Theory monatomic gas mixtures

The theory of collision-induced absorption developed by van Kranendonk and coworkers [405] and other authors [288, 289, 81, 126, 125] has emphasized spectral moments (sum formulae) of low order. These are given in closed form by relatively simple expressions which are readily evaluated. Moments can also be obtained from spectroscopic measurements by integrations over the profile so that theory and measurement may be compared. A high degree of understanding of the observations could thus be achieved at a fundamental level. Moments characterize spectral profiles in important ways. The zeroth and first moments, for example, represent in essence total intensity and mean width, the most striking parameters of a spectral profile. 

Attempts have been made to construct translational band shapes from more or less sophisticated dynamical models. When such computations 

In this Chapter, we consider the theory of collision-induced absorption by rare gas mixtures. We look at various theoretical efforts and compare theoretical predictions and computations with measured spectra and other experimental facts. The theory of induced absorption is based on quantum mechanics, but in certain cases, the use of classical physics may be justified, or indeed be the only viable choice. The emphasis will be on the computation of induced absorption by non-reactive, small atomic systems in the infrared. Diatomic and triatomic systems show most of the features of collisional absorption without requiring complex theory for their treatment. The theory of induced absorption of small clusters involving molecules will be considered in Chapter 6. 

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