tfarrar

Our research group is interested in the molecular structure and dynamics of liquids. We are especially interested in hydrogen bonded liquids and the forces that drive molecular self-assembly of such liquids. It is now quite clear that simple alcohols and alcohol-water binary solutions form supramolecular structures. There are still questions, however, about the size, shape, dynamics and the lifetimes of these supramolecular structures.

To study these systems we use a variety of experimental and theoretical methods. High resolution nuclear magnetic resonance (NMR) and NMR relaxation time studies provide a wealth of information about molecular size, molecular shape and molecular dynamics. Infrared studies complement the information available from the NMR studies. We have recently developed new experimental/theoretical methods for the accurate measurement of nuclear quadrupole coupling constants (qcc) in the liquid state. This makes it now possible to obtain accurate values for rotational correlation times of nuclei such as deuterium, nitrogen and oxygen. This experimental data for the rotational correlation times of several molecular vectors in a molecule provides important information about the molecular dynamics. It also provides important bench mark information that is important for the testing of the validity of the force fields used in molecular dynamics (MD) simulations. The combination of the Gaussian 98 suite of theoretical programs, molecular dynamics simulations, experimental NMR and infrared experiments is providing new insights about the structure and dynamics of liquids. For example, experimental data and theoretical calculations provide powerful evidence that liquid ethanol consists primarily of cyclic hexamers with an average lifetime at room temperature of about 10 picoseconds. At low temperatures the population of the cyclic hexamers increases significantly and the lifetimes increase by several orders of magnitude. The azeotropic mixture of ethanol and water (80 mole percent ethanol and 20 mole percent water) consists of cyclic pentamers composed of four ethanol molecules and one water molecule. This structure seems to be especially stable and long lived. Work under way includes further work on neat alcohols and ethanol-water binary mixtures. Studies of water, urea and formamide along with binary mixtures of these molecules are also in progress.