SO2 ADSORPTION ON PT(111) - HREELS, XPS AND UPS STUDY

The chemistry of SO2 on Pt(111) has been studied by X-ray photoelectro n spectroscopy (XPS), ultraviolet photoelectron spectroscopy (UPS), te mperature programmed desorption (TPD) and high resolution electron ene rgy loss spectroscopy (HREELS). At 100 K, SO2 adsorbs molecularly thro ugh the S and one O atom. Photoemission results indicate that signific ant charge transfer occurs between the Pt d-band and the lowest unoccu pied molecular orbital of SO2. Molecular orbital analysis reveals that atop and two-fold sites are energetically feasible for SO2 adsorption , but two-fold sites are more favorable. Upon heating to 300 K, SO2 mo lecules undergo desorption and dissociation. The latter leads to adsor bed S, SO and SO4. An SO2 lattice vibration mode was observed by HREEL S when an SO2 multilayer was dosed at 100 K; and it was enhanced when SO2 was dosed at 110 K. There is a resonance in this feature as the in cident electron energy is varied, which implies that a nondipolar scat tering process contributes. Multilayer SO2, formed upon adsorption at 100 K, is metastable.