INDUCING AND VIEWING THE ROTATIONAL MOTION OF A SINGLE-MOLECULE

Tunneling electrons from the tip of a scanning tunneling microscope we re used to induce and monitor the reversible rotation of single molecu les of molecular oxygen among three equivalent orientations on the pla tinum(111) surface. Detailed studies of the rotation rates indicate a crossover from a single-electron process to a multielectron process be low a threshold tunneling voltage. Values for the energy barrier to ro tation and the vibrational relaxation rate of the molecule were obtain ed by comparing the experimental data with a theoretical model. The ab ility to induce the controlled motion of single molecules enhances our understanding of basic chemical processes on surfaces and may lead to useful single-molecule devices.