Nuclear Magnetic Relaxation in Hydrogen—Rare Gas Mixtures

Abstract

The proton spin lattice relaxation time (T₁) has been measured in binary mixtures of hydrogen and rare gases over the temperature range of 165–265°K and at densities of roughly 20 amagats and rare gas fractions of 0%‐60%. From this data the contribution to the proton T₁ from H₂—rare gas collisions was found by extrapolating the measurements to zero concentration of hydrogen. The data have been fit by coupled channel molecular scattering calculations, assuming infrequent transitions of the hydrogen molecule between rotational levels, and using a Lennard‐Jones (12, 6) potential for the isotropic and angular‐dependent parts of the intermolecular potential. The calculated thermally averaged reorientation cross sections can be represented in a way (suggested by the Bloom—Oppenheim theory) which makes clear the sensitivity of the various parameters of the potential to the data. The calculations indicate that the apparent anisotropy in the attractive part of the H₂—rare gas interaction is approximately twice as great as that predicted by molecular polarizability measurements; this is probably a consequence of choosing an oversimplified model for the potential. The Bloom—Oppenheim theory predicts much larger reorientation cross sections than does quantum scattering theory and yields values for the molecular anisotropy which are in approximate agreement with the polarizability data.