On calculation of the molecular line shape in the wings

Abstract

The general formulation of the molecular spectral line shapes is treated in a consistent way in the two limiting regions of the core and wings of a line. We have extended the scope of the quasistatic theory of Margenau by explicitly introducing, for an anisotropic interaction, the influence of the non-resonant character of the exchange of quanta between the active molecule and its surroundings, which is of particular importance for molecular collisions. The present development is restricted to the two first orders with respect to the perturbing potential and includes a convenient cutoff procedure. It is shown that, for the exactly resonant limit, we obtain the exact frequency dependence with an error less than 10% with respect to the result of the infinite-order theory. We expect that the procedure will also give acceptable results for non-resonant interactions, where the Margenau treatment does not apply.