Dynamics of surface-migration: Electron-induced reaction of 1,2-dihaloethanes on Si(100)

Scanning Tunneling Microscopy was used to investigate the electron-induced reaction of 1,2-dibromoethane (DBE) and 1,2-dichloroethane (DCE) on Si(100).We observed a long-lived physisorbed molecular state of DBE at 75 K and of DCE at 110 K. As a result we were able to characterize by experiment and also by ab initio theory the dynamics of ethylene production in the electron-induced surface-reaction of these physisorbed species. For both DBE and DCE the ethylene product was observed to migrate across the surface. In the case of DBE the recoil of the ethylene favored the silicon rows, migrating by an average distance of 22 Å, and up to 100 Å. Trajectory calculations were performed for this electron-induced reaction, using an ‘Impulsive Two-State’ model involving an anionic excited state and a neutral ground-potential. The model agreed with experiment in reproducing both migration and desorption of the ethylene product. The computed migration exhibited a ‘ballistic’ launch and subsequent ‘bounces’, thereby accounting for the observed long-range migratory dynamics. [Display omitted] •1,2-Dihaloethanes physisorbed on Si(100), observed by STM for the first time.•Electron-induced reaction gives directed long-range migration of ethylene.•Simulations explain migration dynamics in terms of ‘ballistics’ and ‘bounce’.