Grain Surface Reaction Dynamics from an Atomistic Perspecive

About 60 complex molecules have been observed in space. It is generally accepted that these are formed on the surface of dust grains in cold, dark regions of space. Here the grain acts both as an accretion spot for reactants and an energy sink for exothermic reactions. This concept forms the basis for theoretical models that are used in the interpretation of observational data in order to extract molecular details.

The dynamics of surface-reaction complexes are hitherto not considered in the application of such models. Previously, we showed that limited movement of reactants can yield non-reactive complexes that decrease reaction efficiency. Although, this effect is small for single-carbon baring species, we expect it to become more significant when larger species are considered.

Here we have used small molecules as a proxy to study the dynamics of reactants on cold grain surfaces. Metadynamics simulations give us binding sites that facilitate reactions. Using these binding sites we have simulated the meeting of small molecules on a surface. Finally, molecular dynamics simulations provided limits on the rearrangement of reactants in feasible binding sites. Altogether, these simulation results provide a clearer image of how species can meet on cold grain surfaces prior to reaction.