NEXAFS Study On The Adsorption And Reaction Of SO₂/Ag(110),Cu(100) And C₂D₂/Si(111)7×7

In recent years, the adsorption and reaction of both sulfur dioxide on transition metals and acetylene on silicon have received much attention because of their importance in surface science researches and applications. The rich characters of surface physics and chemistry have been revealed based on the experimental investigations in the above fields, but the quantitative investigations on theory are seldom. In this thesis, both the multiple scattering cluster (MSC) method and the discrete variational-Xα(DV-Xα) method have been employed to make a theoretical investigation on three adsorption systems of SO2/Ag(110), (SO+2O)/Cu(100) and C2D2/Si(111)7×7. The adsorption structures of above three adsorption systems are determined and the physical cause of their NEXAFS resonances are revealed by our theoretical investigation.Silver is the only metal on whose clean surface no decomposition of SO2 has been observed. The MSC method has been used to perform the theoretical analysis for sulphur K-edge NEXAFS of SO2 adsorbed on Ag(110) at half monolayer. It is shown that SO2 is adsorbed on Ag(110) taking the hollow site with the coordination of sulfur and one oxygen atom bonded, the adsorption height is 1.8±0.1 A, the molecular plane is rotated from the (110) by about 52°and tilted slightly away from the substrate normal. The resonance of no clear polarisation dependence located betweenπ* andσ* is proved to arise from transitions into an antibonding orbital induced by the interaction between SO2 and the substrate.Compared to the gas phase SO2, the O-S intramolecular bond length is elongated by 0.14±0.06A and the OSO bond angle is reduced by 15°±5°after adsorption.The NEXAFS spectra of SO2, on Cu(100) at 280 K have been studied theoretically with MSC method. It has been proved that SO2 is decomposed on Cu(100) at 280 K and form the co-adsorption phase of (SO+2O)/Cu(100). The same adsorption structure as in a SEXAFS study is obtained. Theπ* orbital breaks into two levels which shift towards higher energy due to the interaction between SO and the substrate. The unusual resonance structrures correspond to the Is electrons excited to the twoπ* type orbital. The low unoccupied orbitals of (SO+2O)/Cu(100) are examined by DV-Xαstudy, which demonstrates the molecular orbital properties of the resonances in NEXAFS spectra of the adsorption system and supports the results of MSC calculation.For C2D2/Si(111)7×7 system, its NEXAFS spectra have been analysed by employing MSC method and the electron structures of unoccupied orbitals are studied by DV-Xαmethod. It is deduced that C2D2 is adsorbed on Si(111)7×7 by bonding to the pair of adjacent Si adatom and Si rest atom. The C-D bond is bent and the CCD bond angle is about 1200 after adsorption. The molecule plane is slightly tilt away from the surface normal. Due to the interaction between C2D2 and substrate theπ* orbital parallel to molecule plane moves to higher energy. The adsorption of C2D2 on Si(111)7×7 induce the C-C bond elongated by about 0.3 A and C-D bond increased from 1.05A to 1.25A which makes deuteron atom decomposed easily.