Zero-point motion of liquid and solid hydrogen

We present an inelastic neutron scattering study of liquid and solid hydrogen carried out using the wide Angu-lar Range Chopper Spectrometer at Oak Ridge National Laboratory. From the observed dynamic structure factor, we obtained empirical estimates of the molecular mean-squared displacement and average translational kinetic energy. We find that the former quantity increases with temperature, indicating that a combination of thermal and quantum effects is important near the liquid-solid phase transition, contrary to previous measurements. We also find that the kinetic energy drops dramatically on melting of the crystals, a consequence of the large increase in molar volume together with the Heisenberg indeterminacy principle. Our results are compared with quantum Monte Carlo simulations based on different model potentials. In general, there is good agreement between our findings and theoretical predictions based on the Silvera-Goldman and Buck potentials.

Automated summary

We conducted an inelastic neutron scattering study of liquid and solid hydrogen using the wide Angular Range Chopper Spectrometer at Oak Ridge National Laboratory. Our findings show that the molecular mean-squared displacement increases with temperature near the liquid-solid phase transition, indicating the importance of thermal and quantum effects. Additionally, we observed a significant drop in kinetic energy upon melting of the crystals, which can be explained by the large increase in molar volume and Heisenberg indeterminacy principle. The results were compared with quantum Monte Carlo simulations based on different model potentials, and good agreement was found with the Silvera-Goldman and Buck potentials.