Thermal desorption mass spectrometry of oxygen chemisorbed on thermally etched and polycrystalline silver filaments

• Published in: Journal of catalysis Vol. 46; no. 1; pp. 109 - 119
• Main Authors: Ekern, R.J., Czanderna, A.W.
• Format: Journal Article
• Language: English
• Published: Elsevier Inc 1977
• ISSN: 0021-9517; 1090-2694
• DOI: 10.1016/0021-9517(77)90141-5

Thermal desorption spectra for oxygen chemisorbed on thermally etched and polycrystalline silver filaments have been obtained using a modified flash filament technique with mass analysis in an ultrahigh vacuum system. Cleaning and adsorption cycles were carried out at partial pressures <2 × 10 −6 Torr while desorption measurements were obtained in a total pressure environment <5 × 10 −9 Torr. The spectra from the two dissimilar surface structures differ primarily in the number of desorbing phases. For thermally etched silver, a single phase desorbs after exposures to 500–11000 Langmuirs of oxygen at adsorption temperatures of 375–510 °K. The adsorption is activated and the activation energy, E d , for the second order desorption reaction is estimated to be 34 kcal/mole. For polycrystalline silver, two phases desorb after exposures to 500–6000 Langmuirs of oxygen at temperatures of 300–535 °K. The doublet desorption spectra result from a nonactivated adsorbed phase with E d of ca. 27 kcal/mole and an activated adsorbed phase, with E d of ca. 37 kcal/mole. The desorption for both phases from polycrystalline silver is second order in concentration.