Modulated molecular beam study of the mechanism of the H/sub 2/--D/sub 2/ exchange reaction on Pt(111) and Pt(332) crystal surfaces

Journal Article · Thu Mar 15 04:00:00 EST 1979 · J. Chem. Phys.; (United States)

OSTI ID:6269326

Salmerona, M; Gale, R J; Somorjai, G A

The interaction of hydrogen with platinum has been studied by the exchange reaction H/sub 2/+D/sub 2/=2HD on two crystal surfaces, a flat (111) and a stepped (332) (in step notation, (S)-(6(111) x (111))). The adsorption of hydrogen appears to be an activated process on the Pt(111) surface, with a barrier height of approx.0.5--1.5 kcal/mole. On the Pt(332) surface, the adsorption of hydrogen requires no activation energy. The recombination of H and D atoms to form HD follows, on both surfaces, a parallel mechanism with one of the branches operative in the entire temperature range studied, 25--800/sup 0/ C. This branch has an activation energy and pseudo-first-order preexponential of E/sub 1/=13.0 +- 0.4 kcal/mole and A/sub 1/= (8 +- 3) x 10/sup 4/sec/sup -1/ for the Pt(332) surface and E/sub 1/=15.6 +- 0.5 kcal/mole and A/sub 1/= (2.7 +- 1) x 10/sup 5/sec/sup -1/ for the Pt(111) surface. For temperatures above approx.300/sup 0/ C, the second branch is observed, but the values of the preexponential factors and activation energies could not be uniquely determined for either of the two crystals. Below approx.300/sup 0/ C, a third process appears in series with the first branch. The scatter in the data at low temperatures due to the small signal amplitude prevents accurate determination of the rate constants for this reaction step.

• Research Organization: Materials and Molecular Research Division, Lawrence Berkeley Laboratory, and Department of Chemistry, University of California, Berkeley, California 94720
• OSTI ID: 6269326
• Journal Information: J. Chem. Phys.; (United States), Journal Name: J. Chem. Phys.; (United States) Vol. 70:6; ISSN JCPSA
• Country of Publication: United States
• Language: English

Related Subjects

640301* -- Atomic
Molecular & Chemical Physics-- Beams & their Reactions
71 CLASSICAL AND QUANTUM MECHANICS
GENERAL PHYSICS
ADSORPTION
BEAMS
COLLISIONS
CRYOGENIC FLUIDS
CRYSTALS
DATA
DATA FORMS
DEUTERIUM
DISSOCIATION
ELEMENTS
EXPERIMENTAL DATA
FLUIDS
HIGH TEMPERATURE
HYDROGEN
HYDROGEN ISOTOPES
INFORMATION
ISOLATED VALUES
ISOTOPES
KINETICS
LIGHT NUCLEI
MEDIUM TEMPERATURE
METALS
MOLECULAR BEAMS
MOLECULE COLLISIONS
NONMETALS
NUCLEI
NUMERICAL DATA
ODD-ODD NUCLEI
PALLADIUM
PLATINUM
PLATINUM METALS
REACTION KINETICS
SORPTION
STABLE ISOTOPES
SURFACES
TEMPERATURE DEPENDENCE
TRANSITION ELEMENTS