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In the present work, static and dynamic quantities of carbon dioxide (CO2) are studied by means of Raman spectroscopy in gas flows.
CO2 is a molecule of great importance in several current challenges, like characterization of exoplanets atmospheres, development of accurate climate models or synthesis of fuels through plasmas. Most of these problems involve non-local thermodynamic equilibrium (nLTE) conditions. Therefore, deep understanding of relaxation (and excitation) processes is needed in order to work on the aforementioned questions.
Supersonic jets in the laboratory provide an ideal medium to investigate these mechanisms. Combined with Raman spectroscopy, information on the evolution of the populations of the molecules can be retrieved and a detailed study of its relaxation along the jet can be made [1,2]. Nevertheless, this experimental method raises another problem: Raman spectroscopy strong dependency on the polarizability transition moments of the molecule under study. Although this quantity is well-known for CO2 rotational Raman transitions, reliable data for vibrational transitions is missing [3].
We present a set of results for both problems. On the one hand, by generating high-temperature flows of CO2 in thermodynamic equilibrium, a set of measurements of the polarizability transition moments have been obtained for more than 30 vibrational Raman transitions. On the other hand, we probed several supersonic jets of CO2 from hot nozzles by Raman spectroscopy, obtaining a set of state-to-state rate coefficients for rotational relaxation for a wide range of temperatures.
[1] A. Ramos, G. Tejeda, J. M. Fernández, S. Montero, J. Phys. Chem. A 114, pp. 7761 (2010).
[2] S. Montero, G. Tejeda, and J. M. Fernández, Astrophys. J. Suppl. Series 247, 14 (2020).
[3] R. Lemus, M. Sánchez-Castellanos, F. Pérez-Bernal, et al. J. Chem. Phys. 141, 054306 (2014).
