title: Ice chemistry

authors: Patrice Theule

abstract: Complex organic molecules (COMs) are widely observed in star-forming regions, although their formation mechanisms are not well understood. Solid-state chemistry occuring in the icy mantle of the interstellar grains is thought to play an important role, is poorly known.

In this contribution I will show how laboratory astrophysics is very instrumental to disentangle the different competing processes at work on interstellar grains. Experiments enables to measure reaction rate constants of isolated processes. This measured rates can then be incorporated in gas-grain models.

I will review recent works on purely thermal reactions involving species observed in ice astronomical spectra. I will emphasize the importance of the dynamics in chemistry. The dynamics is set first by the reaction rate constants and second by the diffusion coefficients of the reactants. I will show how it is possible to experimentally measured both reaction rate constants and diffusion coefficient in ice. I will also discuss how these measured parameters can be incorporated into gas-grain models, and what the problems inherent to the multilayer aspect of the ice mantle are.