PROTON SPIN–LATTICE RELAXATION IN POLYATOMIC GASES

Abstract

The proton spin–lattice relaxation time T1 has been measured in gaseous samples of methane, ethylene, and ethane as a function of pressure at room temperature and also at 193° K for methane. In the pure gases T1 is proportional to density, p, at low densities indicating that intramolecular interactions couple the spin systems to the lattice, as is the case in hydrogen gas. T1/p at low densities gives information on the mean square angle through which the molecules are rotated per collision. Relaxation due to paramagnetic O2 is observed at higher densities when oxygen gas is added as an impurity. The relaxation probability per collision with an oxygen molecule is about 5 times larger for the ethylene–oxygen system than for the other two systems studied. This anomaly is discussed in terms of the theory of Oppenheim and Bloom. It is shown that a study of the temperature dependence of T1 due to O2 impurities provides a new way of obtaining detailed information on the Lennard–Jones parameters for the interaction between O2 and the solvent molecules.