Carbon-13 NMR of carbon monoxide. II. Molecular diffusion and spin–rotation interaction in liquid CO

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Abstract
Carbon‐13 NMR was used to measure the molecular diffusion coefficient D and the spin‐rotation correlation time τsr in liquid CO from its freezing point to about 110 K at several pressures up to 1.73 kbar. The behavior of D and τsr is similar for liquid CO and N2. Diffusion in CO at equilibrium vapor pressure takes place with an activation enthalpy of 2.9 kJ/mole and its pressure dependence leads to an activation volume which is a factor of 5 smaller than in the solid phase just below freezing. τsr is nearly equal for CO and N2 at T?80 K and its variation with pressure for CO is smaller than that of D by almost a factor of 2. We also present a method for determining the magnetic field gradient used in the measurement of D which is free from many of the usual problems.