Combined translational-rotational jumps in solidα-CO

Combined translational-rotational jumps of CO molecules have been measured with the use of ${}_{}{}^{13}{}_{}{}^{}\mathrm{C}$ NMR in $\alpha$-CO solid. A molecule which jumps to a neighboring site in the $\mathrm{Pa}3\mathrm{}$ structure reorients because of the orientationally ordered nature of $\alpha$-CO. The reorientations were detected at high fields through the modulation of the chemical shift anisotropy; line narrowing, spin echoes, and stimulated echoes were used. The translational jumps modulated the dipolar interactions and were studied at low fields with line narrowing and $T_{1D}$ measurements. The rates of translations and rotations agree, confirming that they are two aspects of one motion. The rate of motion is described by the Arrhenius expression; the high prefactor of 2 × ${10}^{18}$ ${\mathrm{s}}^{-1\mathrm{}}$ is shown to be related to that seen in the similar solid ${\mathrm{N}}_2$O. The activation energy of 2100 K also agrees via corresponding states with that of ${\mathrm{N}}_2$O.