Modulated molecular beam scattering of CO and NO from Pt(111) and the stepped Pt(557) crystal surfaces
The modulated molecular beam scattering of CO and NO from Pt(111) and Pt(557) have been studied in the temperature range of 350-1100 K. For CO scattered from Pt(111), an adsorption-desorption model with constant sticking coefficient fits the data well above 500°K, The best rate parameters are: {nu}=2.9x10{sup 13}, E=29.9 kcal/mole, and S=0.74. For CO scattered from Pt(557) the same model fits the data well above 550°K and the best rate parameters are {nu}=7.9x10{sup 13}, E=33.6 kcal/mole, and S=0.74. The higher activation energy for desorption from the stepped Pt(557), as compared to the flat Pt(111), suggests that while the incident molecules can be adsorbed at the step as well as at the terrace, their desorption energy is influenced by the presence of steps. An adsorption-desorption model with coverage-dependent sticking coefficient fits the data obtained at all temperatures well for both surfaces without change of the kinetic parameters. For NO scattered from Pt(111), the adsorption-desorption model with constant sticking coefficient fits the data well above 525°K using the rate parameters of {nu}=6.2x10{sup 13}, E=28.6 kcal/mole, and S=0.65. For NO scattered from Pt(557), the same model fits the data well above 525°K with {nu}=1.2x10{sup 14}, E=32.3 kcal/mole, and S=0.71. The higher activation energy suggests again that NO desorption is influenced by the presence of steps. Below 525°K, the NO scattering results are quite different from those of CO and can not be simulated with the simple models that were tried. The data can be used, however, to rule out several models of surface interactions. NO does not dissociate detectably between 400 K ~1200 K under our experimental conditions. The sticking coefficient decreases with increasing coverage.
- Research Organization:
- Ernest Orlando Lawrence Berkeley National Laboratory, Berkeley, CA (US). Materials Sciences Division
- Sponsoring Organization:
- USDOE
- DOE Contract Number:
- AC02-05CH11231
- OSTI ID:
- 1108709
- Report Number(s):
- LBL-11787
- Journal Information:
- Surface Science, Journal Name: Surface Science Journal Issue: 2-3 Vol. 107; ISSN 0039-6028
- Country of Publication:
- United States
- Language:
- English
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