Interstellar chemistry of gaz and grains

Chemical processes

A large part of the complexity of the medium originates in the complexity of its chemistry because molecular species contribute very specifically to the radiative cooling of the gas (depending on its density, temperature, etc.).

The chemical processes determine also the ionization degree of the neutral gas and therefore its coupling to the magnetic field. Dust particles of about 0.5 micron down to aggregates of only a few hundreds atoms and polycyclic-aromatic hydrocarbons play a major role in the energy exchanges between stellar radiation and gas.

Carbon chains formation

The formation of long chains (observed in the interstellar medium) and their link to the formation of nanoparticles and small solid particles (also observed in the medium) is being investigated on observational (molecular spectroscopy) and theoretical grounds in our group (D. Fossé & M. Gerin in collaboration with J. Cernicharo in Madrid)

Chemical bistability

Theoretical calculations have predicted a few years ago that the cold molecular gas might present chemical bistability, in regions where the ionization of the gas is not driven by UV photons but by cosmic rays. We have found observable signatures of the chemical bistability, an unexpected finding considering that each elemental gas volume evolves toward its own attractor at a specific rate.

Mixing of the different phases was therefore expected to blur any macroscopic signature of bistability on a given line of sight. The fact that it is not so opens new avenues (M. Gerin & E. Falgarone in collaboration with Paris Observatory).