The chemistry of the interstellar medium (ISM) has become an important area of research in recent years. Thanks to instrumental developments, many new molecules are discovered every year, increasing our knowledge of the complexity of the ISM. The physical conditions in such regions – characterized by very low temperature and density - are very different to what we experience on Earth. It has been necessary for experimental chemists to develop novel techniques to measure the reactivity of chemical species in ISM-like conditions. It is only recently however that astrochemists have begun to understand the importance of neutral-neutral reactions in the ISM, whose behaviour at low temperature remained largely unknown until recently. Nevertheless, astrochemical reaction networks include studied and unstudied neutral-neutral reactions alike, with the rate coefficients for the unstudied reactions being simply estimated in the model. Thus, the chemistry in these models, which is largely driven by not quantified reactions, is subsequently used by astronomers to simulate the chemistry of the ISM in star and planet forming regions. To draw any substantial conclusions from the comparison between the observations and the models, it is crucial to know the model limitations due to uncertainties in the reaction rate coefficients. In this proposal, we wish to bring together different but complementary fields: experimental chemists studying low temperature reactions and astronomers modelling interstellar chemistry. The astronomer of our project is working actively to improve chemical networks for the ISM. She has developed a number of numerical tools to estimate the uncertainties in theoretical species abundances due to rate coefficient imprecision to give a quantitative meaning to the model predictions. She has also developed methods to prioritize reactions that need to be studied by experimental chemists. The chemists of our project have been working for several years on the kinetics of neutral-neutral reactions at low temperature. This team is currently working on the creation of a unique and comprehensive chemical database for astrochemistry (the ISM and planetary atmospheres): KIDA (KInetic Database for Astrochemistry). Such a tool is required to optimize the efficiency of the collaboration between chemists and astrochemists. KIDA is constructed to be useful for astrophysicists and planetary scientists, and to make the chemists work visible to the entire community. This ANR proposal concerns the development of KIDA and the improvement of the data for nitrogen chemistry contained within. For the construction of KIDA, we ask for an assistant engineer who will be responsible for the development of the web interface and for feeding the database. The second part of this proposal concerns the construction of a new experiment to measure the reactivity of atoms with radicals. Although these processes present a challenge for experimentalists, they would be a significant advance for astrochemistry since such reactions are highly important in the ISM. With this new experiment, we would also be able to measure absolute branching ratios for the products of these reactions. Although N-bearing chemistry is typically used to probe the chemical processes that occur during the cold pre-stellar phases, reactions between N atoms and radicals have never been studied at low temperature. We will focus on the most important reactions of atomic nitrogen, identified by the numerical tools previously described. In order to utilize all the information obtained by the experimentalists, we will improve the numerical tools developed to simulate the interstellar chemistry and in particular the treatment of branching ratios uncertainties. Using the new experimental results and new astrochemical models, we will make a detailed analysis of the impact of the measured rate coefficients on the chemistry in star forming regions. Considering the sensitivity of present models to the selected reactions, we expect significant changes in the predictions for nitrogen chemistry in the ISM. The final goal of the project is to improve the predictions of chemical models for the different stages of star and planet formation and be ready for the most powerful observing instruments in this field: the Herschel Space Observatory (HSO) and the Atacama Large Millimeter Array (ALMA).