Directed Long-Range Migratory Reaction of Benzene on Si(100)

Electron impact on chemisorbed benzene at Si(100) is shown by scanning tunneling microscopy to cause long-range molecular recoil in the plane of the surface, followed by chemisorptive reattachment at a substantial distance (on average, 48 A) from the originating event. Several indicators—directionality of migration, persistance of motion over obstacles, and insignificant probability of desorption—all point to a rolling mechanism in which the recoiling molecule cartwheels across the surface in a physisorbed state. In distinction to our previous report of long-range migration of alkenes on the same surface [Nat. Chem. 2011, 3, 400−408], in the present case, the benzene molecules migrate substantially further and favor motion along the dimer rows rather than across them. Ab initio theory provides a qualitive model that satisfactorily explains these experimental observations.