Spin-Lattice Relaxation of Very Pure Solido−D2

Orthodeuterium of unprecedented purity $p-{\mathrm{D}}_2$ concentration $c_1=1.7\mathrm{}\times {10}^{-4\mathrm{}}$ has been produced, with spin-lattice relaxation time $T_1^{\mathrm{D}}\left({\mathrm{D}}_2\right)\simeq 0.5$ h at $T=4.2\mathrm{}$ K and $H=0.7\mathrm{}$ T. This suffices for retention of high spin polarization built up at millikelvin temperatures and use at 1-4 K as a highly spin-polarized $\uparrow {\mathrm{D}}_2$ solid. $T_1^{\mathrm{D}}\left({\mathrm{D}}_2\right)$ from 1 to 10 K and 0.01 to 0.70 T are compared with $T_1^{\mathrm{H}}\left(\mathrm{HD}\right)$ and $T_1^{\mathrm{D}}\left(\mathrm{HD}\right)$, allowing tests of current relaxation theories. Measurement of the $p-{\mathrm{D}}_2\to o-{\mathrm{D}}_2$ homogeneous conversion rate in ${\mathrm{D}}_2$ at 4.2 K for ${10}^{-4\mathrm{}}<c_1<{10}^{-3\mathrm{}}$ is found to be substantially in agreement with a previous determination for $0.20<\mathrm{}{c}_1<0.90\mathrm{}$.