A combined INS and DINS study of proton quantum dynamics of ice and water across the triple point and in the supercritical phase

We report new results of a combined analysis of previous Inelastic Neutron Scattering (INS) and Deep Inelastic Neutron Scattering (DINS) experiments on ice at T = 271 K and water at T = 285 K and T = 673 K. Proton quantum dynamics is discussed in terms of the total mean kinetic energy, 〈EK〉, and its three principal direction components, 〈EK〉α (with α=x,y,z), the lineshape momentum distribution, n(p), and its harmonic lineshape components, nh(p). The results show that the single proton dynamics is ground-state dominated and that 〈EK〉x,〈EK〉y and 〈EK〉z consist mainly of weighted averages of a mix of bending and librational, librational and stretching mean kinetic energy components, respectively. The stretching component 〈EK〉z is redshifted respect to its harmonic component due to additional network mode contributions and softening caused by anharmonicity. The n(p) lineshapes derived at the investigated temperature reflect the anisotropy and quasi-harmonic nature of proton motion in ice and water.