Structure and Single Proton Dynamics of Bulk Supercooled Water

Neutron diffraction measurements with isotopic substitution (NDIS) and Deep In- elastic Neutron Scattering (DINS) experiments have been performed on bulk liquid water in the supercooled regime. Supercooling of ultra-pure water has been obtained thanks to a PTFE coating of the sample container. From the structural point of view the effect of supercooling at ambient pressure results in a slight change of the water coordination shells with respect to the structure of ambient water, although similarities with Low Density Water can be observed. As a matter of fact, the present data compare well with previous results obtained at about the same temperature, applying external pressure and can be interpreted within the second critical point scenario. DINS measurements have been carried out on this system with the aim of determining the anharmonic character of the momentum distribution of the protons, complementing the structural information on supercooled bulk water.