The diffusion of COT on Cu(111) observed in the angstrom-picosecond window

Avidor1, I. Calvo-Almazan1, J.A. Lau1, P.S.M. Townsend1, D.J. Ward1, J. Ellis1, W. Allison1 and B.J. Hinch2

1.Cavendish Laboratory, University of Cambridge, JJ Thomson Ave, Cambridge, CB3 0HE, United Kingdom – Cambridge (United kingdom)

2.Department of Chemistry and Chemical Biology, Rutgers University, Piscataway, New Jersey 08854, USA

Recent developments in scattering experiments have allowed motion on a molecular scale to be explored in the pico- to nano- second timescales, using ‚Äč3He Spin Echo spectroscopy[1,2]. We have applied the method to study the mobility of 1,3,5,7-cyclooctatetraene (COT,C8H8) on Cu(111). We have measured the dynamics both at low coverage (isolated molecules) and at a medium coverage of 0.3ML, at temperatures of 200K-450K. The diffusive translational motion of COT proceeds by jump diffusion over a Bravais lattice of preferred adsorption sites, with a short residence time of 2[ps] and a low energy barrier of ~30[meV]. In addition, we see evidence for fast diffusion which we relate to rotational motion, and intermolecular interactions between adsorbates. A weakly dispersive vibrational mode at ~1[meV] is seen over a narrow window of parallel momentum transfer.

[1] G. Alexandrowicz et. al. Progress in Surface Science, 84(11), 2009.

[2] AP Jardine et. al. Journal of Physics: Condensed Matter, 19(30), 2007.