Nuclear Spin-Relaxation in Other Aggregation States

This chapter deals with relaxation in the gas phase the conditions when the gas becomes more liquid-like. This will be followed by a brief presentation of relaxation in gases under moderate pressure and a short discussion of nuclear magnetic resonance (NMR) of ¹²⁹Xe. As one might expect, NMR relaxation in gases at high density displays a behaviour similar to that in liquids, which gives rise to interesting applications of supercritical fluids as solvents for NMR studies, as reviewed by Taylor and Jacobson in eMagRes. Relaxation studies under low and moderate gas pressure provide qualitatively different information than in the high-pressure region. The theory of nuclear spin-relaxation in liquid crystalline solutions differs in some important points from the case of isotropic liquids. The double-quantum relaxation rate depends only on the high-frequency spectral densities. The spin-relaxation properties in an anisotropic medium are dependent on the orientation of the medium with respect to the magnetic field.