A kinetic approach to the shape of pressure broadened molecular bands

A unified treatment of the shape of pressure‐broadened molecular absorption bands from near resonance to the far wings is obtained by a kinetic approach using memory functions. Empirical models for these functions are employed that interpolate between their known short and long time behavior. This treatment includes the following band shaping mechanisms: line interference, finite duration of collision, and molecular torques which incorporate initial orientational correlations. Line interference can produce a very sharp decrease in absorption in the periphery of the band, although this effect may be moderated by the finite duration of collision. Absorption in the far wings, which exhibits a much less rapid decrease with increasing frequency, is attributed to the effect of molecular torques acting during collisions. By using model memory functions, a simple analytical expression is obtained for the far wing absorption. The parameters in these models are related to known molecular quantities.