Electrons exchange scattering

Scattering and recoiling contribute to our knowledge of surface science tln-ough (i) elemental analysis, (ii) structural analysis and (iii) analysis of electron exchange probabilities. We will consider the merits of each of these tluee areas. 

If the velocity of the incident electron is comparable with those of molecular electrons, the former can be exchanged for one of the latter. Such processes are described by the exchange scattering amplitude, the form of which in the first Born approximation has been found by Oppenheimer.126 In the Born-Oppenheimer approximation the exchange amplitude (4.11) acquires the form... 

However, this difference in factors is quite important since it leads to a different dependence on the energy E of the incident electron, namely, the exchange cross section rapidly decreases with decrease of E ( 1 IE3). Therefore, for fast electrons the exchange scattering can be disregarded. 

The scheme shows that not only the end products, but also the initial molecules could be polarized. Besides, one of the ion radicals formed may exchange electrons with the neutral starting molecule. These phenomena and others, which can be attributed to electron exchange, lead to a loss of memory in nuclear spin states. In addition, the initial polarization may be scattered as a result of a chain ion radical process. This is illustrated in the following scheme (Chanon Tobe 1982) ... 

P. Krylstedt, N. Elander, E. Brandas, A Complex Dilated Study of Shape Resonances and Negative Ions in Electron-Atom Scattering, within an Asymptotic Complete Form of Continuum Exchange, J. Phys. B At. Mol. Opt. Phys. 22 (1989) 1623. 

X-ray and neutron diffraction and scattering techniques. The equilibrium between Fe + aq and FeOH + aq and the kinetics and mechanisms of their reactions with ligands, including environmentally relevant humic and fulvic acids (see Section 4.11) and pharmacologically relevant desferrioxamine, have been reviewed, as have complex formation reactions of [Fe (/u-OH)2Fe ] + (Ref 300) and of Fe +aq, for example, with NO, and electron exchange between Fe +aq and Fe +aq/FeOH + aq. ... 

The use of polarised beams in collision studies has enabled experimentalists to perform very detailed tests of theoretical models, particularly with regard to the role of electron exchange and the spin—orbit interaction in spin-dependent scattering. We will now briefly discuss the role of these interactions before using the general density matrix method to describe the more general case where more than one mechanism may contribute to the spin-dependent effects. 

The role of exchange scattering can be observed most clearly when polarised electrons are scattered from a target of polarised light atoms. If one observes a spin-flip process like... 

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