Collision-induced absorption, CIA

The advent of the laser has stimulated new research in collisional physics. The term laser-assisted collision was coined to describe the various research activities that have evolved. These studies are concerned with electronic transitions in supermolecules and will be briefly considered here. Similarities between laser-assisted collisions (LAC) and collision-induced absorption (CIA) exist, both in the types of phenomena considered and in the calculations of the spectra [208]. 

Table 7.1. Comparison of laser-assisted collisions (LAC) and collision-induced absorption (CIA) [208],...

The interaction-induced dipole moment of two dihydrogen molecules was reported by Li et The property was calculated at the CCSD(T) level of theory with a aug-cc-pV5Z basis set. This is the more advanced investigation of the interaction dipole moment of H2-H2 to date. Subsequently, the obtained data were used for calculation the collision-induced absorption (CIA) spectra of dihydrogen pairs. 

A proper analysis of the troposphere requires accurate collision-induced absorption (CIA) coefficients for the various relevant gases. Once quantum-mechanical calculations for N2-CH4 CIA became available (Borysow Tang, 1993), accurate atmospheric models became feasible. In order to suppress synthetic spectra sufficiently between 200 and 300 cm to fit the data, it was necessary to fill the upper... 

According to theory, most collision-induced absorption spectra should not only consist of contributions of the free-state to free-state transitions typical of collisional pairs, but also of contributions arising from bound-to-free and bound-to-bound transitions involving van der Waals molecules. In the rotovibrational spectra such dimer bands have been known for some time, but in CIA studies of the rototranslational band, where path lengths have generally been limited to a few meters, dimer features have been seen only recently [268], The dimer spectra are an integral part of the interaction-induced absorption. 

For the H2-H2 rototranslational band the collision-induced absorption spectrum was seen to be composed of essentially eight components labeled AiA2AL = 2023, 0223, 2021, 0221, 2233, 2211, 4045, and 0445 [282], Of these, the three pairs 2023 and 0223 2021 and 0221 4045 and 0445 are identical pairs. For the fundamental band, we have another important component, namely A1A2AL = 0001 (dotted in the figures) arising from overlap induction. That component is familiar from the CIA spectra of gas mixtures. It occurs here because a vibrating H2 molecules differs from a non-vibrating one. Furthermore, the pairs like 2023,0223, etc., are not identical any more, for the same reason. 

When in 1989 Dr. Alex Dalgarno asked me if I wanted to write a book on collision-induced absorption of gases, I did not hesitate for long. The present monograph is the first attempt to review measurement and theory of CIA in gases at densities which, on the one hand, are high enough so that collision-induced absorption is observable and, on the other, low... 

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