Molecular beams scattering

The nature of reaction products and also the orientation of adsorbed species can be studied by atomic beam methods such as electron-stimulated desorption (ESD) [49,30], photon-stimulated desoiption (PDS) [51], and ESD ion angular distribution ESDIAD [51-54]. (Note Fig. VIII-13). There are molecular beam scattering experiments such... 

This section discusses how spectroscopy, molecular beam scattering, pressure virial coeflScients, measurements on transport phenomena and even condensed phase data can help detemiine a potential energy surface. 

Lykke K R and Kay B D 1990 State-to-state inelastic and reactive molecular beam scattering from surfaces Laser Photoionization and Desorption Surface Analysis Techniquesvo 1208, ed N S Nogar (Bellingham, WA SPIE) p 1218... 

Fluendy MAD and Lawley K P 1973 Applications of Molecular Beam Scattering (London Chapman and Hall)... 

Engel T and Rieder K H 1982 Structural studies of surfaces with atomic and molecular beam diffraction Structural Studies of Surfaces With Atomic and Molecular Beam Scattering (Springer Tracts in Modern Physics vol 91) (Berlin Springer) pp 55-180... 

Figure B2.3.1. Schematic diagram of an idealized molecular beam scattering experiment.

A molecular beam scattering experiment usually involves the detection of low signal levels. Thus, one of the most important considerations is whether a sufficient flux of product molecules can be generated to allow a precise measurement of the angular and velocity distributions. The rate of fonnation of product molecules, dAVdt, can be expressed as... 

Siska P E 1973 Iterative unfolding of intensity data, with application to molecular beam scattering J. Chem. Rhys. 59 6052-60... 

It is difficult to observe tliese surface processes directly in CVD and MOCVD apparatus because tliey operate at pressures incompatible witli most teclmiques for surface analysis. Consequently, most fundamental studies have selected one or more of tliese steps for examination by molecular beam scattering, or in simplified model reactors from which samples can be transferred into UHV surface spectrometers witliout air exposure. Reference [4] describes many such studies. Additional tliemes and examples, illustrating botli progress achieved and remaining questions, are presented in section C2.18.4. 

Fig. 5. Rotational temperatures ofNO desorbing from Pt(l 11). The data are representative of data published for (x) neat thermal desorption , ( +) thermal desorption in the presence of coadsorbed C0 ° (solid squares) and (solid triangles) trapping/desorption in molecular beam scattering, (open triangle) reaction limited desorption from NO-NHj complexes, (open circle) and (open square) NHj oxidation reactions. The solid line is for full accommodation. The dashed curve represents results for translational energy measurements in direct inelastic scattering ...

The detailed microscopic description of a chemical reaction in terms of the motion of the individual atoms taking part in the event is known as the reaction dynamics. The study of reaction dynamics at surfaces is progressing rapidly these years, to a large extent because more and more results from detailed molecular beam scattering experiments are becoming available. 

Gold s method has been used by a number of workers, including Siska (1973), who applied it to molecular-beam scattering data, MacNeil and Dixon (1977), who applied it to photoelectron spectra, and Jones et al. (1967), who restored infrared spectra of condensed-phase samples. The author is unaware of any experimental results with this method, however, that illustrate the full potential achievable by constrained methods to be described later in this chapter. In the work of Jones et al., the resulting resolution is probably limited by the inherent breadth of spectral lines observed with condensed-phase samples. 

Local Potential Applied to Instability Problems (Ball Himmelblau) Local Potential Methods in the Study of Kinetic Equations (Nicolis) Low-energy Molecular Beam Scattering, Use of, in Determination of Molecular Forces (Bernstein Muckerman). 

The theory of molecular scattering has now been developed to the point that scattering calculations can be made with an accuracy sufficient for comparison with current experiments. Thus any discrepancy between theory and experiment should be traced to an inadequate knowledge of the interaction potentials, or to experimental errors, rather than to approximations in the collision dynamics. This tighter coupling of theory and experiment should permit a much more fruitful utilization of the results of molecular beam scattering. 

This work was supported in part by the National Science Foundation. It is based on a paper delivered at the General Discussion on Molecular Beam Scattering, 16th - 18th of April, 1973, with some additional comments and more recent references. 

The reactions to which most attention will be directed in this chapter are simple two, three or four atom systems. Thus they are in or on the border of the domain to which scattering theory has been applied and in which direct kinematic experiments (molecular beam scattering) have been undertaken. We do not propose to review the developments in either of these fields in any detail that has been done by others2,6. Instead, a description will be given of some of the theoretical models that have been applied to exothermic reactions that produce excited products. 

Potential energy surfaces can be built starting from experimental data (e.g., bond strengths, geometries, infrared and fluoresence spectra, molecular beam scattering cross sections, viscosity, diffusion coefficients, line broadening... 

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