Low-temperature nuclear-spin relaxation times and line shapes for Hsub2 in solid nonmagnetic hosts.

Abstract

We calculate the nuclear-spin relaxation time ${T}_{1}$ and line-shape function for isolated ortho- (J=1) ${\mathrm{H}}_{2}$ molecules in solid nonmagnetic hosts located at sites with various crystal-field symmetries. This work includes modifications of earlier work so that the formalism can be used in regimes where ${\ensuremath{\Gamma}}_{m}$, the molecular angular momentum relaxation rate, is not large compared to the molecular-nuclear spin coupling constants ${\ensuremath{\omega}}_{c}$ and ${\ensuremath{\omega}}_{d}$. The formalism also allows for a nonzero value of the quadrupolarization 〈3${J}_{z}^{2}$-${J}^{2}$〉. With these changes the theory can be used at temperatures at and below about 4 K where line shapes evolve from Lorentzians into Pake doublets.