8th Liquid Matter Conference September 6-10, 2011 Wien, Austria ...

Tue 611:23-14:00P2.73The structure of simple aromatic liquids and solutions byneutron scatteringNeal Skipper, 1 Tom Headen, 2 Chris Howard, 3 Daniel Bowron, 4 and Alan Soper 41 University College London, Gower Street, WC1E 6BT, London, United Kingdom2 Cella Energy, Didcot, United Kingdom3 London Centre for Nanotechnology, London, United Kingdom4 ISIS Facility, Didcot, United KingdomHigh-resolution neutron diffraction has been used in conjunction with hydrogen/deuterium isotopiclabeling to determine with the structure of two archetypal aromatic liquids (benzene and toluene)and also solutions of pyrene in benzene and phenol in water. We discover the nature of aromatic π-π interactions in the liquid state by constructing for the first time a full six-dimensional spatial andorientational picture of these systems. In aromatic solvents and solutions we find that superficiallythe first neighbor shells appear isotropic, but our multidimensional analysis shows that the localorientational order in these liquids is much more complex. At small molecular separations (< 5Å) there is a preference for parallel π-π contacts in which the molecules are offset to mimic theinterlayer structure of graphite. At larger separations (> 5 Å) the neighboring aromatic rings arepredominantly perpendicular, with two H atoms per molecule directed toward the acceptor’s πorbitals. The so-called ”anti-hydrogen-bond” configuration, proposed as the global minimum forthe benzene dimer, occurs only as a saddle point in our data. The observed liquid structures aretherefore fundamentally different than those deduced from the molecular dimer energy surfaces.We will present also data for solutions of phenol in water, in which we find that the aromatic soluteshave a propensity to form ortho-parallel π-π contacts, with water forming weak hydrogen bondsto the delocalised electron cloud.73