Adsorption of thermal D atoms on Sn/Pt(111) surface alloys

The adsorption of D atoms on Pt(111) and two, well-defined Pt-Sn surface alloys - the p(2 × 2) Sn/Pt(111) with Θ_Sn=0.25 ML and (√3 × √3)R30° Sn/Pt(111) with Θ_Sn=0.33 ML - has been investigated by using TPD in order to probe the influence of alloyed Sn on Pt-D interactions. Because these alloys do not dissociatively chemisorb room-temperature, ground-state D₂ under UHV conditions, adsorption of thermal D atoms on the alloys was achieved by using a resistively heated Pt tube source operated at 1300 K. Alloying with Sn decreases the saturation coverage of D adatoms from 0.95 ML on the Pt(111) surface to 0.68 and 0.51 ML on the two alloys, respectively, with increasing Sn concentration. The D atom initial sticking coefficient also decreases from 1 to 0.33 to 0.18 in the same series with increasing Sn concentration in these two Pt-Sn surface alloys. Alloying Sn into the Pt(111) surface initially has no effect on the Pt-D bond dissociation energy, D(Pt-D), with D(Pt-D)=252 kJ mol^-1 on both Pt(111) and the (2 × 2) alloy, but increasing the surface Sn concentration to 0.33 ML and removing the pure-Pt threefold sites in forming the (√3 × √3)R30° alloy causes a 10% decrease in the Pt-D bond energy to 232 kJ mol^-1.