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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.
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}}</ref> The total scattering intensity is composed of two parts: the
[[File:GED C6H6 diff pattern.jpg|thumb|Figure 2: Diffraction pattern of gaseous benzene]]
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