Partial Inversion in Small Molecules: New Potentialities for the Spectroscopic Diagnostics of Gases

摘要

The formation of vibrational-rotational absorption spectra of small molecules in vibrationally nonequilibrium conditions, with the possibility of manifestation of partial population inversion of levels and negative absorption, is studied. Specific features of the partial inversion in linear and top molecules are analyzed. It is shown that water vapor is the best object among atmospheric gases for the realization of this effect. Formulas for the integrated line intensities and the absorption coefficient of two- and three-level nonequilibrium vibrational systems with a rotational structure are obtained. It is shown that the partial-inversion effect can be used to study weak vibrational-rotational transitions. Concrete calculations for the (000)-(010)(020) bands of water molecules at different temperatures are made. The frequencies are determined for which negative absorption is the strongest.