The Stochastic Liouville Equation and the Approach to Thermal Equilibrium

Abstract

Some aspects of behaviour of spins in the presence of random molecular motions are discussed. Various theories which deal with the approach of the spin system to thermal equilibrium are reviewed. It is emphasized that two types of description are used One is the ’p(t) formalism’, where the spin behaviour of one randomly moving molecule is considered. The other is the p(Ω) formalism’, where the average behaviour of all the spins which are momentarily in the same environment is described. The conventional relaxation theories make use of the p(t) formalism, whereas the Stochastic Liouville method for line shape calculations uses the p(Q) formalism. In the first type the approach to equilibrium has been dealt with for a long time. In the second type the approach to the thermal equilibrium state of p(Ω) was formulated only recently in the form of the modified stochastic Liouville equation. It is pointed out that this equation has important implications for both line shape calculations and for relaxation theory. © 1974, Walter de Gruyter. All rights reserved.