Spin alignment of protons in NH4+at low temperatures

Abstract
In a neutron transmission experiment the authors have observed the intramolecular spin alignment of protons in NH4ClO4 at low temperatures. Changes in total scattering cross section are analysed in terms of coherent neutron scattering from the rotational states of protonated molecules, i.e. tunnelling of these molecules between different equilibrium orientations. The wavevector-dependent part of the coherent scattering is seen to follow earlier theoretical predictions rather closely.