Abstraction of sulfur from Pt(1 1 1) 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. H2S 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(1 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(g)+SH(a)→H2S(g,a), and 3. H(g)+SH(a)→H2(g)+S(a) with apparent cross-sections σ1=0.3 Å2, σ2=0.6 Å2 and σ3=0.03 Å2. 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 H2S leads to desorption of H2S.