A theorem was derived for coherent quasi-elastic neutron scattering signals from a lattice of N molecules undergoing rotational jump diffusion. If no correlations existed between the molecular jumps, then the coherent quasi-elastic scattering signal was just N times that of a single molecule. The elastic contribution was simply the diffraction diagram of the system. This implied that there was no coherent elastic contribution between the Bragg peaks. That is, the coherent signal between the Bragg peaks was purely quasi-elastic. The results for coherent scattering were in sharp contrast to those for incoherent scattering, where one could also find elastic scattering outside of the Bragg peaks.

Coherent Quasi-Elastic Neutron Scattering: a Theorem about Total Neutron Scattering Functions for Rotational Jump Diffusion of Molecules on a Lattice. G.Coddens: Physical Review B, 2001, 63[6], 064105 (7pp)