Electron diffraction, by gases

V. P. Spiridonov, G. I. Mamaeva, Study of the Zirconium Borohydride Molecule by Electron Diffraction by Gases. Zh. Strukt. Khim. 1969, 10, 132-135. 

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. 

Planje MC, Toneman LH, Dallinga G (1965) Electron diffraction by gases - molecular structure of monochlorodimethyl ether. Rec Trav Chim 84 232-240... 

Sutton LE (1940) Electron diffraction by gases and vapours and electric dipole moments. Ann Rep Chem Soc 37 36-80... 

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. 

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. 

There is a rough parallel here with the method for making point atoms in electron diffraction by gases. Structure factors representing point atoms are the type of quantity normally used in phase-determining procedures. Instea(l of equation (21), we have... 

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. 

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],... 

The form of fi(Q) is analogous to the expression for elastic electron diffraction by molecular gases [31. 

The present article, which deals exclusively with electron diffraction in gases, does not pretend to give a complete survey or review of the field. The authors intention is, by a rather arbitrary choice of examples, mainly taken from the work done in Norway, to try to give an idea of what kind of problems we can hope to solve by the electron diffraction method. This, we hope, should be of greater value for those interested in the field of molecular structure than a more detailed theoretical introduction or a comprehensive review of all structure results obtained by electron diffraction during the last few years. 

The apparatuses used for the studies of both ammonia synthesis emd hydrodesulfurization were almost identical, consisting of a UHV chamber pumped by both ion and oil diffusion pumps to base pressures of 1 x10 " Torr. Each chamber was equipped with Low Energy Electron Diffraction optics used to determine the orientation of the surfaces and to ascertain that the surfaces were indeed well-ordered. The LEED optics doubled as retarding field analyzers used for Auger Electron Spectroscopy. In addition, each chamber was equipped with a UTI 100C quadrupole mass spectrometer used for analysis of background gases and for Thermal Desorption Spectroscopy studies. 

Electron diffraction studies have also provided structural information for chalcogen-nitrogen compounds that are liquids or gases at room temperature, e.g., the 1,2,3,5-dithiadiazolyl radical [CF3CNSSN] (3)22 and the 1,3,2-di-thiazolyl [CF3CSNSCCF3] (4).23 The structure of the trithiatriazine (NSF)3 (5) has also been determined in the gas phase by a combination of electron diffraction and microwave spectroscopy, which shows that all three fluorine atoms are axial.24... 

The basic modem data describing the atomic stmcture of matter have been obtained by the using of diffraction methods - X-ray, neutron and electron diffraction. All three radiations are used not only for the stmcture analysis of various natural and synthetic crystals - inorganic, metallic, organic, biological crystals but also for the analysis of other condensed states of matter - quasicrystals, incommensurate phases, and partly disordered system, namely, for high-molecular polymers, liquid crystals, amorphous substances and liquids, and isolated molecules in vapours or gases. This tremendous... 

It is of interest to attempt to cast the absorption-edge spectrum in a form resembling a diffraction function. In conventional diffraction of X-rays or electrons by gases, liquids, or crystals, the general diffraction function expresses the ratio of scattered intensity, 7 to incident intensity, 7o, as a function of (sin 0)/, where d is half the scattering angle ... 

Other diffraction methods include electron diffraction, which may be used to determine the structures of gases or of volatile liquid substances that cannot be obtained as crystals suitable for x-ray diffraction, and neutron diffraction, which has special application for crystals in which the exact location of hydrogens is desired. Hydrogen does not have sufficient scattering power for x rays to be located precisely by x-ray diffraction. 

Simple aUcah metal halide molecules, for example NaCl and KCl, are found in the vapors above heated samples of the solid compounds. These vapor species have been studied by IR spectroscopy of gases and matrices, and by gas electron diffraction. The studies show that planar rhombic dimers are also present. 

Electron Diffraction (Elektronenbeugung in Ger). Tt is the investigation of the structure of a surface of a substance by the diffraction (bending) of a stream of electrons directed upon it. Important differences between electron X-ray diffraction arise from the lower penetrating power of electrons. This means that electrons are much more sensitive to small amts of matter and are preferred over X-rays for studying gases surface films, which may be only a few atoms thick... 

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