- Gas electron diffraction
Gas electron diffraction (GED) is one of the applications of
electron diffraction techniques. The target of this method is the determination of the structure ofgaseous molecules i.e. the geometrical arrangement of the atoms from which a molecule is built up.The geometrical structure of molecules can be worked out directly from the observed electron diffraction pattern by using this method. The principle is the same as that of other electron diffraction methods such as
LEED andRHEED , 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 and the orientation of the target relative to the electron beams is random, which corresponds to incoherent scattering.In the case of determining the structure of complex molecules, the information obtained from rotational
spectra is combined. The total scattering intensity is given as a function of themomentum transfer, which is defined as the difference between thewave vector of the incidentelectron beam and that of the scattered electron beam and has thereciprocal dimension oflength . The total scattering intensity is composed of two parts: theatomic scattering intensity andthe molecular scattering intensity . The former decreasesmonotonically and contains no information about the molecular structure. The latter hassinusoidal modulations as a result of theinterference of the scatteringspherical 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.
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