Proton and deuteron magnetic resonance study of the HD–He potential energy surface

Abstract

The relaxation of hydrogen and deuterium nuclei in HD–He gas mixtures is studied both experimentally and theoretically in the temperature range 90–300 K. A rationalization is given for the temperature dependence of the proton and the deuteron relaxations in terms of the relative strengths of the proton and deuteron intramolecular couplings and the role played by those HD molecules in the ground rotational state. Using a recent ab initio potential, quantitative agreement is found between the temperature dependence of the spin–lattice relaxation time of the proton in HD, as calculated theoretically and determined experimentally. A similar comparison between the calculated and experimental temperature dependence of the spin–lattice relaxation time of the deuteron in HD gave only semiquantitative agreement. It is suggested that the difference in quantitative agreement may be attributed to the selectivity of the respective predominant relaxation mechanisms to slightly different aspects of the anisotropic components of the interaction potential.