Structure sensitive reaction channels of molecular hydrogen on silicon surfaces

The ability of the Si(001) surface to adsorb H-2 molecules dissociatively i ncreases by orders of magnitude when appropriate surface dangling bonds are terminated by H atoms. Through molecular beam techniques the energy depend ent sticking probability at different absorption sites on H-precovered and stepped surfaces is measured to obtain information about the barriers to ad sorption, which decrease systematically with an increase in coadsorbed H at oms. With the help of density functional calculations for interdimer adsorp tion pathways, this effect is traced back to the electronic Structure of th e different adsorption sites and its interplay with local lattice distortio ns.