The Microscopic Structure of Hydrogens in the Liquid Phase

Liquid hydrogens are peculiar among quantum liquids. Their quantum properties are large enough that cannot be simply extrapolated, as in the case of neon, from the classical behavior using perturbation theory. However, their properties are not affected by quantum exchange, as in the case of helium, and Boltzmann statistics still applies. Thus, the microscopic structure of liquids composed by the hydrogen isotopes is mainly determined by the so-called quantum diffraction, i.e. from the delocalization of the molecular center-of-mass wave-functions. Using neutron diffraction, we have measured the thermodynamic derivatives of the structure factor of the two isotopes in the vicinity of the triple point. As expected, the results are not identical and some differences emerge. These can be mainly attributed to the molecular mass difference which reflects in the size of their respective quantum diffraction effect. Therefore, a quantitative comparison of the effect becomes extremely interesting.