High-temperature measurements of acetylene VUV absorption cross sections and application to warm exoplanet atmospheres
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| Format: | Preprint |
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2025
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| author | Fleury, Benjamin Poveda, Mathilde Benilan, Yves Veillet, Roméo Venot, Olivia Tremblin, Pascal Fray, Nicolas Gazeau, Marie-Claire Schwell, Martin Jolly, Antoine de Oliveira, Nelson Es-sebbar, Et-touhami |
| author_facet | Fleury, Benjamin Poveda, Mathilde Benilan, Yves Veillet, Roméo Venot, Olivia Tremblin, Pascal Fray, Nicolas Gazeau, Marie-Claire Schwell, Martin Jolly, Antoine de Oliveira, Nelson Es-sebbar, Et-touhami |
| contents | Most observed exoplanets have high equilibrium temperatures. Understanding the chemistry of their atmospheres and interpreting their observations requires the use of chemical kinetic models including photochemistry. The thermal dependence of the vacuum ultraviolet (VUV) absorption cross sections of molecules used in these models is poorly known at high temperatures, leading to uncertainties in the resulting abundance profiles. The aim of our work is to study experimentally the thermal dependence of VUV absorption cross sections of molecules of interest for exoplanet atmospheres and provide accurate data for use in atmospheric models. This study focuses on acetylene (C2H2). We measured absorption cross sections of C2H2 at seven temperatures ranging from 296 to 773 K recorded in the 115-230 nm spectral domain using VUV spectroscopy and synchrotron radiation. These data were used in our 1D thermo-photochemical model, to assess their impact on the predicted composition of a generic hot Jupiter-like exoplanet atmosphere. The absolute absorption cross sections of C2H2 increase with temperature. This increase is relatively constant from 115 to 185 nm and rises sharply from 185 to 230 nm. The abundance profile of C2H2 calculated using the model shows a slight variation, with a maximum decrease of 40% near 5 x 10-5 bar, when using C2H2 absorption cross sections measured at 773 K compared to those at 296 K. This is explained by the absorption, higher in the atmosphere, of the actinic flux from 150 to 230 nm due to the increase in the C2H2 absorption in this spectral range. This change also impacts the abundance profiles of other by-products such as methane (CH4) and ethylene (C2H4). We present the first experimental measurements of the VUV absorption cross sections of C2H2 at high temperatures. Similar studies of other major species are needed to improve our understanding of exoplanet atmospheres. |
| format | Preprint |
| id |
arxiv_https___arxiv_org_abs_2501_02864 |
| institution | arXiv |
| publishDate | 2025 |
| record_format | arxiv |
| spellingShingle | High-temperature measurements of acetylene VUV absorption cross sections and application to warm exoplanet atmospheres Fleury, Benjamin Poveda, Mathilde Benilan, Yves Veillet, Roméo Venot, Olivia Tremblin, Pascal Fray, Nicolas Gazeau, Marie-Claire Schwell, Martin Jolly, Antoine de Oliveira, Nelson Es-sebbar, Et-touhami Earth and Planetary Astrophysics Most observed exoplanets have high equilibrium temperatures. Understanding the chemistry of their atmospheres and interpreting their observations requires the use of chemical kinetic models including photochemistry. The thermal dependence of the vacuum ultraviolet (VUV) absorption cross sections of molecules used in these models is poorly known at high temperatures, leading to uncertainties in the resulting abundance profiles. The aim of our work is to study experimentally the thermal dependence of VUV absorption cross sections of molecules of interest for exoplanet atmospheres and provide accurate data for use in atmospheric models. This study focuses on acetylene (C2H2). We measured absorption cross sections of C2H2 at seven temperatures ranging from 296 to 773 K recorded in the 115-230 nm spectral domain using VUV spectroscopy and synchrotron radiation. These data were used in our 1D thermo-photochemical model, to assess their impact on the predicted composition of a generic hot Jupiter-like exoplanet atmosphere. The absolute absorption cross sections of C2H2 increase with temperature. This increase is relatively constant from 115 to 185 nm and rises sharply from 185 to 230 nm. The abundance profile of C2H2 calculated using the model shows a slight variation, with a maximum decrease of 40% near 5 x 10-5 bar, when using C2H2 absorption cross sections measured at 773 K compared to those at 296 K. This is explained by the absorption, higher in the atmosphere, of the actinic flux from 150 to 230 nm due to the increase in the C2H2 absorption in this spectral range. This change also impacts the abundance profiles of other by-products such as methane (CH4) and ethylene (C2H4). We present the first experimental measurements of the VUV absorption cross sections of C2H2 at high temperatures. Similar studies of other major species are needed to improve our understanding of exoplanet atmospheres. |
| title | High-temperature measurements of acetylene VUV absorption cross sections and application to warm exoplanet atmospheres |
| topic | Earth and Planetary Astrophysics |
| url | https://arxiv.org/abs/2501.02864 |