Adsorption dynamics of water on Pt{110} - (1×2)

Fathima R. Laffir, Vittorio Fiorin, David A. King

Research output: Contribution to journalArticlepeer-review

Abstract

The dynamics of H2 O adsorption on Pt {110} - (1×2) is studied using supersonic molecular beam and temperature programed desorption techniques. The sticking probabilities are measured using the King and Wells method at a surface temperature of 165 K. The absolute initial sticking probability s0 of H2 O is 0.54±0.03 for an incident kinetic energy of 27 kJmol. However, an unusual molecular beam flux dependence on s0 is also found. At low water coverage (θ<1), the sticking probability is independent of coverage due either to diffusion in an extrinsic precursor state formed above bilayer islands or to incorporation into the islands. We define θ=1 as the water coverage when the dissociative sticking probability of D2 on a surface predosed with water has dropped to zero. The slow falling H2 O sticking probability at θ > 1 results from compression of the bilayer and the formation of multilayers. Temperature programed desorption of water shows fractional order kinetics consistent with hydrogen-bonded islands on the surface. A remarkable dependence of the initial sticking probability on the translational (1-27 kJmol) and internal energies of water is observed: s0 is found to be essentially a step function of translational energy, increasing fivefold at a threshold energy of 5 kJmol. The threshold migrates to higher energies with increasing nozzle temperature (300-700 K). We conclude that both rotational state and rotational alignment of the water molecules in the seeded supersonic expansion are implicated in dictating the adsorption process.

Original languageEnglish
Article number114717
JournalJournal of Chemical Physics
Volume128
Issue number11
DOIs
Publication statusPublished - 2008
Externally publishedYes

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