ABSTRACT
We start with the following question: if experimental measurement of accurate structural parameters is required, why should we consider neutron diffraction?
There is a good, fundamental answer to this question - neutrons are scattered by atomic nuclei, and therefore reveal directly the positions and displacement amplitudes of the nuclei in a molecule. Since the coherent neutron scattering lengths, b, for the elements commonly encountered in organic molecules fall in a relatively narrow range, neutron diffraction is
very effective for determining the positions of 1 H-and 2H-atoms (b = -3.7406 and 6.671, respectively) in the presence of heavier atoms such as 12C (b = 6.6511), 14N (b = 9.37), 160 (b = 5.803) and 32S (b = 2.804) (b in units of 10-15 m; data taken from Sears (1992)).
