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College Park, Maryland      June 6 - 10 , 2004

MP15: On the structure of liquid hydrogen fluoride

S. E. McLain (The University of Tennessee - Department of Chemistry; Intense Pulsed Neutron Source, Argonne National Lab), C. J. Benmore, J. E. Siewenie (Intense Pulsed Neutron Source, Argonne National Lab), J. F. C. Turner (The University of Tennessee - Department of Chemistry; Neutron Science Constortium)

An experimental determination of the partial structure factors for liquid hydrogen fluoride has been in demand from theorists for more than two decades. However this is not a straightforward task, given the inherent difficulty of sample containment due to the chemically aggressive nature of the material. We present the first experimental determination of the partial structure factors SHH(Q), SHF(Q) and SFF(Q) for liquid hydrogen fluoride at 296 2 K and 1.2 0.2 bar. This was accomplished by using a combination of isotopic substitution in neutron diffraction and high energy x-ray diffraction methods. Experiments were performed in custom built Alloy 400 cells. Despite the dearth of detailed experimental information, the structure of HF in the liquid state has been widely simulated using a variety of inter-atomic potentials, as well as ab initio and quantum mechanical methods. The predictions range from the liquid being comprised of chains to clustering in the liquid state. Experimentally, the structure of the liquid is found to be composed of short, hydrogen-bound chains as evidenced by the hydrogen-fluorine partial correlation function. The results also show strong inter-chain interactions in the fluorine-fluorine partial radial distribution function. Reverse Monte Carlo modeling and coordination number analyses both indicate the existence of long winding chains with very little branching. The neutron diffraction data were collected on the Glass Liquids and Amorphous materials Diffractometer located at Intense Pulsed Neutron Source located and the high energy x-ray diffraction data were collect at the 11-IDC beam line on the BESSRC-CAT at the Advanced Photon Source, both located at Argonne National Laboratory.

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