How does energy move between translational and rotational motion in gas molecules?

In the context of gas molecules, energy transfer between translational motion (displacement in space) and rotational motion (spinning and tumbling) occurs through molecular collisions.1

These processes are categorized as physical relaxation phenomena. Unlike the transfer of energy between translational and vibrational modes, which may require thousands of collisions, the exchange of energy between translational and rotational degrees of freedom is highly efficient and typically requires only a few molecular collisions to reach equilibrium.1

Because these energy transfers are not instantaneous and depend on the frequency of collisions, they are time-dependent. Scientists investigate these dynamics by measuring sound absorption in gases, which allows them to observe how energy redistributes among the independent forms of molecular motion. This study of relaxation provides critical insights into the nature of molecular bonding and structure.1