POPULATIONS OF ROTATIONAL LEVELS OF NITROGEN MOLECULES IN FREE JETS -COMPARISON OF CARS AND ELECTRON-BEAM FLUORESCENT TECHNIQUE

The paper presents experimental data on the distribution of the rotati onal level populations of nitrogen molecule ground state, N-2(X(1)Sigm a(g)(+),nu = 0). The results have been obtained on the axis of the fre e jet in stationary and impulse regimes. Two diagnostic techniques (th e CARS and Electron-Beam Fluorescent) were used. The perfect coinciden ce of the results obtained by these two methods in the identical condi tions is shown. Good agreement has been also obtained with the results of measurements by LIF and Raman spectroscopy methods. All methods re veal a breakdown of Boltzmann distribution of rotational level populat ion time during gas jet expansion into vacuum. It is found that additi onal disturbance of Boltzmann distribution is connected with the relea se of the energy of condensation into gas jet under high stagnation pr essures. (C) 1998. Published by Elsevier Science B.V. All rights reser ved.