Transport cross-sections for polyatomic gases

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Abstract
The paper considers the current status of the study of the transport and related effective cross-sections, for dilute molecular gases, that emerge from the kinetic theory as a unifying formulation of a number of diverse phenomena. The discussion concentrates upon the effective cross-sections that occur in the description of transport and relaxation phenomena in dilute gases and gas mixtures both in the absence of magnetic or electric fields and in their presence. The relationships of these phenomena to others such as light scattering, nuclear magnetic resonance relaxation and spectroscopic phenomena through effective cross-sections is illustrated. It is argued that, in general, experimental information on the effective cross-sections is either abundant or could be made so with little technological development and an investment only in time and effort. Equally the kinetic theory of dilute polyatomic gases is now both developed and secure. Thus the stage has been set for the application of the development of new methods of evaluating the effective cross-sections from prescribed intermolecular potentials that has characterised the last decade. These particular developments are reviewed in some detail to establish a set of guidelines for their application. While the guidelines are based on a limited set of studies they indicate the most fruitful paths for further progress towards the goal of understanding the role of particular molecular collisions in determination of specific observables which is otherwise concealed by the complicated averaging processes of the kinetic theory of gases.