Interaction gas-surface

Barker J A and Auerbach D J 1985 Gas-surface interactions and dynamics thermai energy atomic and moiecuiar beam studies Surf. Sci.Rep. 4 1... 

Rettner C T and Ashfoid M N R 1991 Dynamics of Gas-Surface Interactions (London Royai Society of Chemistry)... 

Barker J A and Rettner C T 1992 Accurate potentiai energy surface for Xe/Pt(111) a benchmark gas-surface interaction potentiai J. Chem. Phys. 97 5844... 

Tully J C 1980 Dynamics of gas-surface interactions reactions of atomic oxygen with adsorbed carbon on platinum J. Chem. Phys. 73 6333... 

Polanyi J C and Rieley H 1991 Photochemistry in the adsorbed state Dynamics of Gas-Surface Interactions ed C T Rettner and M N R Ashfold (London Royal Society of Chemistry) p 329... 

Gas-surface interactions and reactions on surfaces play a crucial role in many technologically important areas such as corrosion, adhesion, synthesis of new materials, electrochemistry and heterogeneous catalysis. This chapter aims to describe the interaction of gases with metal surfaces in terms of chemical bonding. Molecular orbital and band structure theory are the basic tools for this. We limit ourselves to metals. 

The alternate approach to developing interaction potentials is to consider the solid surface as a very large molecule. One can then apply theoretical techniques based on gas-phase reaction ideas. The simulation of real systems, however, often requires that both reactive adsorbed atoms as well as a large number of substrate atoms be explicitly treated, and so these techniques rapidly become computationally infeasible. It is apparent that to simulate the general situation, bonding ideas from both regimes should be used. This breakdown does, however, provide a useful format within which to discuss intermediate-range interaction potentials, and so it will be used to illustrate potentials which are in current use in simulations of gas-surface interactions. 

Measurement of heat of adsorption by means of microcalorimetry has been used extensively in heterogeneous catalysis to gain more insight into the strength of gas-surface interactions and the catalytic properties of solid surfaces [61-65]. Microcalorimetry coupled with volumetry is undoubtedly the most reliable method, for two main reasons (i) the expected physical quantities (the heat evolved and the amount of adsorbed substance) are directly measured (ii) no hypotheses on the actual equilibrium of the system are needed. Moreover, besides the provided heat effects, adsorption microcalorimetry can contribute in the study of all phenomena, which can be involved in one catalyzed process (activation/deactivation of the catalyst, coke production, pore blocking, sintering, and adsorption of poisons in the feed gases) [66]. 

The measurement of heats of adsorption by means of microcalorimetry has been used extensively in heterogeneous catalysis in the past few decades to gain more insight into the nature of gas-surface interactions and the catalytic properties of solid surfaces. Specific attention will be focused on group IIIA containing samples in this section. 

Cabrera, N., and Goodman, F. O. (1972). Summation of pairwise potentials in gas-surface interaction calculations. J. Chem. Phys. 56, 4899-4902. 

Early field ion emission studies of gas-surface interactions use field ionization mass spectrometry. Gas molecules are supplied continuously to the tip surface by a polarization force and by the hopping motion of the molecules on the tip surface and along the tip shank. These molecules are subsequently field ionized. The role of the emitter surface in chemical reactions is not transparent and has not been investigated in detail. Only in recent pulsed-laser stimulated field desorption studies with atom-probes are these questions addressed in detail. We now discuss briefly a preliminary study of reaction intermediates in NH3 formation in pulsed-laser stimulated field desorption of co-adsorbed hydrogen and nitrogen,... 

Gas-surface interactions 4.5.3 Some field induced effects... 

Two techniques are principally responsible for the experimental development of dynamics in surface chemistry. These are the application of molecular beams and laser state-to-state techniques to gas-surface interactions. This roughly parallels their application to gas phase chemistry, although there are certainly some different technical requirements. More detailed discussion of some of these experimental techniques are in Refs. [104] and [105]. 

The cleaning of the various catalyst samples has to be scrutinized for each material studied. For iron for example, the major impurity is sulfur, and its removal must be carried out outside the vacuum system in a furnace in a constant hydrogen flow for a long period of time (days). Trace metallic impurities or nonmetallic impurities may be removed either by argon ion bombardment in the vacuum chamber or by chemical treatment using gas-surface interactions of different types. 

Figure 3. Ranges of kinetic energy and equivalent flux density of incident species for various engineering applications for ion-surface and gas-surface interactions. Kinetic energy ranges of particles in which significant interactions occur are also shown. (Reproduced with permission from reference 36. Copyright 1984 American Institute of Physics.)...

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