Towards a hydrogen economy: the microscopic structure of liquid hydrogen

In order to "see" what is infinitely small, man uses "eyes" that are made
of electron, X-ray, or neutron beams. The use of neutrons, essential in
some cases, has gained an increased importance in the last decades, and
the role played by neutron spectroscopy is clearly summarised in the
motivation of the 1994 Physics Nobel Prize awarded to two pioneers of this
technique, Shull from USA and Brockhouse from Canada, for having helped
to "understand where the atoms are and what the atoms do". Neutrons,
therefore, provide us with the possibility of knowing the mutual position
and dynamics of atoms, that is an essential piece of information to
explain, on a microscopic ground, the properties of matter at the
macroscopic scale. Hydrogen, which becomes liquid at very low temperature
(around -250 °C) is of great importance for both fundamental science and
technological applications. Indeed, in the last few years, it has
attracted the attention not only of scientists but also of politicians and
of the world public opinion: to quote only one example, it is sufficient
to mention the possible use of hydrogen as a clean fuel for vehicles. In a
next-future hydrogen economy, storage, transportation, and distribution of
large amounts of hydrogen will become hot topics. Among the various
techniques that are proposed for an effective storage and transportation,
liquid hydrogen represents one of the possible options. However, modelling
hydrogen's liquid phase is still an open problem. As a matter of fact,
this is a quantum liquid and several features are still not fully
understood, both from the theoretical and the experimental point of view.
It is a fact, that inconsistent results still appear in the scientific
literature. In this particular case, the use of neutrons, and the
expertise developed at IFAC in the study of quantum liquids, contributed
to a significant advance towards the solution of the problem. For the
first time, indeed, the microscopic structure of liquid hydrogen has been
determined using neutron scattering. Moving from this result, it will
become possible to extend the investigation to more complex topics, like
the microscopic dynamics and the hydrodynamic modelling of liquid
hydrogen, so far not adequately described on theoretical grounds, nor
obtainable from computer simulation techniques. It is worthwhile to
underline that, in this occasion, the role of the Public Research Bodies
turned out of fundamental importance. In fact, owing to the open-mind
attitude of CNR, first, and then of INFM, the scientific Italian
community, though deprived of national neutron sources, has been allowed
to gain access to the main European neutron facilities thanks to the
endorsement of international cooperation agreements.