Monte Carlo calculation of thermal desorption spectra: Application to CO/Ru(001)

A kinetic lattice gas model is used to study the equilibrium properties and the desorption kinetics of CO on Ru(0001). The authors compute all relevant on-site binding and interaction energies of CO molecules within density functional theory and import them in two different models. The first model allows the CO molecules to adsorb upright on top and hollow sites. The authors calculate the phase diagram, coverage isobars, and temperature programed desorption spectra. Up to a coverage of 1/3 ML, very good agreement is obtained between theory and experiment when considering top sites only. For coverages beyond 1/3 ML, hollow sites are included and disagreement between theory and experiment occurs. The second model allows adsorption on top sites only but allows them to tilt and shift from their upright positions. The authors show that this model resolves many of the deficiencies of their first one. Furthermore, the authors demonstrate that this model is more consistent with experiment since it is the only model that is able to explain the results from IR-spectroscopy experiments.

“…This would give a phase diagram similar to that given in Fig. 1 but with a tricritical point that one can estimate [32] to be 75 K instead of ∼ 120 K as shown in Fig. 1.…”

Section: Modeling With On-top Sites At Low Coveragementioning

confidence: 75%

Section: Modeling With On-top Sites At Low Coveragementioning

confidence: 99%

Section: Modeling With On-top Sites At Low Coveragementioning

confidence: 99%

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Phase diagram and adsorption-desorption kinetics of CO on Ru(0001) from first principles

McEwen

Eichler

2007

“…The hard hexagon model is of interest for two reasons. Firstly, it appears to explain some experimental results in surface science and electrochemistry [15][16][17][18][19][20] . Secondly, as a model system with a phase transition and an analytical solution, it can be used to verify methodologies independently of any experimental or theoretical approximations.…”

Section: Introductionmentioning

confidence: 98%

The role of available sites in the activity of lattice gases with geometric constraints

Strobl

Harrington

2013

The activity in lattice-gas systems with geometric constraints is shown to be the ratio of the number of particles to the number of available sites. The key role of sites available for occupation is emphasized. Available sites may be different for different species and are not necessarily just unoccupied sites. Location-specific or non-local constraints are allowed. An analytical expression for the number of available sites is given for the hard-hexagon model. The utility of an expression for available sites is illustrated for the non-trivial case of a mixed Langmuir/hard-hexagon adsorption system, where the influence of the Langmuir adsorbates on the hard-hexagon phase transition is investigated. The dependence on available sites indicates how to extend these results to the kinetic regime and simulations of kinetic voltammograms for the hard-hexagon model are given as an example.

“…This expression, still in use, 19 obviously diverges as →1, yet it has been frequently claimed that this explosion of k des is physically correct in approximately accounting for adsorbate interactions at high coverages 16 or for ''the excluded volume effect, i.e., that no more than one particle can occupy a single lattice gas site.'' 17 These conclusions have previously been questioned in the literature.…”

Section: ͑12͒mentioning

confidence: 99%

The application of transition state theory to gas–surface reactions in Langmuir systems

Pitt

Gilbert

Ryan

1995

Quantum state-resolved gas/surface reaction dynamics probed by reflection absorption infrared spectroscopy Rev. Sci. Instrum. 84, 053902 (2013) Transition state theory ͑TST͒ has long been applied to gas-surface reactions for the purpose of characterizing and predicting desorption rate coefficients, but current perceptions of its use exclude TST from meaningful description of the sticking coefficient for partially covered surfaces. This paper re-examines the application of TST to partially covered surfaces, and in particular to Langmuir systems with barrierless adsorption. An analogy is drawn in the present work between barrierless adsorption processes and gas-phase radical-radical recombination reactions that reveals a simple method by which TST can describe kinetics in Langmuir systems. Construction of a model ''hard-wall'' Hamiltonian that reflects the exclusion of adsorbates from occupied sites enables the kinetics in Langmuir systems to be described by constructing a transition state surface that does not permit adsorption at occupied sites. This method gives analytic expressions for the TST sticking coefficient ͑and desorption rate coefficient͒ in two important limiting cases for the gas-surface dynamics, and resolves previous difficulties in the TST description of Langmuir systems.