A MOLECULAR-BEAM STUDY OF AMMONIA ADSORPTION ON PT(100)

Ammonia adsorption has been investigated on the hex-R and (1 x 1) face s of the Pt{100} crystal. It is found that adsorption on the hex-R sur face does not lift the surface reconstruction at 150 K, and that no di ssociation of NH3 occurs. In contrast, the (1 x 1) surface exhibits an ability to dissociate NH3. The initial sticking probability is report ed as a function of incident energy and surface temperature, and the r esults indicate that adsorption is direct and non-activated on the cle an hex-R and (1 x 1) surfaces. Sticking probability versus NH3 coverag e measurements reveal that at finite coverages, on both surfaces, ther e is an additional adsorption pathway involving an extrinsic precursor .