where the steric repulsion plays an important role and competes with hydrogen bonding, the relative number of chain structures and monomers increases.