[en] Within the framework of basic research on the flow and transport processes in separation nozzles for enrichment of the U-235 uranium isotope absorption measurements were performed with a tunable CO²-laser in a slit-shaped opposed-jet nozzle system operated with a model gas mixture consisting of perfluoromethyl cyclohexane (C⁷F¹⁴) and helium. The results of the density measurements suggest to conclude that, in conformity with earlier measurements made with free molecular probes, disturbances occur in the equilibrium of the translational motions of the mixture components. Accordingly, the heavy component is accelerated at a slower rate in the expansion zone of nozzle flow and in the compression zone it is decelerated less quickly than the light auxiliary gas. From the measurements of the C⁷F¹⁴ band temperature in the flow it can be concluded that there are pronounced disturbances in the distributions of energy between the translational motion and the internal degrees of freedom of this component. These non-equilibrium effects of the energy of the internal degrees of freedom detected here get manifest above all by the reduction of the 10.25 μm band temperature in the zone of C⁷F¹⁴ partial density rise, i. e. in the zone of stagnation of the opposed-jets and they appear also in the flow of pure C⁷F¹⁴, independent of the presence of a light auxiliary gas. (orig./HP)