ANR CECoSA project led by L. Rutkowski (IPR)

Frequency comb cavity spectroscopy for astrophysics

The objective of the CECoSA project is to use mid-infrared optical frequency comb spectroscopy combined with the CRESU (Reactional Kinetics in Uniform Supersonic Flows) technique to perform time-resolved diagnosis of low-temperature reactions involving radicals.
Radicals are essential in astrochemistry as they are the cornerstone of the formation of complex species such as polycyclic aromatic hydrocarbons (PAHs) or complex organic molecules (COMs), whose presence in the interstellar medium has been observed and whose formation processes are still poorly understood. Understanding the kinetics and pathways of these fundamental processes is vital for modelling the physical chemistry of planetary atmospheres and interstellar clouds. It requires extensive laboratory studies at temperatures corresponding to those of extraterrestrial atmospheres, such as Titan (70-150 K), or interstellar clouds (10-100 K). In particular, reactions between radicals play a predominant role at low temperatures since this interaction can generate multiple potential energy surfaces (PES) correlated adiabatically with the reactants, thus multiple exit routes. In order to quantify them, it is necessary to detect the formation of all products.
The CRESU technique is the technique of choice to carry out these kinetic studies as it can probe gaseous samples at temperatures ranging from 13 to 150 K. However, probing the molecular processes taking place in these flows requires a fast, quantitative, sensitive and multi-species detection technique. Optical frequency comb spectroscopy used as a diagnostic in CRESU offers all these advantages in a single measurement, and opens the way to the simultaneous detection of reactant consumption rates, formation rates of different products, as well as possible intermediate complexes.
The CECoSA project will carry out ambitious experimental developments, combining for the first time mid-infrared optical combs, optical cavities and ultrafast Fourier transform spectroscopy, making it possible to follow the evolution of chemical reactions with the necessary sensitivity and speed. This instrument will be the first diagnostic tool based on frequency combs operating in uniform supersonic flows. It will be used to answer key scientific questions in the field of astrochemistry. In particular, it will target radical-radical reactions, which represent a major experimental challenge.