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Title:HIGH-TEMPERATURE HYPERSONIC LAVAL NOZZLE FOR NON-LTE CAVITY RINGDOWN SPECTROSCOPY
Author(s):DUDÁS, Eszter
Contributor(s):Georges, Robert ; Charles, Christine ; Kassi, Samir ; Benidar, Abdessamad ; Kulkarni, Vinayak ; Brahmachary, Shuvayan ; Suas-David, Nicolas
Subject(s):Vibrational structure/frequencies
Abstract:The SMAUG apparatus (Spectroscopy of Molecules Accelerated in Uniform Gas flows) was developed to produce non-LTE spectra of various molecules of interest for hot astrophysical atmospheres, like the one surrounding hot Jupiters, reaching up to 2500K. High-temperature IR spectroscopic data is needed to retrieve temperature and concentration profiles from astronomical spectra. This work is done in the frame of the e-PYTHEAS project that focuses on high-temperature spectroscopy of small hydrocarbons. A small dimension Laval nozzle connected to a compact high enthalpy source equipped with cavity ringdown spectroscopy (CRDS) is used to produce vibrationally hot and rotationally cold high-resolution IR spectra of polyatomic molecules in the 1.67~$\mu$m region.$^{a}$ The nozzle was designed to operate with argon heated up to 2000~K and to produce a quasi-unidirectional flow to reduce the Doppler Effect responsible for line broadening. This novel approach was applied to carbon monoxide and methane. Vibrational (T$_{vib}$) and rotational (T$_{rot}$) temperatures were extracted from the recorded infrared spectrum leading to T$_{vib}$~=~1346~$\pm$~52~K and T$_{rot}$~=~12~$\pm$~1~K for CO. A rotational temperature of 30~$\pm$~3~K was measured for CH$_{4}$, while two vibrational temperatures were necessary to reproduce the observed intensities. The population distribution between vibrational polyads was correctly described with T$_{vib,I}$~=~894~$\pm$~47~K, while the population distribution within a given polyad (namely the dyad or the pentad) was modelled correctly by T$_{vib,II}$~=~54~$\pm$~4~K, testifying to a more rapid intra-polyad vibrational relaxation. \line(1,0){490}\\ $^{a}$E.Dud$\acute{a}$s \emph{et al.} J. Chem. Phys. submitted (2020)
Issue Date:25-Jun-20
Publisher:International Symposium on Molecular Spectroscopy
Citation Info:APS
Genre:CONFERENCE PAPER/PRESENTATION
Type:Text
Language:English
URI:http://hdl.handle.net/2142/107660
Date Available in IDEALS:2020-06-26


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