Rotating frame NMR relaxation study of gaseous ClF

Publisher Website
Google Scholar
Abstract
This paper describes the first application of rotating frame NMR techniques to a gas phase system. Experiments were run on the linear diatomic molecule ClF at room temperature and various gas densities ranging from 13 to 28 amagat. By combining 19F rotating frame results with 19F spin–lattice relaxation timeT F 1 results, values of the chlorine spin–lattice relaxation timeT Cl 1 and the gas phase chlorine to fluorine spin–spin coupling constant J FCl were derived. Since ClF is a linear molecule, its relaxation times,T Cl 1 and T F 1 lead directly to values of the reorientational and angular velocity correlation times, τϑ,2 and τ J , respectively. The ratio τ J /τϑ,2 is found to be equal to 1.38±0.15, independent of gas density. This result is compared to various theories which relate τ J and τϑ,2, and it is shown that none of these theories adequately describe the gas phase reorientational motions of ClF. Rotating frame and spin–lattice relaxation timemeasurements were also made in the liquid and plastic crystalline solid phases of ClF. The reorientational correlation times derived from this data have an Arrhenius dependence on temperature with an activation energy of 1.2 kcal/mole. In addition, the analysis indicates that the liquid phase 19F to 35Cl spin–spin coupling constant J liq 35 is equal to 770±10 Hz; this is approximately 10% smaller than the 855±10 Hz determined for J gas 35 from the gas phase experiments.