Chemische reactiviteit en excitatie bij lage temperatuur met kwantum statistische methoden

Complex molecular species are present in various astronomical environments, from the interstellar medium to protoplanetary disks and comets, and in-depth models have been developed to understand chemistry in these environments. A major bottleneck arises from the lack of data for reactive and inelastic collisions involving the various molecules present in space. In order to improve our understanding of astronomical environments as well as to guarantee the quantitative interpretation of observations made by new telescopes, the main objective of this project is to provide theoretical advances leading to a better understanding of gas-phase processes at low temperatures. We will consider in particular quantum statistical methods based on accurate ab initio potential energy surfaces in order to calculate quantum state resolved rate coefficients for reactions and collisions of molecular ions with the main constituents of the interstellar medium, He, H, and H2. A thermal reaction rate coefficient is often sufficient to describe chemical reactions. For ionic species, however, quantum-state resolved rate coefficients are required for a detailed modelling of the chemistry, while in the case of inelastic collisions, state-to-state rate coefficients are needed for molecules of increasing complexity. The statistical methods explored in this project allow the simultaneous treatment of the excitation and reactivity and are expected to be efficient for reactions involving ions. Complementary approaches will be implemented in order to improve the performances of these statistical methods, and the results will be benchmarked against accurate but computationally costly fully quantum-mechanical calculations for simple cases.