Accurate determination of physical conditions of interstellar molecular clouds is a crucial step to better understand the life cycle of the interstellar matter and particularly the formation of stars and planets as well as the synthesis of organic molecules that may lead to emergence of life in the universe. A key parameter for the determination of these conditions from interstellar spectra is the calculation of accurate collisional rate coefficients of interstellar molecules with the most abundant species (H, He, H2 and e-).
Indeed, in order to make the most of the observational spectra, it is crucial to model the excitation conditions of the interstellar molecules that are primarily governed by collisional and radiative processes.
Whereas the knowledge of collisional processes has reached a certain level of maturity for collisions involving non-reactive molecules, very few reliable data exist for collisions involving reactive radicals and ions.
The computation of such data is a real challenge since inelastic and reactive processes compete during collisions.
The COLLEXISM project aims at overcoming this complex problem and to provide collisional data for these radicals and ions in order to derive as much information as possible from the molecular spectra collected by current telescopes.
As it is hardly possible to consider both collisional and reactive processes simultaneously, the COLLEXISM consortium will set up a new methodology based on quantum approach that allows obtaining accurate data. It will focus on molecular hydrides that are good candidates because of both their astrophysical importance and their quantum accessibility. The COLLEXISM consortium will carry out the determination of interaction potentials using quantum chemistry ab initio methods while the treatment of the dynamics of the nuclei will primarily be done using quantum time-independent reactive and non-reactive approaches. When exact quantum calculations will not be usable, innovative statistical quantum mechanical methods will also be explored.
The new data will then be used in radiative transfer models and the predictions will be finally compared to observations in order to derive the abundances of reactive radicals with unprecedented accuracy.
By providing, for the first time, collisional data for reactive systems, the present projects represents a major step forward in both the understanding of molecular energy transfer and the analysis of interstellar spectra.
