The adsorption and surface reactions of ICN on the Si(100)-(2 x 1) surface are studied using ab initio quantum calculations on model dimer clusters. ICN can physisorb via a dative bond through the N atom. This species can further react to form either a dissociated state through I-CN bond cleavage or a stable side-on intermediate by reacting across the dimer bond. There are two important differences between the ICN adsorption process and that of HCN. Unlike HNC, the INC dative bonded structure is not stable. Next, there is no transition state between the side-on adsorbed ICN and INC species. (C) 2003 Elsevier Science B.V. All rights reserved.