The University of Southampton
University of Southampton Institutional Repository

The role of steps in the dynamics of hydrogen dissociation on Pt(533)

Gee, A. T., Hayden, B. E., Mormiche, C. and Nunney, T. S. (2000) The role of steps in the dynamics of hydrogen dissociation on Pt(533) The Journal of Chemical Physics, 112, (17), pp. 7660-7668. (doi:10.1063/1.481360).

Record type: Article


The dissociative adsorption of H-2 and D-2 on Pt(533) (Pt{4(111)x(100)}) has been investigated using temperature programmed desorption and supersonic molecular beams. Associative desorption of D-2 from (100) step sites is observed at lowest exposures in TPD (assigned beta(3)) at 375 K. Saturation of this peak at Theta(H)=0.14 corresponds to the filling of half of the available four-fold sites at the (100) step edge. At higher coverages, additional desorption takes place from the (111) terraces in a broad peak below 300 K similar to that observed (assigned beta(1) and beta(2)) for the Pt(111) surface. The incident kinetic energy (E-i), surface temperature (T-s), coverage (Theta(D)), and incident angle (Phi) dependence of the dissociative sticking probability (S) was also measured. The initial dissociative sticking probability (S-0) first decreases with increasing kinetic energy over the range 0 < E-i(meV)< 150 (low energy component), and subsequently increases (high energy component). Comparison with D-2 dissociation on Pt(111), where (S-0) increases linearly with E-i, leads to the conclusion that it is the step sites that are responsible for the low energy component to dissociation on Pt(533). The high energy component is a result of a direct dissociation channel on (111) terraces of the Pt(533) surface. The probability of dissociation through the direct channel on the (111) terraces is found to be independent of T-s. The probability of dissociation through the low energy component associated with the (100) steps, over most of the range of E-i where it contributes, is also shown to be independent of T-s. Only at the very lowest value (6.6 meV) of E-i investigated does S-0 exhibit a (negative) temperature dependence. A (0.8-Theta(D))(2) dependence (where 0.8 is the measured saturation coverage) of S with Theta(D) is observed at E-i=180 meV where the direct channel dominates. However, the dependence of S on Theta(D) exhibits characteristics similar to those expected for precursor mediated dissociation at E-i=16 meV and E-i=6.6 meV where the low energy channel dominates. The angular dependence S-0(Phi) scattering in a plane perpendicular to the step direction is asymmetric about the Pt(533) surface normal at both E-i=6.6 meV and E-i=180 meV. At 180 meV S-0(Phi) can be understood by considering direct dissociation at the (111) terrace and (100) step plane. At 6.6 meV, S-0 tends to scale with total energy. The observed characteristics of the low energy channel is discussed in the light of models [specifically the role steps and defects, precursors (accommodated and dynamical), and steering] suggested to account for the low energy component for H-2/D-2 dissociation and exchange on metal surfaces presenting low activation barriers. At lowest energies (E-i=6.6 meV) dissociation through a conventional accommodated precursor takes place. In addition, more significant proportion of sticking in the range 0 < E-i(meV)< 150 takes place through an indirect channel involving an unaccommodated precursor dissociating at step sites, and is unlikely to be accounted for through a steering mechanism.

Full text not available from this repository.

More information

Published date: 1 May 2000
Keywords: platinum crystal-surfaces, molecular-beam, metal-surfaces, sticking probability, adsorption-kinetics, exchange-reaction, pt(111) surface, reactant angle, h-2, mechanism


Local EPrints ID: 18921
ISSN: 0021-9606
PURE UUID: f3f99c29-0bab-4955-a649-0add60bb55e5

Catalogue record

Date deposited: 21 Dec 2005
Last modified: 17 Jul 2017 16:34

Export record



Author: A. T. Gee
Author: B. E. Hayden
Author: C. Mormiche
Author: T. S. Nunney

University divisions

Download statistics

Downloads from ePrints over the past year. Other digital versions may also be available to download e.g. from the publisher's website.

View more statistics

Atom RSS 1.0 RSS 2.0

Contact ePrints Soton:

ePrints Soton supports OAI 2.0 with a base URL of

This repository has been built using EPrints software, developed at the University of Southampton, but available to everyone to use.

We use cookies to ensure that we give you the best experience on our website. If you continue without changing your settings, we will assume that you are happy to receive cookies on the University of Southampton website.