Self-Diffusion of Liquid Deuterium Hydride and Liquid Tritium

Abstract

We present a quasi-elastic neutron scattering study of liquid deuterium hydride carried out using the Disk Chopper Spectrometer at the National Institute of Standards and Technology. Under saturated vapor pressure, the self-diffusion constant of deuterium hydride obeys an Arrhenius law D = D₀exp−E_A/k_BT⁠, where the prefactor <i>D₀ </i>is given by D₀= 9.5±1.2 Ų/ps and the activation energy is given by <i>E</i>_<i>A</i> = 58 ± 2 K. We apply the quantum law of corresponding states to the known diffusion constants of the hydrogen isotopologues. From this application, we estimate that D₀ ≈ 9.1 Ų/ps and <i>E</i>_<i>A</i> ≈ 75 K in liquid tritium. Young’s theory of quantum-mechanical effects in van der Waals fluids [Young, Phys. Rev. A <b>23</b>, 1498 (1981)] is shown to apply to the diffusion constants of the liquid hydrogens. Our results underscore the importance of nuclear quantum effects in shaping the properties and behavior of the hydrogen isotopologues.