Using a first-principles density functional approach, we investigate the chemisorption mechanism for the interaction of spherosiloxane (H8Si8O12) clusters on Si(100). Our transition state studies reveal that the chemisorption pathway with the lowest activation barrier corresponds to attachment via Si-O bond cleavage across a surface dimer. Using the relaxed surface structure from this "cracked cluster" model, we calculate Si 2p core-level shifts, including core-hole relaxation effects, and show that the calculated values are in excellent agreement with the positions and intensities of all the experimentally observed core-level shifts. (C) 2000 American Institute of Physics. [S0003-6951(00)00526-X].