NUCLEAR MAGNETIC RESONANCE MEASUREMENTS IN HYDROGEN GAS

Abstract

The proton spin–lattice relaxation time T1 has been measured for H2 gas using pulse techniques over the temperature range 39 °K to 300 °K and at pressures up to 150 atmospheres. T1 is proportional to density, ρ, at low densities and constant temperature, over the entire temperature range studied. Deviations from linearity due to three-body collisions are observed at densities of the order of 500 Amagats. T1/ρ for the dilute gas is approximately constant from about 100 °K to 300 °K but increases sharply at lower temperatures. The spin–spin relaxation time T2 was measured at 78 °K and found to be proportional to ρ but shorter than T1. The diffusion constant D was measured, using the properties of the spin echo, at 78 °K in the dilute gas. Dρ was found to be constant. An analysis of the temperature dependence of T1/ρ using the theory of Needler and Opechowski shows that the excited rotational states of ortho-H2 probably play no role in the spin–lattice relaxation below 300 °K. The T1 results are interpreted in terms of the theory of Oppenheim and Bloom to give information on the anisotropic H2–H2 interactions. The constancy of T1/ρ at high temperatures cannot be understood in terms of the classical properties of the gas. Quantum mechanical diffraction effects play an extremely important role in the spin–lattice relaxation even at high temperatures because of the very short range nature of the anisotropic interactions.