Solid interstellar radical chemistry – SIRC

One of the major questions in modern physics is how life emerged on Earth and whether it is a general characteristic of our Universe. In addition to its own interest, understanding molecular complexity in space helps to understand the link between the young Solar System and its small bodies, in which today we detect complex molecules and even amino acids (as in comets and meteorites). Where these molecules come from? How and where did they form? What do they tell us about stars and planets formation? And last, but not least, atoms and molecules are the remote thermometers and barometers, as their observed line spectra can and are used to extract a mine of precious and often unique information.
Grain-surface astrochemistry is facing new fascinating and challenging questions. Among them, three are particularly relevant for this project:
- Is it possible to build a grain-surface chemistry starting from radical blocks, and if so, what will be the chemical routes?
- Is the diffusion of radicals fast enough to compete with atom addition (and destruction)?
- How to measure radicals in experiments, in realistic conditions ?
- Is grain-surface chemistry fully compatible with the astronomical observations and the current astrochemical models? Or in other words, what ISM molecules form prevalently on the grain surfaces and when?

Here we propose to join the forces between two groups with complementary laboratory expertise (LERMA and PIIM) and one with astrophysical, observations and modeling, expertise (IPAG).
The immediate project goal is to understand how molecules diffuse, meet and mate on the grain surfaces in order to assess what COMs are formed on them and how. To reach it, we will compare dedicated laboratory experiments and include them in a new astrochemical code able, at the end of the project, to compare predictions with observations, and to better understand the role and limits of the solid-state chemistry in space.
The work is organized in 3 connected tasks corresponding of our 3 expertises :
1) Diffusion of radicals and building-up molecules on surfaces. It includes i) the optimization of new source of radicals and the measurement of their diffusions ii) the systematic studies of the reactivity of specific chemical groups iii) in order to understand what is the limit of the complexity of COMs synthesized on surfaces
2) An innovative experimental set-up will be implemented at PIIM coupling low-temperature chemistry and electron spin resonance (ESR) to overcome our blindness to intermediate species. Once done, slow reactivity of radical with their molecular environment will be studied, simulating the early stage of ice mantle growth. The final goal is to study radical-radical chemistry that should occur during the formation of stars
3) We will build up a new code, from GRAINOBLE, that is able to simulate the experimental results. Only after this first step, it will be possible to extrapolate the experimental results to the ISM conditions, as well as having a better determination of physical parameters to be included in astrochemical codes.
The natural end of this project will be to compare our understanding of the solid-state chemistry to observations, to evaluate its impact on the molecular growth and to diffuse our results.