Proton momentum distribution in solid and liquid HF

Abstract

Neutron Compton scattering (NCS) experiments were performed on liquid and solid HF, a system where the effective Born-Oppenheimer (BO) potential energy surface is not isotropic. Proton momentum distributions were calculated in the framework of the impulse approximation from measured neutron Compton profiles. A detailed data analysis shows that there are no systematic changes in the width, position of the maximum, or excess kurtosis of proton momentum distributions in both systems with increasing scattering angle. This observation has important implications for further theoretical work on violation of BO approximation in the presence of ultrafast neutron-proton scattering. That is, the picture of proton dynamics in HF emerging from the analysis of NCS data does not seem to support the previously considered model of protons accessing excited electronic states due to ultrafast scattering.