College Park, Maryland      June 6 - 10 , 2004

M4-C6 (5:15 PM): Structure and dynamics of oligomer molecules within monolayer films on graphite

E.J. Kintzel, Jr., K.W. Herwig (Spallation Neutron Source, Oak Ridge National Laboratory), I. Peral (NIST Center for Neutron Research; Department of Materials Science and Engineering, University of Maryland)

The structure and dynamics of monolayer films of the aromatic molecules o-terphenyl (o-3P), p-terphenyl (p-3P), p-quaterphenyl (p-4P), and p-sexiphenyl (p-6P) adsorbed onto the surface of graphite has been carried out using elastic and quasielastic neutron scattering. Structural results of the p-phenylene oligomer (p-nP) films indicate an orientation consistent with the long molecular axis parallel to the graphite surface. Initial dynamic results indicate a phase change within the p-nP films at approximately 300-325 K. At temperatures below 325 K, the scattering is consistent with reorientation of the phenyl rings around the long molecular axis. At temperatures above 300 K, the scattering is much stronger and appears at lower momentum transfers, indicating some form of translational motion in combination with reorientation of the phenyl rings. Monolayer o-3P films exhibit molecular motions consistent with both reorientations of the phenyl rings as well as translations at temperatures as low as 190 K. There is no abrupt change in the character of the dynamics for the o-3P films.

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