The paper presents the results of experiments on irradiation of air molecules with biharmonic radiation of Nd-YAG-laser second harmonic (two longitudinal modes). It was recorded about 750 lines in the emission spectrum of thus excited molecules within the region from 0,198 to 0,394 μm. These lines are due to transitions between excited electron stats of N2 molecules as well as of the molecular ions N2+ and O2+, and of the ionized atoms N+ and O+. It is shown in this paper that the effect, can only be observed in the media containing molecules with the rotational energy levels irradiated with a biharmonic field, the difference of energies between he waves of which is in resonance with the energy of a rotational state of a molecule. Interpretation of the experimental results is based on the qualitative analysis of differential equations of motion. Finally, the analysis made allowed us to state that there exist a stationary point of the "centre" type and an asymptotic cycle with the "screw-on" on it trajectories (regardless of their initial conditions). As a consequence, a rigid rotator placed in a biharmonic resonant (at the difference frequency) field can be considered as a synergetic system.
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