On the Microscopic Structure of Liquid Hydrogens

Abstract

Among the quantum liquids, the hydrogens cover an interesting position between liquid helium, where quantum exchange gives rise to the macroscopic phenomenon of superfluidity, and neon, where quantum effects are relatively small, so that its features can be evaluated by perturbation methods with reference to a classical system. Nonetheless, the experimental access to the microscopic structure of the hydrogens is not an easy task both because of their intra-molecular structure and the small molecular mass that is comparable with that of the neutron probe. In this paper we discuss the state of the art and summarise the available experimental information on the microscopic structure of the hydrogens. The experimental data for the two systems are compared among them and with the results of quantum Path Integral Monte Carlo simulations. It is found that similar quantities, measured in corresponding thermodynamic points, are rather different for the two systems due to the different weight of quantum effects. Moreover, the comparison with the simulation results shows that, for deuterium, there is a substantial agreement, both at the level of the structure factor and its thermodynamic derivatives. The agreement is less satisfactory for liquid hydrogen.

Microscopic structure factor of liquid hydrogen by neutron-diffraction measurements

“…The first successful attempt to obtain structural information on liquid hydrogen, carried out on SANDALS, allowed us to determine the thermodynamic derivatives of S(k) [7]. These were found in a rather good quantitative agreement with the PIMC simulation results [8].…”

Microscopic structure of liquid hydrogen

“…Thus, a different way of extending the range of g(r ) had to be devised in order to circumvent Here, the open circles represent the SANDALS experimental data from [45] while the dots are the D4 data from [51]. The PIMC simulation results are taken from [58]. In the lower figure (liquid deuterium), the dots are the experimental point and the line represents the PIMC results.…”

“…Again, the deuterium experimental data (lower figure) appear Here, the open circles represent the SANDALS experimental data from [45]. The PIMC simulation results are taken from [58]. The deuterium data are reported in the lower figure . Here the experimental and simulation data are taken from [44].…”

The microscopic structure of the hydrogen liquids

“…The present hydrogen experiment was carried out at several thermodynamic points, thus allowing us to determine the density derivative of the structure factor. This quantity was also measured in a previous independent experiment [4] and the two results are compared in figure 2, together with the results of the PIMC simulations taken from [27]. The data appear rather noisy and not fully consistent in the low Q-region, even though the overall agreement among the three sets of data is satisfactory.…”

“…The density derivative, at constant temperature, of the structure factor of liquid hydrogen.The full circles represent the D4C experimental results[14], while the open triangles relate to the SANDALS experiment reported in[4]. The PIMC results (full curve) are taken from[27]. The full dot at Q = 0 is obtained from the thermodynamic compressibility.…”