Proton spin-lattice relaxation in solutions of hydrogen chloride and deuterium chloride

Abstract

Proton spin-lattice relaxation times T1 for anhydrous solutions of hydrogen chloride and deuterium chloride have been measured at 20.8 Mc/s by a 90°-τ-90° pulse method. The measurements have been made, for most solutions, from the supercooled liquid (-116 °c) up to the liquid-vapour critical temperature (51.4 °c) and a little above. These T1 results for the HCl-DCl liquid solutions have provided direct evidence of the significant part played by the spinrotation interaction mechanism of relaxation in liquid HCl and have allowed a detailed analysis. The correlation times for the dipole-dipole intramolecular interaction τd and the spin-rotation interaction τsr have been determined independently and shown to vary in the opposite way with temperature. The product τdτsr was found to be almost independent of temperature and approximately six times greater than a theoretical value for spherical molecules given by Hubbard. It is suggested that τd and τsr are approximately equal at the critical temperature. The use of viscosity data is remarkably successful in the interpretation of molecular motion in this liquid for which the mean rotational quantum number is quite low. Two new contributions to relaxation, inter spin-rotation interactions, are evaluated approximately but they are probably negligible in liquid HCl.