Deuteron magnetic resonance probe of the D2–He potential energy surface

Abstract

Measurements of the nuclear magnetic resonance (NMR) longitudinal relaxation time T1 have been carried out for D2–He gas mixtures at temperatures of 293 and 220 K for two concentrations of D2 in He and the results extrapolated linearly to infinite dilution at each temperature. Full quantum close-coupled scattering calculations have also been carried out for an ab initio D2–He interaction potential. The agreement found between measured and calculated relaxation times is excellent at 293 and good at 220 K. Based on the level of agreement found between theory and experiment, it can be concluded that the molecular hydrogen–helium ab initio potential energy surface employed in the present D2–He calculations as well as in earlier H2–He calculations [J. Chem. Phys. 81, 5275 (1984)] represents well the effects of both the spin–rotation and combined dipolar/quadrupolar intramolecular interactions, which dominate the spin relaxation, respectively, of protons and deuterons in the hydrogen isotopes. At the same time, the present results indicate that the disagreement found earlier [J. Chem. Phys. 92, 5907 (1990)] between calculated and measured deuteron T1 values for HD–He mixtures must arise from the specific nature of the HD–He potential energy surface.