Theories and simulations of molecular reactive collisions for primordial chemistry

In this PhD we present the analysis of the reactive dynamics of triatomic systems of interest for the primordial chemistry. Simulations have been mainly done using the quasi-classical trajectory formalism (QCT approach) for which a code has been developed. The iT code has the advantage of being able to determine the state-to-state rate constants with a low numerical cost and a large temperature domain. We have shown that the QCT results are very reliable in the high collision energy domain by realizing a limited number of time dependent quantum method calculations (MCTDH method). A huge number of rate constants (∼10⁵) has been determined for the systems H₃, H₂D, typical of direct processes. Our study also revealed the importance of dissociation for high temperature regime (T > 10³ K). The new kinetic data will permit to constrain the molecular abundances of H₂ and HD, hence giving reliable cooling functions for the dynamics study of collapse of the molecular clouds precursor of the first stars. Those data could be employed in interstellar medium in regions where high internal energy molecular states are relevantly populated (PDR or C-type shocks). We present the indirect reaction dynamics of the systems H₂D⁺ and HeH₂⁺. For those processes that can be characterized by a long lifetime intermediate complex, we have shown that an approximated quantum method (RPMD method) can be very efficient to determine thermalized rate constants and represents an interesting approach for many reactions in astro-chemistry. (author)