Fang Cheng1, Wei Ji2, Lydie Leung1, Zhanyu Ning1, John C. Polanyi1* and Chenguang Wang1,2
1Lash Miller Chemical Laboratories, Department of Chemistry and Institute of Optical Sciences, University of Toronto, 80 St. George Street, Toronto, Ontario, M5S 3H6, Canada.
2Department of Physics and Beijing Key Laboratory of Optoelectronic Functional Materials & Micro-nano Devices, Renmin University of China, Beijing 100872, China.
DOI:10.1021/nn503721h Publication Date:
Interest attaches to the effect of adsorbate alignment in surface reaction. Here we show its significance for electron-induced reaction occurring along preferred axes of the asymmetric surface Cu(110), characterized by directional copper rows. By Scanning Tunneling Microscopy (STM) we found that the heterocyclic aromatic reagent, physisorbed meta-iodopyridine, lay with its carbon-iodine either along the rows of Cu(110), (‘A’), or perpendicular, (‘P’). Electron-induced dissociative attachment with the C-I bond initially along ‘A’ gave a chemisorbed I-atom and chemisorbed vertical pyridyl, singly surfacebound, whereas that with C-I along ‘P’ gave a chemisorbed I-atom and a horizontal pyridyl, doubly-bound. An impulsive two-state model, involving a short-lived anti-bonding state of C-I, accounted for the different product surface-binding in terms of closer Cu. Cu atomic spacing along ‘A’ accommodating only one binding site of the pyridyl ring recoiling from I, and wider spacing along ‘P’ accommodating simultaneously both binding sites, NCu and C-Cu, in the meta- position on the recoiling pyridyl ring. STM studies combined with dynamical modeling can be seen to be opening the way to improved understanding of the role of surface alignment in determining reactive outcomes in induced reaction at asymmetric crystalline surfaces.