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Chapitre D'ouvrage Année : 2022

Infrared Absorption Spectroscopy in Laval Nozzle Supersonic Flows

R. Georges
E. Dudás
L. Rutkowski

Résumé

The extraordinary cooling caused by the supersonic expansion of a polyatomic gas on its infrared footprint has been extensively employed for applications ranging from nucleation studies to post-shock spectroscopy. In this chapter, we recall the benefits of decreasing the molecular sample temperature, involving the spectral simplification and the subsequent magnification of the absorption transitions starting from the lowest rotational energy levels, the drastic line width narrowing, the supersaturation, the formation, and stabilization of weakly bounded molecular complexes. These effects are illustrated by infrared spectra of, e.g. water, carbon dioxide, methane, and more complex molecules such as trans-butadiene or naphthalene. The scope of this chapter includes different types of flows obtained using the Laval nozzle: perfectly expanded or slightly overexpanded flows produced by contoured Laval nozzles, and underexpanded flows produced by simpler conical divergent nozzles. The various infrared spectroscopic techniques coupled with Laval nozzle flows are also reviewed. Conventional techniques like tunable diode laser absorption spectroscopy (TDLAS) and Fourier transform infrared spectroscopy (FTIR) have been intensively applied to the study of homogeneous nucleation. Other recent and more sensitive techniques such as cavity ring-down spectroscopy (CRDS), cavity enhanced absorption spectroscopy (CEAS), and optical frequency comb spectroscopy (OFCS) are now used for the measurement of reaction kinetics in the infrared, or for the non-ETL spectroscopy of molecules such as methane, which is of great astrophysical interest. © 2022 by World Scientific Publishing Europe Ltd.
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Dates et versions

hal-03932086 , version 1 (10-01-2023)

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Citer

R. Georges, E. Dudás, N. Suas-David, L. Rutkowski. Infrared Absorption Spectroscopy in Laval Nozzle Supersonic Flows. Uniform Supersonic Flows in Chemical Physics: Chemistry Close to Absolute Zero Studied Using the CRESU Method, World Scientific Publishing Co., pp.479-538, 2022, 9781800610996; 9781800610989. ⟨10.1142/9781800610996_0009⟩. ⟨hal-03932086⟩
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