title: Strong thermal nonequilibrium in hypersonic CO and CH4 probed by CRDS.
abstract: A new experimental setup coupling a High Enthalpy Source (HES) reaching 2000 K to a cw-cavity ring-down spectrometer has been developed to investigate rotationally cold hot bands of polyatomic molecules in the [1.5, 1.7] μm region. The rotational and vibrational molecular degrees of freedom are strongly decoupled in the hypersonic expansion produced by the HES and probed by cavity ring-down spectroscopy. Carbon monoxide has been used as a first test molecule to validate the experimental approach. Its expansion in argon led to rotational and vibrational temperatures of 6.7 ± 0.8 K and 2006 ± 476 K, respectively. The tetradecad polyad of methane (1.67 μm) was investigated under similar conditions leading to rotational and vibrational temperatures of 13 ± 5 K and 750 ± 100 K, respectively. The rotationally cold structure of the spectra reveals many hot bands involving highly excited vibrational states of methane.
authors.affiliation: Laboratoire Interdisciplinaire Carnot de Bourgogne, UMR 6303 CNRS-Université de Bourgogne Franche-Comté, 9 Avenue Alain Savary, BP 47870, F-21078 Dijon Cedex, France.
authors.forename: M
authors.initials: M
authors.lastname: Louviot
authors.affiliation: Institut de Physique de Rennes, UMR 6251, Campus de Beaulieu, Bât 11C, Université de Rennes 1/CNRS, F-35042 Rennes Cedex, France.
authors.forename: N
authors.initials: N
authors.lastname: Suas-David
authors.affiliation: Laboratoire Interdisciplinaire Carnot de Bourgogne, UMR 6303 CNRS-Université de Bourgogne Franche-Comté, 9 Avenue Alain Savary, BP 47870, F-21078 Dijon Cedex, France.
authors.forename: V
authors.initials: V
authors.lastname: Boudon
authors.affiliation: Institut de Physique de Rennes, UMR 6251, Campus de Beaulieu, Bât 11C, Université de Rennes 1/CNRS, F-35042 Rennes Cedex, France.
authors.forename: R
authors.initials: R
authors.lastname: Georges
authors.affiliation: Groupe de Spectrométrie Moléculaire et Atmosphérique, UMR CNRS 7331, Université de Reims, UFR Sciences Exactes et Naturelles, BP 1039, F-51687 Reims Cedex 2, France.
authors.forename: M
authors.initials: M
authors.lastname: Rey
authors.affiliation: Université Grenoble Alpes, LIPhy, F-38000 Grenoble, France and CNRS, LIPhy, F-38000 Grenoble, France.
authors.forename: S
authors.initials: S
authors.lastname: Kassi