Microscopic Molecular Diffusion Enhanced by Adsorbate Interactions

The diffusion of carbon monoxide molecules on the (110) surface of copper was inves-tigated in the temperature range between 42 and 53 kelvin. The activation energy forthermal motion was determined directly by imaging individual molecular displacementswith a scanning tunneling microscope. An attractive interaction between carbon mon-oxide molecules gave rise to the formation of dimers and longer chains. Carbon mon-oxide chains diffused substantially faster than isolated molecules although the chainsmoved by a sequence of single-molecule jumps. A higher preexponential factor in theArrhenius law was found to be responsible for the observed efficiency of chain hopping