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Adamantane <I>C₁₀H₁₆</I> is an interesting archetypal plastic crystal which has been extensively studied. It undergoes transition from a low temperature ordered phase to a high temperature disordered phase at T=208.6K. The <I>C₁₀H₁₆</I> molecule has tetrahedral symmetry and the orientational disorder to the plastic phase has been interpreted in terms of the distribution of the molecules between two equally preferred orientations. A molecular dynamics simulation of <I>C₁₀H₁₆</I> has been carried out using the CCP5 Library program <I>moliq-dynamo</I>, written by Dr. D Fincham of Keele University. The simulation model consists of rigid molecules interacting with an atom-atom pairwise additive potential. The dynamics of the adamantane molecules in the plastic phase have been investigated and results have been compared with previous work. The molecular trajectories generated by the simulation have been used to evaluate the intensity of diffuse x-ray scattering from the crystal. Results have been compared with experimental data obtained from energy-dispersive x-ray scattering measurements made at the Daresbury SRS. Using a series of simplified models of the crystal, the relative contributions to the scattered intensity from translational and orientational disorder have been investigated.

This thesis contains the results of molecular dynamics simulations of molecule-surface interactions, looking particularly at fullerene molecules and carbon surfaces. Energetic impacts of fullerene molecules on graphite create defect craters. The relationship between the parameters of the impacting molecule and the parameters of the crater are examined and found to be a function of the energy and velocity of the impacting molecule. Less energetic fullerene molecules can be scattered from a graphite surface and the partitioning of energy after a scattering event is investigated. It is found that a large fraction of the kinetic energy retained after impact is translational energy, with a small fraction of rotational energy and a number of vibrational modes. At impact energies where the surface is not broken and at normal incidence, surface waves are seen to occur. These waves are used to develop a method of desorbing molecules from a graphite surface without damage to either the surface or the molecules being desorbed. A number of fullerene molecules are investigated and ways to increase the desorption yield are examined. It is found that this is a successful technique for desorbing large numbers of intact molecules from graphite. This technique could be used for desorbing intact molecules into a gas phase for mass spectrometric analysis.

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