Tunneling dynamics of a hydroxyl group adsorbed on Cu(110)

Dynamics of a hydroxyl (OH) group and its dimer adsorbed on Cu(110) is investigated at 6 K with a scanning tunneling microscope (STM). For the monomer, the inclined OH axis switches back and forth between the two equivalent orientations via hydrogen-atom tunneling. The motion is enhanced by tunneling electron that excites the OH bending mode that directly correlates with the reaction coordinate. The inelastic electron-tunneling spectra exhibit either peak or dip, depending on the position of the STM tip over the molecule. The switch motion is quenched for the hydroxyl dimer since it is stabilized by hydrogen-bond formation, whereas it is induced by inelastic excitation of the OH stretch mode.