Follow the water: an insight into proton quantum dynamics of selected phases of water by inelastic neutron scattering

The present PhD thesis stems from 36 months of intensive experimental investigation and data analysis of quantum dynamics of the hydrogen nucleus in various amorphous solid states (AIs) and supercritical phase (SCW) of water by inelastic neutron scattering. This doctoral effort places this work into the apparently inexhaustible stream of studies on water, at the same time offering an evidence of the role of density in shapingthesingle-particlepotential-energysurfaceintermsofcurvatureandanharmonicity,ashighlightedbyarecenthigh-impactpublicationinJ. Phys. Chem. Lett. [1]. The layout of the monograph has been thought for a broad audience, with an eye to making it both agile and exhaustive. After a brief introduction on the why and how of water and neutron spectroscopy, two separate chapters are dedicated to the properties of amorphous ices and the supercritical fluid, followed by the presentation of the fundamentals of inelastic (INS) and deep-inelastic (DINS) neutron techniques, and a sketch of the instrumentation employed, which is functional to the full understanding of the development of data reduction and analysis. Thesubsequentchapteronthepotentialofmeanforce(PMF)introducesanalternativeandpossiblyeasier-to-managewaytointerpretDINSoutputs. Thearrangement of related data and their interpretation into a scientific paper for a special issue of Front. Phys. is currently afoot. The work closes with a clean report of experimental results and relative discussion, which allows for inferring new insights into the function and effects of the H-bond environmentthemoleculesareimmersedin, aswellaspicturingfutureinvestigation scenarios. All INS and DINS experiments described in the following sections were performed at MARI and VESUVIO spectrometers, respectively, both located at ISIS Neutron and Muon Pulsed Source at the Rutherford Appleton Laboratory in the UK, with later data analysis and interpretation developed at the Department of Physics of Tor Vergata University of Rome, Italy. Theexperimentalworkwasaccompaniedbytheparticipationbypostercontribution in the 2013 International Conference on Neutron Scattering in Edinburgh, UK, the VI Workshop in eV Neutron Spectroscopy (2014) in Abingdon, UK, and the 2016 Erice School (’Water and Water Systems’) held in Erice (TP), Italy, and promoted by the School of Neutron Scattering (SoNS) entitled to Francesco Paolo Ricci.The second meeting called for my personal involvement into the coordination of the final scientific discussion, which is currently included in the proceedings of the conference [2–4]. A fruitful introduction to the PhD route was for sure the pre-doctorate course on general neutron scattering held by ILL in summer 2012 (Giornate Didattiche). As to present, I am about to start a full-immersion training as a McStas professional user, in order to participate in the development of the VESPA Project at the European Spallation Source (ESS). A parallel collaboration is in progress with a team based in Sapienza University of Rome in order to investigate anomalous transport properties of ultraconfined water by quasi-elastic neutron scattering (QENS) [5] and other spectroscopic techniques.