From electron diffraction

Asbestos fiber identification can also be achieved through transmission or scanning electron microscopy (tern, sem) techniques which are especially usefiil with very short fibers, or with extremely small samples (see Microscopy). With appropriate peripheral instmmentation, these techniques can yield the elemental composition of the fibers using energy dispersive x-ray fluorescence, or the crystal stmcture from electron diffraction, selected area electron diffraction (saed). 

Structural parameters and interatomic distances derived from electron diffraction (7) (77JST(42)l2i) and X-ray diffraction (8) studies (76AX(B)3178) provide unequivocal evidence that pyrazine is planar with >2a symmetry. There is an increased localization of electron density in the carbon-nitrogen bonds, with carbon-carbon bonds being similar in length to those in benzene. ... 

TABLE 1. Bond lengths (rg) and bond angles (ra) of thionyl halides from electron diffraction... 

There is evidence from electron diffraction studies of pyrazine and pyridine that this value should be increased by 0.01 or 0.02 A because of the electronegativity of nitrogen (V. Schomaker and L. Pauling, paper to be published in Jour. Am. Chem. Soc.). 

The molecular structures from electron diffraction of zinc dichloride, zinc dibromide, and zinc diiodide have been reinvestigated.612 The important effects halides have on geometry have also been investigated, in particular the changes from octahedral to tetrahedral geometry in the presence of chloride ions have been studied.613... 

Bastiansen, O., Kveseth, K., and Mollendal, H. Structure of Molecules with Large Amplitude Motion as Determined from Electron-Diffraction Studies in the Gas Phase. 81, 99-172 (1979). 

Fig. 5.2 Radial distribution curves, Pv

Iijima, K., K. Tanaka, and S. Onuma. 1991. Main Conformer of Gaseous Glycine Molecular Structure and Rotational Barrier from Electron Diffraction Data and Rotational Constants. J. Mol. Struct. 246, 257-266. 

F. Vanhouteghem, W. Pyckhout, C. Van Alsenoy, L. Van den Enden, and H. J. Geise, The molecular structure of gaseous allyl alcohol determined from electron diffraction, microwave, infrared and geometry relaxed ab initio data. J. Mol. Struct. 140, 33 48 (1986). 

Fig. 5 a and b. The structure function (a) and pair correlation function (b) deduced from electron diffraction studies of D20 (Kalman and Palinkas, private communication)... 

We have reconstructed the 3D structure of a complex quasicrystal approximant v-AlCrFe (P6 m, a = 40.687 and c = 12.546 A) (Zou et al, 2004). Due to the huge unit cell, it was necessary to combine crystallographic data from 13 projections to resolve the atoms. Electron microscopy images containing both amplitude and phase information were combined with amplitudes from electron diffraction patterns. 124 of the 129 unique atoms (1176 in the unit cell) were found in the remarkably clean calculated potential maps. This investigation demonstrates that inorganic crystals of any complexity can be solved by electron crystallography. 

Symmetry determinations allow the identification of very important crystallographic features like the crystal system, the Bravais lattice and the point and space groups. Although it is usually performed from X-ray and neutron diffraction, symmetry determinations can also be obtained from electron diffraction. 

Thus, mosaic single crystal, polycristal, texture electron diffraction patterns provide valuable material for complete structural investigations. A complete determination of the unit cell of any crystal can be made from electron diffraction patterns, particularly of plate textures. 

An R-value of < 10% was obtained in case of brucite. This is quite accurate considering that the data comes from electron diffraction. 

XD Zou, Y Sukharev, S HovmdUer. ELD - a computer program system for extracting intensities from electron diffraction patterns. Ultramicroscopy 49 147-158,1993. 

SOLVING AND REFINING CRYSTAL STRUCTURES FROM ELECTRON DIFFRACTION DATA... 

The process of solving and refining crystal structures from electron diffraction data proceeds in a series of steps ... 

Not unlike X-ray crystallography, the following methods are used to solve crystal structures for small molecules from electron diffraction data ... 

Gautier, E., Tranqui, D., and Chaillout, C. (1997) First steps in the structure determination of an oxycarbonate superconductor from electron diffraction intensities. In Electron crystallography 375-378, edited by D.L. Dorset, S. HovmdUer and X. Zou NATO ASl series, 347. 

The Maximum Entropy Method of Solving Crystal Structures from Electron Diffraction Data... 

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