Chemical Kinetics

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Saturne et ses lunes, Titan, Encelade, Dioné, Rhéa et Hélène. Les modèles d’atmosphère planétaire requièrent les constantes de vitesse d’une grande variété de réactions en conditions extrêmes. Image credit: NASA/JPL/Space Science Institute

Saturn and the moons Titan, Enceladus, Dione, Rhea and Helene. Models of planetary atmospheres need rate constants for a wide variety of reactions under extreme conditions. Image credit: NASA/JPL/Space Science Institute

The efficiency of a chemical reaction is described by its rate constant, k. Models of the atmospheres of planets such as Saturn or its moon, Titan, as well as even colder environments such as dense interstellar clouds, require a knowledge of thousands of rate constants. The majority of these are estimated as no measurements exist, especially at low temperature, and calculations are not sufficiently precise. We specialise in experimental measurements of these important physical quantities. The results of our measurements are integrated into databases such as KIDA which serve the interstellar and planetary atmospheric modelling communities.

Fast Reactions at Low Temperatures?

Reaction potential energy paths with (a) and without (b) a barrier to reaction.

Reaction potential energy paths with (a) and without (b) a barrier to reaction.

Most reactions have to proceed over an energetic barrier on the minimum energy path from reactants to products, and this means that they get slower at low temperatures. But some reactions, notably those between ions and molecules, do not have to pass over a barrier to react. Such reactions can remain fast even down to the very low temperatures of interstellar space. Here in Rennes we have discovered whole classes of ordinary reactions between neutral species also possess no overall barrier to reaction and become faster as the temperature drops. The formation of dimers, the first step in the important process of condensation and particle formation, is also a barrierless process. And the transfer of energy between colliding partners remains very rapid at low temperatures, and is vital for the correct interpretation of astronomical observations.

You can read more about our work in these four areas of chemical kinetics by clicking on the links below:

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