Gas electron diffraction: Difference between revisions

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{{short description|Method of observing gaseous atomic structure}}

'''Gas electron diffraction''' (GED) is one of the applications of [[electron diffraction]] techniques.<ref name=":0">{{Cite book|last=Rankin, David W. H.|title=Structural methods in molecular inorganic chemistry|others=Morrison, Carole A., 1972-, Mitzel, Norbert W., 1966-|date=2 January 2013|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 determination of accurate molecular structures<ref>{{Cite book|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 is fundamental for an understanding of [[structural chemistry]].<ref>{{Cite book|last=Wells, A. F. (Alexander Frank), 1912-|title=Structural inorganic chemistry|date=12 July 2012|isbn=978-0-19-965763-6|edition=Fifth|___location=Oxford|oclc=801026482}}</ref><ref name=":0" />

'''Gas electron diffraction''' ('''GED''') is one of the applications of [[electron diffraction]] techniques.<ref name=":0">{{Cite book|last=Rankin, David W. H.|title=Structural methods in molecular inorganic chemistry|others=Morrison, Carole A., 1972-, Mitzel, Norbert W., 1966-|date=2 January 2013|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 determination of accurate molecular structures<ref>{{Cite book|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 is fundamental for an understanding of [[structural chemistry]].<ref>{{Cite book|last=Wells, A. F. (Alexander Frank), 1912-|title=Structural inorganic chemistry|date=12 July 2012|isbn=978-0-19-965763-6|edition=Fifth|___location=Oxford|oclc=801026482}}</ref><ref name=":0" />

== Introduction ==

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== Results ==

[[File:Examples P4 P3As.jpg|thumb|440x440px|Figure 5: Examples of molecular intensity curves (left) and their Fourier transforms, the radial distribution curves of P4 and P3As.]]

Figure 5 shows two typical examples of results. The molecular scattering intensity curves are used to refine a structural model by means of a [[Least-squares function approximation|least squares]] fitting [http://unexprog.org/ program]. This yieldyields precise structural information. The [[Fourier transformation]] of the molecular scattering intensity curves gives the radial distribution curves (RDC). These represent the probability to find a certain distance between two nuclei of a molecule. The curves below the RDC represent the diffrerencedifference between the experiment and the model, i.e. the quality of fit.

The very simple example in Figure 5 shows the results for evaporated white [[phosphorus]], P₄., Itwhich is a perfectly tetrahedral molecule and has thus only one P-P distance. This makes the molecular scattering intensity curve a very simple one; a sine curve which is damped due to molecular vibration. The radial distribution curve (RDC) shows a maximum at 2.1994 Å with a least-squares error of 0.0003 Å, represented as 2.1994(3) Å. The width of the peak represents the molecular vibration and is the result of [[Fourier transform]]ation of the damping part. This peak width means that the P-P distance varies by this vibration within a certain range given as a vibrational amplitude ''u'', in this example ''u''_T(P‒P) = 0.0560(5) Å.

The slightly more complicated molecule P₃As has two different distances P-P and P-As. Because their contributions overlap in the RDC, the peak is broader (also seen in a more rapid damping in the molecular scattering). The determination of these two independent parameters is more difficult and results in less precise parameter values than for P₄.

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* 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|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]] P₄ and of the binary P₃As<ref>{{Cite journal|last1=Cossairt|first1=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|journal=Journal of the American Chemical Society|volume=132|issue=24|pages=8459–8465|doi=10.1021/ja102580d|pmid=20515032|issn=0002-7863}}</ref>

* Determination of the structure of [[Buckminsterfullerene|C₆₀]]<ref>{{Cite journal|last1=Hedberg|first1=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|journal=Science|language=en|volume=254|issue=5030|pages=410–412|doi=10.1126/science.254.5030.410|pmid=17742230|bibcode=1991Sci...254..410H |s2cid=25860557|issn=0036-8075}}</ref> and C₇₀<ref>{{Cite journal|last1=Hedberg|first1=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|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|last1=Vishnevskiy|first1=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|journal=Angewandte Chemie International Edition|language=en|volume=56|issue=32|pages=9619–9623|doi=10.1002/anie.201704396|pmid=28557111|doi-access=free}}</ref>

* Absence of local C₃ symmetry in the simplest [[phosphonium ylide]] H₂C=PMe₃<ref>{{Cite journal|last1=Mitzel|first1=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)37:12<1670::AID-ANIE1670>3.0.CO;2-S|pmid=29711513|issn=1521-3773|url-access=subscription}}</ref> and in [[Aminophosphine|amino-phosphanes]] like P(NMe₂₎₃ and [[ylide]]s H₂C=P(NMe₂)₃<ref>{{Cite journal|last1=Mitzel|first1=Norbert W.|last2=Smart|first2=Bruce A.|last3=Dreihäupl|first3=Karl-Heinz|last4=Rankin|first4=David W. H.|last5=Schmidbaur|first5=Hubert|date=January 1996|title=Low Symmetry in P(NR 2 ) 3 Skeletons and Related Fragments: An Inherent Phenomenon|journal=Journal of the American Chemical Society|language=en|volume=118|issue=50|pages=12673–12682|doi=10.1021/ja9621861|issn=0002-7863}}</ref>

* Determination of intramolecular [[London dispersion force|London dispersion]] interaction effects on gas-phase and solid-state structures of diamondoid dimers<ref>{{Cite journal|last1=Fokin|first1=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|journal=Journal of the American Chemical Society|volume=139|issue=46|pages=16696–16707|doi=10.1021/jacs.7b07884|pmid=29037036|issn=0002-7863}}</ref>

== Links ==

* http://molwiki.org/wiki/Main_Page—A{{Dead link|date=December 2022 |bot=InternetArchiveBot |fix-attempted=yes }} free encyclopaedia, mainly focused on molecular structure and dynamics.

* The story of gas-phase electron diffraction (GED) in [https://www.researchgate.net/publication/332484908_The_story_of_gas-phase_electron_diffraction_GED_in_Norway Norway] <ref>{{Cite journal|last=Kveseth|first=Kari|date=August 2019|title=The story of gas-phase electron diffraction (GED) in Norway|url=http://link.springer.com/10.1007/s11224-019-01309-w|journal=Structural Chemistry|language=en|volume=30|issue=4|pages=1505–1516|doi=10.1007/s11224-019-01309-w|s2cid=146084935 |issn=1040-0400|url-access=subscription}}</ref>

==References==