  We are interested in dynamics of a system in an environment, or an open
system. Such phenomena like {\it crossover} from Markovian to non-Markovian
relaxation and {\it thermal equilibration} are of our interest. Open systems
have experimentally been studied with ultra cold atoms, ions in traps, optics,
and cold electric circuits because well isolated systems can be prepared here
and thus the effects of environments can be controlled. We point out that some
molecules solved in isotropic liquid are well isolated and thus they can also
be employed for studying open systems in Nuclear Magnetic Resonance (NMR)
experiments. First, we provide a short review on related phenomena of open
systems that helps readers to understand our motivation. We, then, present two
experiments as examples of our approach with molecules in isotropic liquids.
Crossover from Markovian to non-Markovian relaxation was realized in one NMR
experiment, while relaxation like phenomena were observed in approximately
isolated systems in the other.
