We present a detailed analysis of a fully ab initio molecular-dynamics simulation of the surface reaction for ${\mathrm{Cl}}_2$ molecules incident on Si(111)-2×1 at an energy of 1 eV. We find that ${\mathrm{Cl}}_2$ adsorption on Si(111)-2×1 is dissociative with short-lived molecular precursor states involved in certain dissociation geometries. Dissociation is accompanied by an enormous surface response causing large, localized rehybridization effects in the π-bonded chains and excitation of vibrational modes in the substrate. Analysis of the charge density in the bond within the molecule during the breakup shows that the dissociation is chemically driven and proceeds by transferring charge to a more antibonding molecular orbital.

• Received 16 August 1993

DOI:https://doi.org/10.1103/PhysRevB.49.8076