Abstraction of sulfur from Pt(111) surfaces with thermal H atoms toward adsorbed and gaseous H2S

Sulphur layers on Pt(1 1 1) surfaces with coverages of 0.25 and 0.33 were prepared by H2S adsorption at 85 K and subsequent annealing. If,S adsorption on Pt, S/Pt and H/Pt surfaces and S adsorbate layers were characterized by Auger electron and thermal desorption spectroscopies. Admission of thermal H atoms to S covered Pt(I 1 1) at 85 K leads to formation of gaseous (80%) as well as adsorbed H2S (20%). The yield of adsorbed H2S decreases due to its isothermal desorption above 90 K. The interaction of H(g) with S(a) involves three reaction steps: 1. H(g) + S(a) --> SH(a), 2. H (9) + SH(a) --> H2S(g, a), and 3. H(g) + SH(a) --> H,(g) + S(a) with apparent cross-sections sigma = 0.3 Angstrom(2), sigma(2) = 0.6 Angstrom(2) and sigma(3) = 0.03 Angstrom(2). Above 140 K the hydrogenation of SH toward H2S(a,g) is blocked by thermal decomposition of H2S. Impact of D on coadsorbed S, SH, and H'S leads to desorption of H2S. (C) 2002 Elsevier Science B.V. All rights reserved