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M.-C. Gazeau, H. Cottin, V. Vuitton, F. Raulin (LISA, Univ. Paris 12)
Coupling the data obtained from laboratory experiments, theoretical modelling and observation is the way to draw a quite precise picture of the organic chemistry involved in a cometary environment or a planetary atmosphere. We specifically discuss the contribution of laboratory experiments to models in the cases of both cometary and Titan investigations. In the case of cometary studies, we point out the lack of fundamental data such as kinetic rate constants and quantum yields necessary to build theoretical models. We present a photochemical program named ``S.E.M.A.Ph.Or.E. Cometaire" dedicated to provide such parameters. The aim of this experimental work is to support the theoretical modelling of interactions between the cometary nucleus and the coma's molecular composition. It provides, in particular, useful information on the origin of the H2CO and CN extended sources. In the case of Titan's studies, we discuss the limitations of global simulation experiments with respect to extracting useful data for modelling. We present a simple well-constrained laboratory experiment dedicated to the study of specific photochemical reactions occurring in Titan's atmosphere. The comparison of experimental data with those obtained from theoretical models leads to a critical examination of the accuracy of the model's chemical schemes. We illustrate this approach with the study of the catalytic dissociation of methane by acetylene supposed to occur in Titan's stratosphere.