Surface chemistry in three dimensions: CO dissociation between two surfaces

Based on self-consistent density functional calculations it is shown that a new dissociation process for CO adsorbed on a Ru(0001) surface is made possible when the distance to a second Ru(0001) surface placed just above it is below some critical value. This `3Dʹ process is more facile than the usual single surface (`2Dʹ) process because indirect adsorbate–adsorbate interactions in the transition state are absent in the `3Dʹ case. The prospects for STM-induced single molecule chemistry and for `3Dʹ catalysts are discussed.