Kinetic Theory of Nuclear Magnetic Relaxation of Polyatomic Molecules

Abstract

Nuclear magnetic relaxation of polyatomic gases is discussed in terms of a Boltzmann equation. Weak intramolecular coupling is used to obtain formal expressions for the spin relaxation times and the chemical shift. In particular, restrictions arising from spin symmetry and from molecular point group symmetry are included.In carrying out the weak coupling calculation, it is necessary to approximate the time dependence of the rotational degrees of freedom. Here this is done with the aid of the 'rotating frame approximation', that is, all polarizations in the gas rotate in phase with the spins. This approximation is discussed from several points of view, including a mathematical discussion for a particular example. Finally the rotating frame approximation is related to the memory effects of general relaxation theory.