Proton and Deuteron Spin Relaxation in Hydrogen - - Helium Gas Mixtures.

Nuclear magnetic relaxation experiments have been performed on HD-He gas mixtures in order to obtain T _1/rho data of sufficient accuracy to provide a sensitive test of intermolecular potentials. Measurements of both the proton and deuteron magnetizations were made over a temperature range of 90 K to 295 K for two different dilutions of HD in He. At each temperature studied, the gas density dependence of the nuclear relaxation was measured over a density range of approximately 15 to 50 Amagat and then extrapolated to zero density to obtain a value due to binary collisions. The resulting values for the two different dilutions were then extrapolated to values representing infinite dilution of HD in He ((T_1/rho )|_sp{lin}{ infty}). These values are compared to those calculated from two different H_2-He intermolecular potentials that have been adapted to the HD-He system. The potentials are an empirical potential proposed by Shafer and Gordon (SG) and a fully ab initio potential proposed by Kohler and Shaefer (KS). It is seen that while the KS potential provides a quantitative fit to the previous H_2-He data, it provides a qualitative but not quantitative fit to the HD-He data, as does the SG potential. Various physical aspects of the data and theoretical calculations are discussed and possible explanations for the quantitative differences between the theory and data are brought forward along with possibilities for further study.