Low temperature chemical kinetics : The CRESU (Cinétique de Réaction en Ecoulement Supersonique Uniforme) / Laval nozzle method.

The objective is to obtain information on the reactivity of species present in astronomical environments (molecular clouds, planetary atmospheres...) or of reactions relevant to the Earth’s atmosphere. Reactions between neutral species which do not pass over an energy barrier are often seen to possess rate coefficients which increase with decreasing temperature or have unusual temperature dependences. Thus the extrapolation of these quantities measured at high temperatures using conventional methods, to low temperatures for use in astrochemical models, can be highly inaccurate. The CRESU technique is the only technique to date that allows the measurement of absolute rate data for gas phase reactions at very low temperatures. Nine Laval nozzles have been developed for the CRESU apparatus in Bordeaux which allow us to undertake experiments at 260K and 245K (with N2/SF6 as the carrier gas), 224K, 177K, 130K and 106K (with N2 as the carrier gas) and 135 K, 75 K and 50 K (with Ar as the carrier gas).

JPEG - 33 ko
Pumps__________________CRESU__________________Laval nozzles

Studied Reactions (50 - 220 K) :

- CH + allene, methylacetylene and propene
- C2(X1\Sigma+) + acetylene, methylacetylene, allene and propene
- C2(a3\Pi) + acetylene, methylacetylene, allene and propene
- OH + propene, 1-butene and allene
- N + NO, N + OH, N + CN
- Cl + ethane and propane

Thesis (Julien Daranlot) :

The thesis project involves the experimental study of the reactions of atomic nitrogen with molecular or radical co-reagents playing a role in the chemistry of the interstellar medium and in planetary atmospheres. The kinetic measurements will be performed at low temperatures (50 K to 220 K) in the Bordeaux CRESU apparatus, combining microwave discharge methods for atomic nitrogen production with pulsed laser techniques to produce the other reactive species and/or to probe them by laser induced fluorescence/cavity ringdown spectroscopy.

Collaborations and financial supports :

- ANR Jeunes Chercheuses et Jeunes Chercheurs, en sciences de l’univers et géo-environnement, 2009-2011, Valentine Wakelam du Laboratoire d’Astrophysique de Bordeaux
- Conseil régional d’Aquitaine, 2009-2011.
- Bourse européenne Marie-Curie (7th FrameWork Programme, FP7), 2009-2011, Kevin Hickson.
- Physique et Chimie du Milieu Interstellaire (PCMI) de l’INSU 2008.
- Environnements Planétaires et Origines de la Vie (EPOV) du CNRS 2011 (avec M. Dobrijevic du Laboratoire d’Astrophysique de Bordeaux).

Publications :

Elemental nitrogen partitioning in dense interstellar clouds.
Julien Daranlot, Ugo Hincelin, Astrid Bergeat, Michel Costes, Jean-Christophe Loison, Valentine Wakelam, Kevin M. Hickson,
PNAS (2012), 109, 10233-10238.

Revealing Atom-Radical Reactivity at Low Temperature Through the N + OH Reaction
Julien Daranlot, Mohamed Jorfi, Changjian Xie, Astrid Bergeat, Michel Costes, Philippe Caubet, Daiqian Xie, Hua Guo, Pascal Honvault, Kevin M. Hickson
SCIENCE (2011), 334, 1538 - 1541.

Gas-Phase Kinetics of hydroxyl Radical reactions with Alkenes : Experiment and Theory.
Julien Daranlot, Astrid Bergeat, Françoise Caralp, Philippe Caubet, Michel Costes, Wendell Forst, Jean-Christophe Loison, Kevin M. Hickson,
Chem. Phys. Chem. (2010), 11, 4002-4010.

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