EFFECTS OF THE SPATIAL-DISPERSION AND INSTABILITIES IN THE WAVE ELECTRODYNAMICS OF WEAKLY IONIZED-GASES

The complex spectra of transverse and longitudinal modes in the conduc ting gas of two-level (or quasi-classical) molecules are found, taking into account the spatial dispersion due to the thermal motion of mole cules. Conditions for the existence of weakly damping longitudinal wav es and transverse polarization waves, as well as of electromagnetic wa ves with the dispersion law much different from the ''vacuum'' dispers ion law (which is well known in spectroscopy as the Voyght one and inc ludes Doppler broadening according to the perturbation theory) are spe cified. The collisionless damping modes (on the wings of the Doppler l ine) with the dispersion law determined by the zeroes of the complex e rror function are studied. The analogy with the collisionless Landau d amping of the Langmuir waves in electron plasma is established. It is shown that, in the neutral gas of excited molecules, the longitudinal and transverse polarization waves possess negative energy and may lead to the dissipative and beam-type instabilities.