ABSTRACT
Operator Formalism....................................................................................16 References ............................................................................................... 18
The concepts of equilibrium and deviation from equilibrium have a central role in physical chemistry. Once a system is in a nonequilibrium state, it will tend to return to equilibrium in a process which does not occur instantaneously. This general phenomenon of development towards equilibrium is called
relaxation
. In the specific context of nuclear magnetic resonance, the equilibrium state is that of a macroscopic sample of nuclear spins in a magnetic field. In order to talk about a development towards equilibrium, we need to define and be able to create an initial state, which is different from the equilibrium state.
