Electronic structure neutron scattering

Numerous studies have attempted to solve the low temperature structure by various techniques X-ray and electron diffraction neutron scattering These results may be summarized briefly as follows. 

Analytical Techniques. Analytical techniques to determine the structure of carbon fibers include wide-angle and small-angle x-ray diffraction, electron diffraction, neutron scattering, Raman spectroscopy, electron microscopy, and optical microscopy. Detailed reviews of these techniques are found in the literature. ... 

Hall, L. H. (ed.), Structure of Crystalline Polymers , Elsevier, New York, 1984. The book emphasizes the experimental techniques used to study polymer structure, including use of the digital computer, wide angle X-ray diffraction electron microscopy, neutron scattering and X-ray scattering. 

The zero order term, is obtainable from x-ray, electron, or neutron scattering via Fourier transformation. This is true, however, only if no orientation correlation exists. The general relation between the scattered intensity and the structure of the fluid state, given in terms of the expansion functions of the pair correlation function and the expansion coefficients c of the scattering amplitude of the chain elements, is quite complex. 

Vibrational spectroscopy provides detailed infonnation on both structure and dynamics of molecular species. Infrared (IR) and Raman spectroscopy are the most connnonly used methods, and will be covered in detail in this chapter. There exist other methods to obtain vibrational spectra, but those are somewhat more specialized and used less often. They are discussed in other chapters, and include inelastic neutron scattering (INS), helium atom scattering, electron energy loss spectroscopy (EELS), photoelectron spectroscopy, among others. 

One of the most intriguing recent examples of disordered structure is in tomato bushy stunt virus (Harrison et ah, 1978), where at least 33 N-terminal residues from subunit types A and B, and probably an additional 50 or 60 N-terminal residues from all three subunit types (as judged from the molecular weight), project into the central cavity of the virus particle and are completely invisible in the electron density map, as is the RNA inside. Neutron scattering (Chauvin et ah, 1978) shows an inner shell of protein separated from the main coat by a 30-A shell containing mainly RNA. The most likely presumption is that the N-terminal arms interact with the RNA, probably in a quite definite local conformation, but that they are flexibly hinged and can take up many different orientations relative to the 180 subunits forming the outer shell of the virus particle. The disorder of the arms is a necessary condition for their specific interaction with the RNA, which cannot pack with the icosahedral symmetry of the protein coat subunits. 

Small angle X-ray scattering monitoring the distribution of electron density has been used to probe resin morphology [109]. More recently contrast matched small angle neutron scattering has also been employed [110, 111]. These techniques can also be applied to wet resins and tend to probe the very low dimensions of the polymer matrix structure. More studies are needed to identify the real value of these approaches. 

Gerchman, S.E. and Ramakrishnan, V. (1987) Chromatin higher-order structure studied by neutron scattering and scanning transmission electron microscopy. Proc. Natl. Acad. Sci. USA 84,... 

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