Role of interdimer interactions in NH3 dissociation on Si(100)-(2 x 1)

The dissociation of NH3 on Si(100)-(2 x 1) is investigated by a combination of infrared absorption spectroscopy and density functional cluster calcula tions, revealing that this reaction is governed by a complex set of interdi mer interactions involving both bare and adsorbate-covered Si dimers. We pr opose that such adsorbate-induced changes in the electronic structure of ne ighboring dimers may have general implications for controlling the two-dime nsional ordering of reactions on the dimerized Si(100) surface.