Populations of rotational levels of nitrogen molecules in free jets. Comparison of CARS and electron beam fluorescent technique Original Research Article

The paper presents experimental data on the distribution of the rotational level populations of nitrogen molecule ground state, N2(X1Σ+g,v=0). The results have been obtained on the axis of the free jet in stationary and impulse regimes. Two diagnostic techniques (the CARS and Electron-Beam Fluorescent) were used. The perfect coincidence of the results obtained by these two methods in the identical conditions is shown. Good agreement has been also obtained with the results of measurements by LIF and Raman spectroscopy methods. All methods reveal a breakdown of Boltzmann distribution of rotational level population time during gas jet expansion into vacuum. It is found that additional disturbance of Boltzmann distribution is connected with the release of the energy of condensation into gas jet under high stagnation pressures.