Abstract
The incoherent neutron scattering law is derived for a proton which belongs to a XH4‐tetrahedron. Reorientations around threefold and twofold tetrahedral axes are taken into account. The latter process depends on the position of the neighboring tetrahedra. As a consequence the correlation time for the protonic motion is a function of the equilibrium pair correlation. In case of a first order phase transition this collective effect leads to a discontinuous change of the width of the quasielastic line.