A classical dynamics study of Senftleben-Beenakker effects in nitrogen gas

An extensive body of experimental data is presently available on Senftleben-Beenakker and related effects for a variety of polyatomic gases. This data presents the theoretician with an opportunity to test approximations in kinetic theory, collision dynamics, and anisotropic intermolecular potential functions. Although both formal theoretical developments and quantum mechanical computations have been areas of considerable activity, it has only been feasible to apply the usual numerical quantum mechanical techniques to hydrogen isotopic molecules. In this paper, we provide theoretical results for affective cross sections for one of the heavier collisions systems that has been thoroughly studied experimentally. We have developed an approach in which classical ansatz equations for the various effective cross sections are derived and evaluated via classical trajectories. As in a previous study of depolarized Rayleigh line broadening, where the classical ansatz expression was shown to be identical to a semiclassically derived expression, the system N2−N2 has been chosen for the present investigation. The relative importance of the “second molecule” contributions to the various effective cross sections as well as the role of quadrupole-quadrupole forces have been explored. In general we find close agreement between the calculated results and experiment for effective cross sections involving only molecular velocity terms and poorer agreement for those which also include angular momentum terms. The results show that the present approach provides considerable insight into the microscopic collisional processes and intermolecular forces which give rise to the observable cross sections, as well as providing an opportunity to compare computational results with experiment.