Laser-induced thermal desorption studies of simple adsorbates on single crystal metal and oxide surfaces

Miscellaneous · Wed Jan 01 00:00:00 EST 1992

OSTI ID:7274915

Meixner, D L

The surface diffusion of xenon on Pt(III) was studied at temperatures between 45 K and 85 K. The kinetic parameters for surface diffusion at commensurate monolayer coverage [Theta] = [Theta][sub S], were E[sub dif] = 1.3 [+-] 0.1 kcal/mole and D[sub 0] = 1.1 x 10[sup [minus]4[+-]0.2] cm[sup 2]/sec. The magnitude of E[sub dif] at [Theta] = [Theta][sub S] represented the combined effect of the intrinsic corrugation of the absorbate-surface potential and attractive interactions between the adsorbed xenon atoms. The surface diffusion coefficient of xenon on Pt(111) decreased with increasing surface coverage. A likely explanation for the coverage dependence of the surface diffusion coefficient for xenon on Pt(111) was a multiple site diffusion mechanism, possibly from the edges of two-dimensional condensed phase xenon islands. The surface diffusion coefficient of krypton on Pt(111) at 45 k decreased similarly to the results for xenon on P(111). The surface diffusion coefficient of methane on Pt(111) at 45 K was independent of surface coverage at D = 1 x 10[sup [minus]6] cm[sup 2]/sec. LITD techniques were used to investigate kinetic processes on a single crystal oxide surface. The desorption of CO[sub 2] from MgO(100) was found to display coverage-dependent first order kinetics, with an activation energy for desorption that decreased with increasing CO[sub 2] coverage. The low coverage sticking coefficient for CO[sub 2] on MgO(100) was found to decrease with increasing temperature between 100 K and 125 K, consistent with a precursor-mediated adsorption model. Desorption kinetic experiments for HCOOH, MeCOOH, CF[sub 3]COOH, and MeOH on MgO(100) yielded similar results for all four adsorbates studied, suggesting that the Lewis base character generally assigned to polycrystalline magnesium oxide samples was reduced for the flat MgO(100) surface. Surface diffusion coefficients for species studied on MgO(100) were below the detection limits of the LITD experiment.

• Research Organization: Stanford Univ., CA (United States)
• OSTI ID: 7274915
• Resource Relation: Other Information: Thesis (Ph.D.)
• Country of Publication: United States
• Language: English

Related Subjects

37 INORGANIC
ORGANIC
PHYSICAL AND ANALYTICAL CHEMISTRY
36 MATERIALS SCIENCE
CARBON DIOXIDE
DESORPTION
KRYPTON
DIFFUSION
MAGNESIUM OXIDES
SURFACE PROPERTIES
METHANE
PLATINUM
XENON
ACETIC ACID
FORMIC ACID
METHANOL
THERMODYNAMIC PROPERTIES
ALCOHOLS
ALKALINE EARTH METAL COMPOUNDS
ALKANES
CARBON COMPOUNDS
CARBON OXIDES
CARBOXYLIC ACIDS
CHALCOGENIDES
ELEMENTS
FLUIDS
GASES
HYDROCARBONS
HYDROXY COMPOUNDS
MAGNESIUM COMPOUNDS
METALS
MONOCARBOXYLIC ACIDS
NONMETALS
ORGANIC ACIDS
ORGANIC COMPOUNDS
OXIDES
OXYGEN COMPOUNDS
PHYSICAL PROPERTIES
PLATINUM METALS
RARE GASES
SORPTION
TRANSITION ELEMENTS
400201* - Chemical & Physicochemical Properties
360104 - Metals & Alloys- Physical Properties
360204 - Ceramics
Cermets
& Refractories- Physical Properties