Comparative NMR Properties of H₂ and HD in Toluene-d₈ and in H₂/HD@C₆₀

Spin−lattice relaxation times, T₁, have been measured from 200−340 K for the protons in H₂ and HD molecules dissolved in toluene-d₈ and incarcerated in C₆₀. It is found that HD relaxes more slowly than H₂ in both environments and at all temperatures, as expected from the smaller values of the spin-rotation and dipole−dipole coupling in HD compared to H₂. More detailed analysis using models developed to describe relaxation in both condensed media and the gas phase indicates that transitions among the rotational states of H₂ occur at a rate similar to those of HD in both toluene-d₈ solution and in C₆₀, in contrast to the situation in gas phase collisions between hydrogen and He or Ar, where the lifetimes of rotational states of HD are markedly shorter than those for H₂. Measurements of the relative ¹H chemical shifts of H₂ and HD, the coupling constant J_HD, and the widths of the HD peaks at various temperatures revealed only small effects with insufficient accuracy to warrant more detailed interpretation.