Abstract

In this work we aim to understand the microscopical mechanisms of diffusion and friction of benzene molecules on graphite surfaces – a simple model system that shows, nevertheless, a wealth of phenomena that depend on, e.g., coverage and temperature [1]. Quasi-elastic neutron scattering (QENS) spectroscopy yields novel insights in the diffusive behavior of benzene, C6H6 , adsorbed on the basal plane [0001] of graphitic substrates. Our extensive study of the diffusion for a wide range of coverages, from 0.1 to 1.0 monolayers (ML), and temperatures, from 60K to 140K, reveals that intermolecular interactions play an essential role in the surface dynamics of molecules. The rough binary collision model [2,3] between adsorbates provides values for the friction parameters in agreement with the experimental results, indicating that molecules behave as hard disks and that a significant part of the origin of friction lies in the exchange of linear and angular momentum between them through binary collisions.

[1] H. Hedgeland et al., Nature Physics 5 (2009) 561 – 564

[2,3] D. Chandler, J. Chem. Phys. 60, 3500 (1974); D. Chandler, J. Chem. Phys. 60, 3508 (1974).