Nuclear Relaxation in Gases: Mixtures of Methane and Oxygen

Three previously proposed mechanisms of nuclear relaxation in fluids are qualitatively discussed: (1) modulation of intramolecular fields by collisions, (2) transient, and (3) diffusively modulated dipolar interactions with paramagnetic impurities. It is shown that the dependence of T1 for the protons in methaneoxygen mixtures on composition, density, and temperature is adequately described by a superposition of these contributions to 1/T1, and that the magnitudes involved are consistent with a priori estimates. It is suggested that the spin-rotation interaction provides an important relaxation mechanism in both gaseous and liquid methane.