Collective Excitations in Ethane Monolayers Adsorbed on Graphite (0001) Surfaces

Abstract

Inelastic incoherent neutron spectra below 4.1 THz have been obtained for the $\sqrt{3}\ifmmode\times\else\texttimes\fi{}4$ "herringbone" and $\sqrt{3}\ifmmode\times\else\texttimes\fi{}\sqrt{3}$ "on-end" monolayer phases of ethane adsorbed on graphite basal planes. One-phonon cross sections calculated independently with empirical atom-atom potentials make possible identification of the collective vibrational modes observed and reproduce qualitatively the rather different spectra of the two phases.