21-EPN-FT1-015: Characterising electron impact induced UV-Optical emission of simple molecules relevant to atmospheres of small Solar System bodies

Visit by Steven Bromley, Auburn University (USA), to TA2 Facility 13 – Electron Induced Fluorescence Laboratory (Slovakia).
Dates of visit: 25 July – 08 August 2022

Report Summary: The goal of the 2022 visit was to study and measure the electron-impact induced emission from dissociation and/or ionisation of CO and CO₂ between 0 – 100 eV electron energy. These experiments are part of a longer-term plan to characterize the electron-impact-induced emission features of oxygen-containing molecules found in cometary environments. These data are expected to be used in future modelling and analyses of data acquired in situ during the Rosetta mission to comet 67P/Churyumov-Gerasimenko. We aim to understand the conditions in the inner coma and how electron-impact-induced emission features can probe the physical and chemical processes occurring in the near-nucleus coma environment.  

During the first half of the visit, we measured electron-impact spectra of CO₂ gas at multiple electron energies. Electron impact of CO₂ can give rise to emission from CO, CO⁺, CO₂⁺, and excited states of C and O atoms. Since the probabilities of the different reaction channels depend strongly on the collision energy, these spectral features offer a way to diagnose the conditions of plasmas containing CO₂. The collected spectra and threshold measurements are in reasonable agreement with the limited data in the literature. During the second half of the visit, we measured electron-impact spectra of CO gas at numerous electron energies. Many of the spectral features for neutral CO, CO⁺, and atomic C and O were characterised, as a function of electron energy, for the first time. Given the time-consuming nature of the measurements, data analysis and additional measurements will continue remotely. 

Read the full scientific report, with kind permission by Steve Bromley.

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