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== Introduction ==
Diffraction occurs because the [[wavelength]] of electrons accelerated by a potential of a few thousand volts is of the same order of magnitude as internuclear distances in molecules. The principle is the same as that of other electron diffraction methods such as [[Low-energy electron diffraction|LEED]] and [[RHEED]], but the obtainable diffraction pattern is considerably weaker than those of LEED and RHEED because the density of the target is about one thousand times smaller. Since the orientation of the target molecules relative to the electron beams is random, the internuclear distance information obtained is one-dimensional. Thus only relatively simple molecules can be completely structurally characterized by electron diffraction in the gas phase. It is possible to combine information obtained from other sources, such as [[rotational spectroscopy|rotational spectra]], [[Nuclear magnetic resonance spectroscopy|NMR spectroscopy]] or high-quality quantum-mechanical calculations with electron diffraction data, if the latter are not sufficient to determine the molecule's structure completely.
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Some selected examples of important contributions to the [[structural chemistry]] of molecules are provided here:
* Structure of [[diborane]] B<sub>2</sub>H<sub>6</sub><ref>{{Cite journal|last=Hedberg|first=Kenneth|last2=Schomaker|first2=Verner|date=April 1951
* Structure of the planar trisilylamine<ref>{{Cite journal|last=Hedberg|first=Kenneth|date=1955-12-01|title=The Molecular Structure of Trisilylamine (SiH3)3N1,2|url=https://doi.org/10.1021/ja01629a015|journal=Journal of the American Chemical Society|volume=77|issue=24|pages=6491–6492|doi=10.1021/ja01629a015|issn=0002-7863}}</ref>
* Determinations of the structures of gaseous elemental [[phosphorus]] P<sub>4</sub> and of the binary P<sub>3</sub>As<ref>{{Cite journal|last=Cossairt|first=Brandi M.|last2=Cummins|first2=Christopher C.|last3=Head|first3=Ashley R.|last4=Lichtenberger|first4=Dennis L.|last5=Berger|first5=Raphael J. F.|last6=Hayes|first6=Stuart A.|last7=Mitzel|first7=Norbert W.|last8=Wu|first8=Gang|date=2010-06-23|title=On the Molecular and Electronic Structures of AsP3 and P4|url=https://doi.org/10.1021/ja102580d|journal=Journal of the American Chemical Society|volume=132|issue=24|pages=8459–8465|doi=10.1021/ja102580d|issn=0002-7863}}</ref>
* Determination of the structure of [[Buckminsterfullerene|C<sub>60</sub>]]<ref>{{Cite journal|last=Hedberg|first=K.|last2=Hedberg|first2=L.|last3=Bethune|first3=D. S.|last4=Brown|first4=C. A.|last5=Dorn|first5=H. C.|last6=Johnson|first6=R. D.|last7=De Vries|first7=M.|date=1991-10-18|title=Bond Lengths in Free Molecules of Buckminsterfullerene, C60, from Gas-Phase Electron Diffraction|url=https://www.sciencemag.org/lookup/doi/10.1126/science.254.5030.410|journal=Science|language=en|volume=254|issue=5030|pages=410–412|doi=10.1126/science.254.5030.410|issn=0036-8075}}</ref> and C<sub>70</sub><ref>{{Cite journal|last=Hedberg|first=Kenneth|last2=Hedberg|first2=Lise|last3=Bühl|first3=Michael|last4=Bethune|first4=Donald S.|last5=Brown|first5=C. A.|last6=Johnson|first6=Robert D.|date=1997-06-01|title=Molecular Structure of Free Molecules of the Fullerene C70 from Gas-Phase Electron Diffraction|url=https://doi.org/10.1021/ja970110e|journal=Journal of the American Chemical Society|volume=119|issue=23|pages=5314–5320|doi=10.1021/ja970110e|issn=0002-7863}}</ref>
* Structure of [[tetranitromethane]]<ref>{{Cite journal|last=Vishnevskiy|first=Yury V.|last2=Tikhonov|first2=Denis S.|last3=Schwabedissen|first3=Jan|last4=Stammler|first4=Hans-Georg|last5=Moll|first5=Richard|last6=Krumm|first6=Burkhard|last7=Klapötke|first7=Thomas M.|last8=Mitzel|first8=Norbert W.|date=2017-08-01|title=Tetranitromethane: A Nightmare of Molecular Flexibility in the Gaseous and Solid States|url=http://doi.wiley.com/10.1002/anie.201704396|journal=Angewandte Chemie International Edition|language=en|volume=56|issue=32|pages=9619–9623|doi=10.1002/anie.201704396}}</ref>
* Absence of local C<sub>3</sub> symmetry in the simplest [[phosphonium ylide]] H<sub>2</sub>C=PMe<sub>3</sub><ref>{{Cite journal|last=Mitzel|first=Norbert W.|last2=Brown|first2=Daniel H.|last3=Parsons|first3=Simon|last4=Brain|first4=Paul T.|last5=Pulham|first5=Colin R.|last6=Rankin|first6=David W. H.|date=1998|title=Differences Between Gas-Phase and Solid-State Molecular Structures of the Simplest Phosphonium Ylide, Me3P=CH2|url=https://onlinelibrary.wiley.com/doi/abs/10.1002/%28SICI%291521-3773%2819980703%2937%3A12%3C1670%3A%3AAID-ANIE1670%3E3.0.CO%3B2-S|journal=Angewandte Chemie International Edition|language=en|volume=37|issue=12|pages=1670–1672|doi=10.1002/(SICI)1521-3773(19980703)37:123.0.CO;2-S|issn=1521-3773}}</ref> and in [[Aminophosphine|amino-phosphanes]] like P(NMe<sub>2)3</sub> and [[
* Determination of intramolecular [[London dispersion force|London dispersion]] interaction effects on gas-phase and solid-state structures of diamondoid dimers<ref>{{Cite journal|last=Fokin|first=Andrey A.|last2=Zhuk|first2=Tatyana S.|last3=Blomeyer|first3=Sebastian|last4=Pérez|first4=Cristóbal|last5=Chernish|first5=Lesya V.|last6=Pashenko|first6=Alexander E.|last7=Antony|first7=Jens|last8=Vishnevskiy|first8=Yury V.|last9=Berger|first9=Raphael J. F.|last10=Grimme|first10=Stefan|last11=Logemann|first11=Christian|date=2017-11-22|title=Intramolecular London Dispersion Interaction Effects on Gas-Phase and Solid-State Structures of Diamondoid Dimers|url=https://doi.org/10.1021/jacs.7b07884|journal=Journal of the American Chemical Society|volume=139|issue=46|pages=16696–16707|doi=10.1021/jacs.7b07884|issn=0002-7863}}</ref>
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