Properties Of Parahydrogen Research Articles

The Scattering Properties of Gaseous Parahydrogen

In this work, the scattering properties of parahydrogen gas (p-H2) are studied in the temperature-range (1–50) K. These properties are investigated within the framework of the Lippmann–Schwinger formalism for p-H2. This formalism is used to calculate the phase shifts. The calculations are undertaken using Silvera-Goldman potential. The scattering properties of the system—the total, viscosity, and average cross sections—are then computed using these phase shifts. The s-wave scattering length for p-H2 molecules $$a_{o}$$ is determined as $$a_{o}$$ = 7.01 A. The cross sections exhibited the Ramsauer–Townsend effect and resonance peaks. The lifetime of the quasi-bound states for $$\ell - wave$$ $$\left( {\ell = {2,}\,{\text{4, and 6}}} \right)$$ is also computed.

Solidification of Hydrogen Clusters

The solidification of small parahydrogen clusters is studied. In such aggregates, where according to some Authors superfluid properties may be present, the principal antagonist of superfluidity is solidification. In this paper we investigate under what conditions solidification either cannot occur at all, or would occur only in times much longer than the lifetime of the cluster. Due to surface melting effects (enhanced by the van der Waals forces) the exterior layers of the cluster do not solidify. As far as the inner core is concerned, the solidification times depend notoriously strongly on the exact values of the parameters; they also depend strongly on the thickness of the molten layer. Nucleation implies a barrier, which in principle can be overcome either by thermal fluctuations (at relatively high temperatures) or by tunneling (at very low temperatures). Although a better knowledge of the physical properties of parahydrogen (especially the solid–liquid interface energy and the chemical potential of the two phases) is required, we confirm that in both cases the nucleation times can be exceedingly long.

A consistent spherical potential function for para-hydrogen

Several potential functions have recently been proposed to fit physical properties of hydrogen. We have calculated phase shifts for five of these functions and obtained second virials, bound state energy differences, and total and differential scattering cross sections to compare to the experimental data. We find that none of the previously proposed potentials can represent more than two of the above properties of para-hydrogen. Using the Hartree–Fock dispersion form proposed by Ahlrich et al., but changing the damping constant D from 1.28 to 1.31, a consistent representation is found for all the data except the differential scattering data. To fit the differential scattering data, the collision energy used in the calculation must be 3% larger than the stated value. This difference is within the experimental uncertainty of the differential scattering experiment.