Issue |
A&A
Volume 691, November 2024
|
|
---|---|---|
Article Number | A209 | |
Number of page(s) | 9 | |
Section | Interstellar and circumstellar matter | |
DOI | https://doi.org/10.1051/0004-6361/202451474 | |
Published online | 15 November 2024 |
The effect of dilution on the energy dissipation in water interstellar ice analogues
Probed by infrared irradiation
1
HFML-FELIX laboratory, IMM, Radboud University,
Toernooiveld 7,
6525 ED
Nijmegen,
The Netherlands
2
Institute of Molecules and Materials (IMM), Radboud University,
Heyendaalseweg 135,
6525 AJ
Nijmegen,
The Netherlands
3
Centre for Interstellar Catalysis (InterCat), Department of Physics and Astronomy, University of Aarhus,
Aarhus
8000,
Denmark
★ Corresponding author; h.cuppen@science.ru.nl
Received:
12
July
2024
Accepted:
12
September
2024
Context. Interstellar ices and their energetic processing play an important role in advancing the chemical complexity in space. Interstellar ices covering dust grains are intrinsically mixed, and it is assumed that physicochemical changes induced by energetic processing – triggered by photons, electrons, and ions – strongly depend on the content of the ice. Yet, the modelling of these complex mixed systems in experiments and theory is complicated.
Aims. In this paper, we investigate the effect of infrared irradiation on a series of different molecules mixed with porous amorphous solid water (pASW) to study the release of vibrational energy in the hydrogen-bonding network of water as a function of mixing ratio and ice content. Particularly, we select mixtures of 20:1 H2O:X and 5:1 H2O:X with X=CO2, NH3, or CH4.
Methods. Infrared radiation was supplied by the intense and tunable free electron laser (FEL) 2 at the HFML-FELIX facility. We monitored the structural changes in the interstellar ice analogue after resonant infrared excitation using Fourier-transform reflection absorption infrared (FT-RAIR) spectroscopy.
Results. We observed that on-resonance irradiation at the OH-stretching vibration of pASW results in quantitatively identical changes compared to pure pASW for all investigated mixtures. The structural changes we observed closely resemble the previously reported local reordering. The 5:1 mixtures show weaker changes compared to pure pASW, with a decrease in strength from NH3 to CO2.
Conclusions. Since the hydrogen-bonding network of pASW restructures similarly upon FEL irradiation, regardless of the mixing component, treating ice layers in models that simulate energy dissipation in the hydrogen-bonding network as pure H2O ice layers can be a justified approximation. Hence, complex systems might not always be necessary to describe the infrared energetic processing of ices.
Key words: astrochemistry / molecular processes / methods: laboratory: solid state / ISM: molecules / infrared: ISM
© The Authors 2024
Open Access article, published by EDP Sciences, under the terms of the Creative Commons Attribution License (https://creativecommons.org/licenses/by/4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
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