MOLECULAR RELAXATION IN SUPERSONIC FREE JETS OF N-2 AND CH4 FROM STIMULATED RAMAN-SPECTROSCOPY AND TIME-OF-FLIGHT MEASUREMENTS

The relaxation of the energy stored in the translational and rotationa l degrees of freedom of N-2 and CH4 in the course of free jet expansio ns has been experimentally studied. Rotational temperatures along;he e xpansion axis were obtained by means of stimulated Raman spectroscopy, and terminal flow velocities and translational temperatures were dete rmined item supersonic beam time-of-flight measurements. From these me asurements low-temperature cross sections for rotational relaxation ha ve been estimated. The results are compared with data from other exper iments, and the validity of simple relaxation models is discussed.