Spectral line shape. I. Kinetic equation for arbitrary frequency detunings

Abstract

A theoretical formulation of the problem of the spectral line shape is presented using the superoperator technique. Conventional approximations, such as the long wave approximation, the binary approximation and the classical motion of molecular centers of mass, are employed. The kinetic equation for the line profile from resonance to the far wings is derived. Its main feature is that the terms prevailing at small or large frequency detunings are separated in the equation itself.

Water-vapor foreign-continuum absorption in the 8–12 and 3–5μm atmospheric windows

“…In doing so, the problem of interaction between two molecules whose centers of mass are moving along classical trajectories remains a quantum problem with the quantum intermolecular interaction potential. A kinetic equation was derived in [20] for quantities defining the absorption coefficient in the asymptotic cases of small (line center) and large (line wing) frequency detunings. For large frequency detunings, the time integral was evaluated asymptotically [17,21].…”

“…According to the ALWT advanced in [17,20,21], the water vapor absorption in windows is determined by the effect of strong line far wings of neighboring monomer bands with a special line wing shape. A basic feature of the ALWT used to solve the general quantum problem of interaction of absorbing and broadening molecules is the application of the semiclassical representation method intended for the problems where part of variables can be considered as being classical, whereas the other variables remain quantum [22].…”

CO2 absorption in band wings in near IR

“…The CO 2 absorption in the 7000 and 8000 cm -1 spectral regions was considered from the viewpoint of the asymptotic line wing shape theory [14,25,26] under the assumption that the absorption is mainly determined by far wings of strong lines of adjacent bands of a monomer.…”

Continuum absorption by water vapor in the 8–12 and 3–5 μm atmospheric transparency windows

“…The asymptotic theory [4,15,16] considers the total quantum problem of the absorption of light by inter acting molecules as the initial one. The semiclassical approximation method is used in the solution of the problem of the interaction of two molecules.…”

“…Among possible theoretical explanations of the nature of the continuum absorption, in addition to the hypothesis on the monomer line wings (see [4,[15][16][17] and references in them), the hypothesis concerning the water vapor dimer absorption should be noted, which is experiencing some kind of renaissance at present due to the appearance of quantitative informa tion on dimer spectra [8][9][10][11][12][13]. However, let us note that this information relates mostly to the spectral intervals within water vapor absorption bands.…”