The results of inelastic neutron scattering (INS) and molecular dynamics investigations of the vibrational and torsional behavior of monolayer films of Imidazole (Im), N2C3H4, adsorbed on the basal plane of graphite (Gr) (6 fold symmetry and semiconductor) and the (100) plane of MgO (4-fold symmetry and an ionic insulator) will be presented. Our interest in Im, a polar ring molecule derives from the fact that it serves as a prototype for more complicated systems of particular interest in chemistry and biology, where it is considered a model component to study proton conductivity and hydrogen bonding in such areas as nucleic acid bases, amino acids, electrolytes and photo voltaics. The underlying purpose of these neutron scattering investigations is to understand how the adsorption of Im on these surfaces affects the physical and chemical properties of the molecule and that of the adsorbing material. These monolayer films can be considered a two-dimensional (2D) system where questions of fundamental importance can be addressed. We have performed a series of MD simulations on the adsorption of ring molecules on the basal plane of Gr and the MgO(100) surface. We aim to understand how the observed changes in the rotational and translational diffusion as well as the internal torsional, vibrational and librational modes and collective phonon modes depend upon whether adsorption of Im takes place on the 4-fold versus the 6-fold symmetry and composition/periodicity of these materials. Preliminary MD results for Im on Gr and MgO will be presented. We use these simulations to examine the temporal behavior of the system and then use the modeling results to more fully understand the INS investigations. In the Im/Gr case a jump diffusion process with a tendency for the molecules to hop between adsorption sites on Gr with a floating solid at lower temperatures is observed. On the other hand, the diffusion of Im on MgO appears to be ergodic and more inclined to be in a single flexible line like a piece of spaghetti. The implications of these results will be discussed.<br/>

Adsorption of monolayer films of imidazole on MgO (100) and graphite: A neutron scattering and molecular modeling investigation

256th National Meeting (2018)

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