Rotation and Rotation-Vibration Pressure-Broadened Spectral Lineshapes

Abstract

The last comprehensive review of rotational spectral lineshapes was by Birn­ baum (1) in 1967. Since then a considerable number of experiments have been performed, providing additional insight into the basic theory of lineshapes. The present review emphasizes developments since the earlier review, although material previous to that is cited when necessary. It is instructive to examine why spectral lineshapes, rotational or otherwise, have received such wide experimental and theoretical interest. The answer en­ compasses both practical and basic physical concerns. For example, the design and operation of gaseous molecular lasers require knowledge of the pressure­ induced widths and shifts of the spectral lines. Engineers interested in radiative transfer in the atmosphere (2,3) need to know the location of the spectral windows and their absorption characteristics. Such energy transmission charac­ teristics can be sensitive to the wings of the atmospheric spectral lines. Studies of pollutants in the atmosphere have also drawn on spectral lineshape data for developing measurement techniques. The necessity for such lineshape data has stimulated research in this area (4, 5). Radiative transfer research has not been restricted to our own atmosphere (6). For example, the widths of CH4 and NH3 lines broadened by CH4 (7-9) are relevant factors in the spectral transmission in the atmosphere of Jupiter. In the absence of direct measurements, the line­ strength of CO and its CO2 broadened width would be helpful for studying the presence of CO in the Martian atmosphere, as pointed out by Tubbs (10). In addition to the above experimental and practical considerations, other research has focused on the analysis of spectral lineshapes in order to study the physical phenomena responsible for the shapes themselves. This is the emphasis