PHOTOCHEMISTRY OF SO2 ON AG(111)

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 (DELTA-PHI). 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) x 10(-20) cm2 at (313 +/- 10) nm. The wavlength 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.