ADSORPTION OF SO2 ON CU(100) STUDIED BY X-RAY-ABSORPTION FINE-STRUCTURE SPECTROSCOPY AND SCANNING-TUNNELING-MICROSCOPY

The room temperature adsorption of SO2 on Cu(100) was studied using S K-edge X-ray absorption fine structure spectroscopy, Auger electron sp ectroscopy, low energy electron diffraction, X-ray photoelectron spect roscopy, and scanning tunneling microscopy (STM). It is known that the disproportionation reaction 3SO(2)(a)-->S(a)+2SO(3)(a) occurs on the Cu(100) surface. The surface coverages of the reaction product adsorba tes as well as their respective geometric structures are reported. XAF S modeling calculation results indicate that the atomic S adsorbs in t he fourfold hollow site and trigonal pyramidal SO3 adsorbs with the su lfur away from the surface. Thus, the three oxygen atoms are directly bonded to the Cu substrate. STM images show the coexistence of two dif ferent phases of the (2 x 2) and c(4 x 6) domains. The (2 x 2) unit ce ll contains one SO3 species but no S atoms. In contrast, the c(4 x 6) unit cell contains one SO3 and two S atoms. The presence of such domai ns implies a drastic migration of the reaction products on the surface . (C) 1997 Elsevier Science B.V.