Reactive and nonreactive scattering of modulated molecular beams from well characterized platinum single crystal surfaces. [Mechanism, rainbow scattering, angular distribution]

Technical Report · Fri Dec 01 04:00:00 EST 1978

DOI:https://doi.org/10.2172/6229231· OSTI ID:6229231

Gale, R J

Reactive and nonreactive gas-surface interactions were studied by modulated molecular beam mass spectrometry on Pt(111) and stepped Pt(111) surfaces under ultra-high vacuum conditions. The angular distribution of helium atoms scattered from the stepped Pt(553) surface was measured as a function of the angle of incidence (polar, theta, and azimuthal, Phi). Rainbow scattering was observed indicating that the ordered array of steps and terraces exhibits a strongly periodic surface potential. In contrast, from the Pt(111) surface, the angular distribution of scattered helium atoms exhibits a sharp peak at the specular angle, characteristic of a smooth and well ordered surface. The interaction of hydrogen with platinum was investigated by studying the H/sub 2/-D/sub 2/ exchange reaction on the Pt(111) and the two stepped surfaces, Pt(553) and Pt(332). The production of HD was monitored. The mechanism of the H/sub 2/-D/sub 2/ exchange reaction was investigated on the Pt(111) and stepped Pt(332) surfaces. The dependence of the apparent reaction probability on surface temperature also indicates that the adsorption of hydrogen is an activated process on the Pt(111) surface, but not on the stepped Pt(332) surface. The energy barrier for hydrogen adsorption on Pt(111) deduced from this type of experiment is approx. 1.5 kcal/mole. On both surfaces, the mechanism of the recombination of adsorbed H and D atoms to form HD consists of a branched process at high crystal temperatures, with one of the branches connected in series with another reaction step at low temperatures. The process that isoperative over the entire temperature range studied, 25 to 800/sup 0/C, has an activation energy and an apparent pre-exponential factor 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.

• Research Organization: California Univ., Berkeley (USA). Lawrence Berkeley Lab.
• DOE Contract Number: W-7405-ENG-48
• OSTI ID: 6229231
• Report Number(s): LBL-7687
• 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
ANGULAR DISTRIBUTION
ATOM COLLISIONS
BEAMS
COLLISIONS
CRYOGENIC FLUIDS
DATA
DATA FORMS
DEUTERIUM
DISTRIBUTION
ELASTIC SCATTERING
ELEMENTS
EXPERIMENTAL DATA
FLUIDS
GASES
HELIUM
HYDROGEN
HYDROGEN ISOTOPES
INFORMATION
ISOLATED VALUES
ISOTOPES
KINETICS
LIGHT NUCLEI
MASS SPECTROSCOPY
METALS
MODULATION
MOLECULAR BEAMS
NONMETALS
NUCLEI
NUMERICAL DATA
ODD-ODD NUCLEI
PLATINUM
PLATINUM METALS
POTENTIAL SCATTERING
POTENTIALS
PROBABILITY
RARE GASES
RECOMBINATION
SCATTERING
SORPTION
SPECTROSCOPY
STABLE ISOTOPES
SURFACE POTENTIAL
SURFACES
TEMPERATURE DEPENDENCE
TRANSITION ELEMENTS
ULTRAHIGH VACUUM
VARIATIONS