A COMPARATIVE KINETIC-STUDY OF XENON ADSORPTION ON A FLAT PT(111) AND STEPPED PT(557) AND PT(112) SURFACES

The adsorption and desorption kinetics for Xe on three Pt single crystalline surfaces have been measured using threshold temperature programmed desorption measurements. It has been found that the first-order desorption kinetic parameters at zero coverage for Xe on Pt(111) (Ed0 = 5.73 ± 0.50 kcal/mol; vd0 = 10 12.5±0.9 s-1) are in excellent agreement with measurements made by a modulated molecular beam method [Ed 0 = 5.65 ± 0.35 kcal/mol; vd0 = 10 12.1 s-1]. The presence of step defect sites of varying density on Pt(557) (1/6 defects) and on Pt(112) (1/3 defects) is shown to have a marked influence on Xe desorption kinetics, producing larger values of E d0 ≅ 8.5-8.7 kcal/mol and larger values of v d0 ≅ 1014 s-1 compared to Pt(111). In addition, for Pt(111), slight attractive Xe-Xe interactions are observed, whereas for Xe adsorption on step sites, repulsive Xe-Xe interactions are observed as the steps fill. Xe adsorption kinetics on Pt(111) at 87 K are consistent with an island growth mechanism. In contrast, on Pt(557) and Pt(112), the adsorption process does not seem to produce island growth on the terraces. These results, taken together, show that using Xe, defect sites on metals may be probed effectively with adsorption and desorption kinetic methods. © 1990 American Institute of Physics.