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 spectroscopy, low energy electron diffraction, X-ray photoelectron spectroscopy, 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 adsorbates as well as their respective geometric structures are reported. XAFS modeling calculation results indicate that the atomic S adsorbs in the fourfold hollow site and trigonal pyramidal SO3 adsorbs with the sulfur away from the surface. Thus, the three oxygen atoms are directly bonded to the Cu substrate. STM images show the coexistence of two different phases of the (2 x 2) and c(4 x 6) domains. The (2 x 2) unit cell 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 domains implies a drastic migration of the reaction products on the surface. (C) 1997 Elsevier Science B.V.