Gas electron diffraction: Difference between revisions

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'''Gas electron diffraction''' (GED) is one of the applications of [[electron diffraction]] techniques.<ref name=":0">{{Cite book|last=Rankin, David W. H.|url=https://www.worldcat.org/oclc/810442747|title=Structural methods in molecular inorganic chemistry|others=Morrison, Carole A., 1972-, Mitzel, Norbert W., 1966-|isbn=978-1-118-46288-1|___location=Chichester, West Sussex, United Kingdom|oclc=810442747}}</ref> The target of this method is the determination of the structure of [[gaseous molecules]] i.e. the [[Molecular geometry|geometrical arrangement of the atoms]] from which a molecule is built up. GED is one of two experimental methods (besides microwave spectroscopy) to determine the structure of free molecules, undistorted by intermolecular forces, which are omnipresent in the solid and liquid state. The detremination of accurate molecular structures<ref>{{Cite book|url=https://www.worldcat.org/oclc/26264763|title=Accurate molecular structures : their determination and importance|date=1992|publisher=International Union of Crystallography|others=Domenicano, Aldo., Hargittai, István.|isbn=0-19-855556-3|___location=[Chester, England]|oclc=26264763}}</ref> by GED studies are fundamental for a understanding of [[structural chemistry]].<ref>{{Cite book|last=Wells, A. F. (Alexander Frank), 1912-|url=https://www.worldcat.org/oclc/801026482|title=Structural inorganic chemistry|isbn=978-0-19-965763-6|edition=Fifth|___location=Oxford|oclc=801026482}}</ref><ref name=":0" />{{Multiple issues|

{{citation style|date=December 2018}}

{{one source|date=December 2018}}

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== Introduction ==

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The total scattering intensity in GED is given as a [[function (mathematics)|function]] of the [[momentum]] transfer, which is defined as the difference between the [[wave vector]] of the incident [[electron]] beam and that of the scattered electron beam and has the [[reciprocal dimension]] of [[length]].<ref name=":1">{{Cite book|last=Bonham|first=R.A.|title=High Energy Electron Scattering|publisher=Van Nostrand Reinhold|year=1974|isbn=|___location=|pages=}}</ref> The total scattering intensity is composed of two parts: the [[atomic scattering intensity]] and [[the molecular scattering intensity]]. The former decreases [[monotonically]] and contains no information about the molecular structure. The latter has [[sinusoidal]] modulations as a result of the [[Interference (wave propagation)|interference]] of the scattering [[spherical waves]] generated by the scattering from the atoms included in the target molecule. The interferences reflect the distributions of the atoms composing the molecules, so the molecular structure is determined from this part.

== Theory ==

== Theory<ref>{{Cite book|title=Stereochemical Applications of Gas‐Phase Electron Diffraction, Part A: The Electron Diffraction Technique|last=Hargittai|first=I.|publisher=VCH Verlagsgesellschaft|year=1988|___location=Weinheim|pages=}}. {{isbn|3-527-26691-7|0-89573-337-4}}</ref><ref name=":1" /> ==

GED can be described by scattering theory. The outcome if applied to gases with randomly oriented molecules is provided here in short:<ref>{{Cite book|title=Stereochemical Applications of Gas‐Phase Electron Diffraction, Part A: The Electron Diffraction Technique|last=Hargittai|first=I.|publisher=VCH Verlagsgesellschaft|year=1988|___location=Weinheim|pages=}}. {{isbn|3-527-26691-7|0-89573-337-4}}</ref><ref name=":1" />

Scattering occurs at each individual atom (<math> I_a(s)