Abstract:

The chemical reactions occurring in the astrophysical context are at the origin of the molecular complexity observed in these environments[1]. These chemical reactions are characterised by their thermal rate constants, which can be theoretically determined with quantum dynamics simulations. State-of-the-art, in quantum dynamics methods, remains the Close-Coupling approach[2-3] but is mainly limited to triatomic species (due to their computational cost) and requires a global potential energy surface. Although very accurate, this method is not suitable for more complex molecular systems and new computational methods, approximated but accurate, are needed. We propose a new set of curvilinear coordinates transformations[4] that enable us to perform quantum dynamics simulations following a minimum energy path. This approach do not require a full global potential energy surface calculation. This set of curvilinear coordinates are combined with a direct determination of the thermal rate constant using the Green's operator formulation with complex absorbing potentials[5] avoiding the full S-matrix computation. The efficiency of this new scheme is demonstrated on the collinear chemical reaction H + H2 → H2 + H for which accurate close-coupling results are available [6,7]. Furthermore, our computational scheme can be efficiently combined with a reduced dimensional model for complex chemical reactions.