RELAXATION AND TRANSPORT OF MOLECULAR-SYSTEMS IN THE GAS-PHASE

Some of the properties of gas phase relaxation and transport are revie wed with an emphasis on those properties that are due entirely to the presence of internal states in real molecular systems. The theoretical formulations of such non-equilibrium effects is based on the quantum Boltzmann equation. The conditions for the validity and the properties of this equation are reviewed. This includes a general discussion of how the combination of free molecule motion and collisions is required for the approach to global equilibrium. It is shown how the free moti on is equivalent to a phase randomization of the elements of the densi ty operator that are off-diagonal in energy. Spin relaxation and the m agnetic held dependence (Senftleben-Beenakker effects) of the viscosit y for a gas of diatomics are used to illustrate these aspects of the a pproach to equilibrium.