Theoretical studies of near-edge X-ray absorption fine structure for SO<SUB>2</SUB>/Ag(110)

The theoretical analysis for sulfur K-edge near-edge X-ray adsorption fine structure of SO₂ adsorbed on Ag(110) at half monolayer has been performed by using the multiple-scattering cluster method. The resonance located between π* and σ* is proved to arise from transitions into an antibonding orbital induced by the interaction between SO₂ and the substrate and its unclear polarisation dependence is found to be caused by the slight tilt of SO₂ molecular plane away from the surface normal. Compared to gas phase SO₂, the O–S intramolecular bond length is elongated by 0.17±0.03 Åand the OSO bond angle is reduced by 15°±5° after adsorption. It is concluded that SO₂ is adsorbed on Ag(110) with the S atom sitting in a hollow site and the two O atoms being in asymmetric geometry, that the adsorption height is 1.8±0.1 Åand that the molecular plane rotates about 52° from the [001] azimuth and tilts slightly away from the surface normal.