In this project in the Physical Chemistry Program of the Chemistry Division, Prof. T. S. Zwier of Purdue University will investigate the properties of gas-phase solute-solvent clusters by resonant ion-dip infrared spectroscopy and fluorescence-dip infrared spectroscopy. These studies concern the solvent structure in complexes involving aromatic molecules, conformers of biomolecules, and intramolecular H-atom tunneling. Among the several systems to be investigated are those of water, methyl alcohol, chloroform, hydrogen chloride, methane, and acetylene as the solvent species for benzene. Additional studies focus on the conformations of aromatic amino acids, their analogs, and their solvent-containing clusters, and on tropolone and several of its derivatives in which the H-atom tunneling reactions of the intramolecularly hydrogen-bonded hydrogen atoms play a role. Weak intramolecular and intermolecular interactions that involve a hydrogen atom are known as hydrogen-bonding forces. These play a significant role in defining the shape and conformation of especially large biomolecules and the association of molecules into cluster aggregates. Gas phase clusters provide an important testing ground for theories aimed at understanding the hydrogen bond and its consequences. The importance and complexity of water and the alcohols has prompted much experimental and theoretical work on their gas phase clusters. Experimental data on the variations of cluster properties with cluster size are sparse and are needed to test theoretical models. In the condensed phase the interaction between solute and solvent must consider both the disruption of the solvent's structure imposed by the solute molecule and site-specific attractions and repulsions between solvent and solute molecules. The present research will serve to obtain a better understanding of these problems in physical chemistry.
