Otoniel Denis Alpizar

Abstract

Experiments to study molecular processes under extreme conditions, such as the very low densities of interstellar molecular clouds and the enormous temperatures around spacecraft during atmospheric re-entry, are often complex and expensive. Therefore, theoretical and  computational studies have become essential for understanding the chemical processes in such environments. The study of molecular interactions is crucial for determining reactive rate coefficients, which are used as input in aerothermodynamic models and astrochemical networks. Inelastic rate coefficients are essential for non-LTE models used to analyze  interstellar observations. Reactive and inelastic collisions can be studied using a general methodology based on three steps. First, a set of ab initio energies is calculated for many  geometric configurations of the system under study. Second, the calculated energy lattice is  fitted to an analytical potential energy surface (PES). Developing an analytical function for reactive systems is more complicated than for van der Waals complexes because it involves  multiple channels and requires a large ab initio energy grid. Third, the calculated PES is  incorporated into a dynamics code that computes a large set of state-to-state reaction probabilities (for reactive systems) or inelastic cross-sections (for non-reactive systems). Finally, the rates are determined from these data. This talk examines this methodology with  several examples of interest in astrochemistry and hypersonic regimes from recent studies.