Nonresonant Absorption and Spin Relaxation in Polyatomic Gases

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Abstract
A theory is developed for nonresonant dipolar absorption of microwaves and for spin‐relaxation times in polyatomic gases. Molecular reorientation produced by independent binary collisions results in nonresonant absorption of the Debye shape. The correlated effects of two, three, etc., successive binary collisions produce corrections to the Debye form. These correlations are present because the amount of angular momentum transferred by a given collision depends on the initial rotational state, which in turn is determined by previous collisions. Keeping only correlations through two collisions gives a good account of the pressure and frequency dependence of nonresonant‐absorption experiments. The collision cross sections and correlation parameters used in this description are defined in terms of the changes in rotational motion produced in collisions. These results permit quantitative study of intermolecular torques and molecular‐collision dynamics by the methods of nonresonant microwave absorption and nuclear resonance.

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