Multiple electron scattering

This result is in general agreement with an extensive analysis of the electron scattering of multiple rotor molecules by J. Karle206, who studied the effect on the intensity and the RD-curve in cases with low barrier and geared motion. 

Smith IM, Thompson DG, Blum K (1998) Chiral effects in electron scattering by molecules using a continuum multiple scattering method. J Phys B 31 4029... 

In any of the steps 1, 3 and 4, multiple scattering of electrons can play an important role in the techniques of interest here. On the one hand, multiple scattering provides a greater sensitivity to various aspects of structure on the other hand, it complicates the theoretical treatment, i.e. it complicates the extraction of the structural information. For the following discussion it will be useful to first describe in more detail a couple of important features of electron scattering by individual atoms in a surface. 

We have just described electron scattering by a single atom. The main feature to remember is the pronounced forward scattering within a more or less narrow forward cone, which occurs especially at the higher energies. The implications for multiple scattering are as follows. 

There are situations in which crystallites are readily visible, especially on supports which do not offer excessive electron scatter. In these cases, metal content can be quantitatively determined for areas which have highly dispersed metal and agglomerated metal. This information in conjunction with the crystallite size distribution provides the microscopist with the information required to make an estimate of metal dispersion (13). These estimates are valuable especially in situations where conventional gas adsorption measurements cannot be made on the metal, i.e., when the crystallites are contaminated, have multiple oxidation states, or are poisoned. 

Statistical theory of electron densities - multiple-scattering perturbation theory. Proc. Roy. Soc. London A 435, 245-255 (1991). 

---