Electron diffraction, in gases, and

Electron Diffraction in Gases and Molecular Structure (Bastiansen ... 

Widely used treatises and monographs on the theory and the applications of MRR-spectroscopy are available [8-//], also comprehensive reviews on all aspects of obtaining molecular structure from MRR-spectra [6,12,13], including rovib interactions [14] and the reliability of the results [15-17], Molecular structural and other data obtained from MRR spectroscopy have been compiled over the past decades [18,19], The most recent compilation is MOGADOC (short for Molecular Gas Phase Documentation ), a computerized database and retrieval system that is updated periodically and today contains more than 20,000 references, which were critically selected and evaluated by means of keywords. Included is work done by MRR-spectroscopy, electron diffraction of gases, and molecular radio astronomy the documentation refers to more than 6000 compounds. As an additional feature, MOGADOC contains explicit numerical data on the structure of approximately 2000 compounds. A detailed description can be found in ref. [20],... 

E.A.V. Ebsworth, D.W.H. Rankin and S. Cradock (1991) Structural Methods in Inorganic Chemistry, 2nd edn, CRC Press, Boca Raton, FL - A chapter on diffraction methods includes electron diffraction by gases and liquids. 

S. J. Cyvin "Molecular Vibrations and Mean Square Amplitudes", Amsterdam Elsevier, 1968. M. Davis "Electron Diffraction in Gases", New York Marcel Dekker, 1971. 

A subject emphasized in this article concerns the role of non-negativity in structural research in terms of its immediate applications, its special mathematical features and the use of additional probabilistic insights. The experimental techniques considered are electron diffraction by gases and X-ray diffraction by crystals. 

In this historical outline of some of the main contributions of mathematics to structural research in the areas of electron diffraction by gases and X-ray diffraction by crystals, it has been seen that these areas have benefited considerably by the application of mathematics. The same is true of other areas of structural research. It is also so that improvements in the mathematical techniques bode well for the future. In view of the broad implications of structural research to many fields of science, it may be said that structural research is an example of a discipline in which those who enjoy the application of mathematics to scientific problems can also enjoy the broad fruitfulness of the results. 

D. H. Whiffen, Biog. Mem. Roy. Soc., 1994, 40, 369 Sutton, The Earlier Studies in Great Britain of the Structure of Molecules in Gases and Vapours by Electron Diffraction, with an epilogue , in P. Goodman (ed), Fifty Years of Electron Diffraction , Reidel, Dordrecht, 1981, pp. 92-100 Sutton, account of life, Sutton Papers, A2, Bodleian Library. 

As we derived in Section 8.1.3, nX = 2d sin d. This is the Bragg equation, which states that coherence occurs when nX = 2d sin 9. It can be used to measure d, the distance between planes of electron density in crystals, and is the basis of X-ray crystallography, the determination of the crystal structure of solid crystalline materials. Liquids, gases, and solids such as glasses and amorphous polymers have no well-ordered structure therefore they do not exhibit diffraction of X-rays. 

L. S. Bartell, Electron Diffraction by Gases , in Physical Methods of Chemistry , ed. A. Weissberger and B. W. Rossiter, Wiley-Interscience, New York, 1972, Vol. 1, Part 3D, Chapter 2. 

Bartell, L.S. (I972) Electron Diffraction by Gases. Physical Methods in Organic ChemistiTy (ed Weissberger, A. and Eossiter, Interscience, New York. 

Electron diffraction studies provide valuable information about structures in the gas phase. Consequently, this method is important for chalcogen-nitrogen compounds that are liquids or gases at room temperature. The application of this technique has provided evidence for the monomeric structures of the 1,2,3,5-dithiadiazolyl radical [CEsCNSSN] (3.3) and the 1,3,2-dithiazolyl [CEsCSNSCCEs] (3.4), a... 

The distances between atoms in a molecule are characteristic properties of the molecule and can give us information if we compare the same bond in different molecules. The chief methods of determining bond distances and angles are X-ray diffraction (only for solids), electron diffraction (only for gases), and spectroscopic methods, especially microwave spectroscopy. The distance between the atoms of a bond is not constant, since the molecule is always vibrating the measurements obtained are therefore average values, so that different methods give different results. However, this must be taken into account only when fine distinctions are made. 

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