Spin–Lattice Relaxation and the Anisotropic Part of the He–H2 Intermolecular Potential

The spin–lattice time $T_1$ of gaseous mixtures of H₂ and He has been measured as a function of composition and of temperature in the range 77°–300°K at pressures such that $T_1$ is proportional to the density. The relationship between the experimental $T_1$ and cross sections for molecular reorientation of H₂ is given. From comparison of computed cross sections to the data, experimental values are obtained for parameters in an approximate form for the He–H₂ anisotropic intermolecular potential.