Photochemistry of SO2 on Ag(111)

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Abstract
The thermal and photon‐induced chemistry of SO2 on Ag(111) has been studied using temperature programmed desorption (TPD), Auger electron spectroscopy (AES), and work function change (ΔΦ). SO2 adsorbs reversibly on Ag(111) and desorbs in peaks at 180 and 130 K for monolayer and multilayer, respectively. The work function increases to 0.33 eV upon saturation of the chemisorbed monolayer (ML), but drops to 0.20 eV for a physisorbed multilayer. UV photons (250–542 nm) induce desorption, but not decomposition, of chemisorbed SO2. The photodesorption rate is first order in the photon flux, increases linearly with coverage up to 1 ML, but decreases sharply at higher coverages. For coverages up to 1 ML, the photodesorption cross section is (2.8±0.2)×10−20 cm2 at (313±10) nm. The wavelength dependence is consistent with substrate, including bulk plasmon, excitation. Photodesorption mechanisms involving hot electron and hole attachment processes, only in the first monolayer, are discussed.