Séminaire de l’équipe PCMT: Paul Pirlot Jankowiak (RIKEN Pioneering Research Institute)

Orateur : Paul Pirlot Jankowiak (Star and Planet Formation Laboratory, RIKEN Pioneering Research Institute (PRI), 2-1, Hirosawa, Wako, Saitama 351-0198, Japan)

Titre : Collisional excitation in space: from radicals to heavy molecules

Résumé :

The modeling and interpretation of molecular spectra from interstellar environments require the knowledge of both radiative and collisional processes of energy transfer between chemical species. Accurate state-to-state rate coefficients of interstellar molecules in collision with the main collisional partners H₂, H and He are then necessary. Such collisional data can be obtained through quantum time-independant scattering calculations by solving the close-coupled equations. This method is nowadays the most accurate for describing collisions at low temperature. However, such approach is not always applicable due to the complexity of molecular systems. One one hand, reactive systems like radicals must account for the interplay between inelastic and reactive processes when colliding with H and H₂, which remains a true theoretical challenge. On the other hand, some molecules are considered as ”heavy” when a large number of energy levels are necessary to describe state-to-state collisional cross sections, challenging the use of quantum methods in terms of computational time.

In this presentation, methodologies are proposed to overcome the different challenges related to reactive and heavy systems of astrophysical interest. These will be illustrated by the collisional excitation in the highly reactive OH⁺–H₂ system [1], and the case of collisions involving formaldehyde (H₂CO) isotopologues with H₂.

REFERENCES

[1] P. Pirlot Jankowiak & Lique, Phys. Rev. Lett. 134, 25300. DOI: 10.1103/hpcb-q7wh