Inelastic insights for molecular tunneling pathways: bypassing the terminal groups

As an example of the use of inelastic transport to deduce structure in molecular transport junctions, we compute the orientation dependence of the Inelastic Electron Tunneling (IET) spectrum of the 1-pentane monothiolate. We find that upon increasing the tilting angle of the molecule with respect to the normal to the electrode the spectrum changes as the intensity of some vibrations is enhanced. These differences occur because for higher tilting angles the tunneling path that bypasses the terminal group grows in importance. IETS can therefore be used to establish the molecular orientation in junctions terminating with alkyl chains and to investigate experimentally the relative importance of the available tunneling paths.