LINE MIXING IN A CO2 Q BRANCH BROADENED BY Ar AND He
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Date
1990
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Ohio State University
Abstract
Previous studies of Q-branch line mixing in infrared spectra involved self- and $N_{2}$-broadened spectra of $CO_{2}$ and $N_{2}O$. A phenomenological theory of collisional rotational relaxation has been reasonably successful in describing the lineshapes in these systems. Ab-initio calculations have not been tested due to the complexity of the molecule-molecule collision process. Ab-initio calculations are possible for atom-molecule collisions, especially for $CO_{2}-He,Ar$ collisions, for which good potentials exist. We have recorded Ar- and He-broadened spectra in both $CO_{2}$ and $N_{2}O$ Q branches in order to test the ability of ab-initio calculations to predict line mixing and to determine the general suitability of the presently used phenomenological theory for collisional relaxation. Spectra calculated using ab-initio theory and the phenomenological approach agree very closely for $CO_{2}$ broadened by He. However, both calculations predict significantly less line mixing than observed.
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Author Institution: Department of Physics, University of Maryland Baltimore County; NASA Goddard Space Flight Center, Institute for Space Studies