Report on the outcomes of a Short-Term Scientific Mission

Action number: CA21101

Applicant name: Vincenzo Laporta

Details of the STSM

Title: The excitation of molecules in cometary comae

Start and end date: 02/10/2023 to 08/10/2023

Description of the work carried out during the STSM

During my stay at the Department of Physique of the University of Rennes, I had the opportunity to engage with Prof. F. Lique’s team and gain insights into their research focus. To present my previous work and scientific background to the team, I conducted a seminar.

The primary objective of my STSM internship was to initiate a collaborative effort on modelling the kinetics of radiation transfer in cometary comae. Notably, the rotational line emission from such rarefied atmospheres is significantly impacted by non-Boltzmann effects. This necessitates the application of non-local thermodynamic equilibrium (non-LTE) approaches to accurately interpret the abundant spectroscopic data collected from Solar System exospheres and plumes. These data are gathered through state-of-the-art ground and space-based facilities, including ALMA, JWST, and Rosetta telescopes.

To address this objective, thanks to some students of the team, I familiarized with the RADEX computer program, its implemented models, and the structure of its input and output files. RADEX is a non-LTE radiative transfer code founded on the principles of statistical equilibrium. It was originally developed by J. H. Black and employs an escape probability formulation under the assumption of an isothermal and homogeneous medium. Regarding collisional processes, I initially considered a model incorporating H2 and CS molecules. Subsequently, I extended the model to account for electron collisions.

Description of the STSM main achievements and planned follow-up activities

To provide more details, during my STSM visit at the University of Rennes, I utilized the RADEX code to assess the influence of molecular rotations on the spectral lines of CS molecules induced by electron impacts. This evaluation involved a comparison with results obtained in the absence of electrons. In pursuit of this objective, I conducted computations for state-specific cross sections and the corresponding rate constants, employing the Born approximation. The RADEX code was configured to simulate a mixture of H2 and CS molecules in the presence of an electron background.

Looking ahead, our investigations will expand to encompass variations in electron densities within the range of 10^-6 to 10^-3 times the density of H2 molecules, with H2 densities spanning from 10^4 to 10^6 cm^-3. Additionally, the gas’s translational temperature will be explored over the range of 50 to 200 K.

We believe that these findings hold a strong connection with the objectives outlined in the mission of Working Group 5 (WG5) within the COSY COST action, particularly concerning molecular systems of astrochemical significance in both gaseous and condensed phases, as well as the dynamics of reactions pertinent to spectroscopic and physical-chemical characterization.

The results from these studies will be disseminated through a forthcoming publication, and we intend to present them at an upcoming COSY General Meeting.

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