Chemical Transformations in the Inter-Stellar Medium: Photochemical Processes

Description du projet

Comprendre la formation des molécules dans le milieu interstellaire

Les premiers astronomes pensaient que le milieu interstellaire (MIS) était principalement constitué de matériaux ioniques et atomiques, ce qui rendait improbable la formation de molécules complexes. De récentes découvertes scientifiques révèlent cependant une région riche en grandes molécules complexes. Les conditions extrêmes de l’espace lointain forcent les réactions dans des états électroniques excités, générant des phénomènes moléculaires uniques. Les chercheurs peinent à expliquer cette formation, car ils ne disposent pas des outils modernes de la chimie quantique. Le projet AstroMol, financé par le CER, se propose de développer de nouveaux modèles théoriques. Il modélisera la dynamique des grosses molécules hautement excitées, telles que celles qui se trouvent dans le MIS, ce qui pourrait déboucher sur des percées en chimie computationnelle et améliorer notre compréhension du MIS.

Objectif

Until the beginning of the last century, the scientific convention was that the material in the interstellar medium (ISM) between stars and galaxies was mostly in atomic and ionic form thus the formation of complex molecules was improbable. Today, however, large complex molecules are being discovered at a dazzling rate demonstrating the molecular nature of our universe. The physical conditions in the ISM are extremely different than on Earth: in addition to extreme temperatures and low density, there are radiation fields, which, when interacting with atoms and molecules, result in unique chemistry occurring in excited electronic states. This interaction is responsible for many of the chemical phenomena observed in the ISM.
Currently, very little is known about the formation mechanisms of molecules in the ISM. The efforts to uncover the chemistry of the ISM are multidisciplinary, yielding experimental, observational, and theoretical results. Theoretical results are crucial for obtaining a molecular-level understanding of chemical phenomena theoretical results help to guide and decipher experimental and observational results. However, up to now, the toolkit of modern quantum chemistry cannot model the dynamic of large molecules in a highly excited electronic state. The aim of this proposed study is to fill this gap: I will develop new theoretical capabilities within quantum chemistry (specifically, ensemble density functional theory) that will enable us to model the dynamic of highly excited large molecules such as polyaromatic hydrocarbons (which play a crucial role in the chemical evolution of the ISM).
The ability to accurately model the dynamics of excited states will significantly advance the field of computational chemistry, giving it the ability to model systems that are currently outside its reach and provide a leap in our current understanding of the chemistry of the ISM.