CE30 - Physique de la matière condensée et de la matière diluée

Theoretical & Experimental spectroscopic Methods for EXtreme conditions: in depth investigation of spectral signatures of small hydrocarbons and radicals – TEMMEX

Submission summary

The TEMMEX PRCI proposes a coherent and balanced network of three French and two Russian laboratories with internationally recognized expertise in complimentary domains of molecular spectroscopy. It aims at in depth investigations of the electronic structures, radiative properties and high-resolution spectral signatures of small hydrocarbons (HC) and their radicals, which is one of the most important molecular family {CnHm} for atmospheric and astrophysics, environmental science and technology. Spectral analyses represent excellent non-invasive tools for remote sensing and efficient control of gaseous media in various environments. However, the most of reliable high-resolution spectral data have been collected for stable semi-rigid species at stationary conditions. The TEMMEX project focuses on the understanding of HC spectral properties in extreme dynamical and temperature conditions, involving implementation and interpretation of new experiments beyond standard local thermodynamic equilibrium (LTE). This includes free-radicals which possess complex open shell electronic structures and non-rigid species allowing for large amplitude nuclear motion that represents a challenge for accurate theoretical spectra predictions. This brings us to the target the HC family up to eight atoms: {CH2, C2H, CH3, C2H2, CH4, C2H4, C3H4, C2H6}. To be reliable, theory will be experimentally validated for various cases of electronic structures, nuclear configurations, rovibrational motions and symmetries. Advanced experimental methods will be implemented to produce high-resolution absorption spectra from the far-infrared up to the visible. A wide range of temperatures will be explored from 100 to 296 K under LTE conditions in static gas cells, and from 10 to 2000 K under low and high velocity conditions for which the internal degrees of freedom are decoupled. A large panel of experiments including Fourier transform spectroscopy, ultra-sensitivity Cavity Ring Down Spectroscopy, Cavity Enhanced Absorption Spectroscopy, or Cavity Enhanced Optical Frequency Comb Spectroscopy will provide spectroscopic information in a wide range of temperature conditions (e.g. 100 K at LTE; down to 10 K in jet; up to vibrational temperatures of several thousand kelvins in non LTE plasma) for validating theoretical line lists calculated by TEMMEX theoreticians. Drastic reduction of the spectral congestion at low temperature will be valuable to identify band origins, while hypersonic shock wave compression experiments will give key insights on highly excited quantum states. Particular care will be taken to provide line intensity information as radiative Einstein coefficients, which are largely lacking in the literature for the considered species though they are crucial for many applications.. Free radicals will be formed at high vibrational temperature and low rotational temperature by radiofrequency plasma discharge in a supersonic jet expansion and probed with a new frequency comb spectrometer coupled to an optical cavity for a fast spectra recording on a large spectral range. The interpretation of spectral signatures will be carried out via first principle ab initio and variational methods. New line lists produced by theoretical methods and validated via analyses of experiments will be applied for assigning hydrocarbon traces in the atmospheres of Titan and outer planets. The TEMMEX consortium will allow tackling the very demanding above challenges in the best conditions. In particular, the past collaboration between two of the French partners (GSMA and LIPhy) and IAO-Tomsk in the frame of the Laboratoire International Associé SAMIA (2014-2018) has illustrated the synergy of the involved teams and insures a fluent communication. The involvement of the IPR-Rennes and TSU-Tomsk with unique experimental and theoretical expertise opens new horizons addressing new aspects in molecular spectroscopy in particular the spectroscopy of gases far from LTE.

Project coordinator

Monsieur MICHAEL REY (Groupe de Spectrométrie Moléculaire et Atmosphérique)

The author of this summary is the project coordinator, who is responsible for the content of this summary. The ANR declines any responsibility as for its contents.


IAO Institute of Atmoaspheric Optics, Russian Academy of Sciences / Departement of Spectroscopy
GSMA Groupe de Spectrométrie Moléculaire et Atmosphérique
LIPHY Laboratoire Interdisciplinaire de Physique
TSU Tomsk State Research University / Laboratory of Molecular Quantum Mechanics and Radiative Processes (QUAMER)

Help of the ANR 598,133 euros
Beginning and duration of the scientific project: December 2021 - 36 Months

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