Water vapor line wing absorption and violation of the long-wave approximation for molecular centers of mass

Аннотация

Further development of the asymptotic line wing theory is presented where the long-wave approximation for the molecular centers of mass is violated. This provides long molecular trajectories going far beyond an elementary volume in the case of nonresonance light absorption. The occurrence of long trajectories is evidence for a certain degree of ordering of molecular chaos. The latter can be described by means of a modified semiclassical representation method to establish correlation between the displacement and velocity operators. An expression for the absorption coefficient is derived that allows an ambiguity concerning the estimation of the parameters of the potentials to be avoided, and the temperature dependence of the absorption coefficient in line wings to be described. In our earlier work, calculations of the absorption coefficient were performed with violation of the long-wave approximation for molecular centers of mass for H₂O molecule in the 8–12 μm region using a diffusion model. This model is also employed in the present work for H₂O absorption in the 3–5 μm window regions and for CO₂ absorption in the 4.3-μm band wing to describe the temperature dependence of the absorption coefficient. Long molecular trajectories essential for the 8–12 and 3–5 μm H₂O regions are shown to hardly play a role in the 4.3-μm CO₂ band wing.