X-Ray-induced Photochemistry of Hydrocarbons: Implications for the Formation of Organic Haze in (Exo)Planetary Atmospheres
We present a laboratory study of X-ray-induced chemistry of organic molecules (CH _4 , C _2 H _4 , and C _2 H _6 ) irradiated with synchrotron X-rays in the 200–1000 eV range from the Advanced Light Source beamline 9.3.2 at the Lawrence Berkeley National Laboratory. Broadband nonmonochromated X-rays...
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2025-01-01
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| Online Access: | https://doi.org/10.3847/PSJ/adf4d3 |
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| author | Salma Bejaoui David Dubois Slavomir Nemsak Farid Salama |
| author_facet | Salma Bejaoui David Dubois Slavomir Nemsak Farid Salama |
| author_sort | Salma Bejaoui |
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| description | We present a laboratory study of X-ray-induced chemistry of organic molecules (CH _4 , C _2 H _4 , and C _2 H _6 ) irradiated with synchrotron X-rays in the 200–1000 eV range from the Advanced Light Source beamline 9.3.2 at the Lawrence Berkeley National Laboratory. Broadband nonmonochromated X-rays beams used in this study partially simulate X-rays emitted from low-mass young stellar objects (0.2–2 keV). The experiment is conducted by irradiating a vacuum chamber prefilled with the selected hydrocarbon at a pressure of 100 mTorr at room temperature during predefined exposure times of 5, 10, 20, and 30 minutes and 1 hr. After each exposure, the chemical photoproducts deposited on Si substrates are analyzed in situ using X-ray photoelectron spectroscopy (XPS). Secondary-ion mass spectrometry is also performed ex situ to determine the hydrogen content of the deposited samples. Our analysis indicates that the photoproducts formed from X-ray irradiation of C _2 H _4 undergo more extensive photoprocessing than those derived from CH _4 and C _2 H _6 . XPS results show that sp ^2 - and sp ^3 -fitted XPS bands correspond to amorphous carbon particles with hybridization that depends on the parent precursor molecules. When irradiating pure CH _4 , a fully sp ^3 -hybridized molecule, we found that X-ray photons induce photochemical reactions leading to the formation of heavier organics with sp ^2 C=C bonds. Possible chemical pathways and astrophysical implications are discussed. |
| format | Article |
| id | doaj-art-78db1fda57b3467e97461fb6d766ec96 |
| institution | Kabale University |
| issn | 2632-3338 |
| language | English |
| publishDate | 2025-01-01 |
| publisher | IOP Publishing |
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| series | The Planetary Science Journal |
| spelling | doaj-art-78db1fda57b3467e97461fb6d766ec962025-08-26T06:25:34ZengIOP PublishingThe Planetary Science Journal2632-33382025-01-016820310.3847/PSJ/adf4d3X-Ray-induced Photochemistry of Hydrocarbons: Implications for the Formation of Organic Haze in (Exo)Planetary AtmospheresSalma Bejaoui0https://orcid.org/0000-0001-8646-9464David Dubois1https://orcid.org/0000-0001-6754-8933Slavomir Nemsak2https://orcid.org/0000-0002-6103-2925Farid Salama3https://orcid.org/0000-0002-6064-4401Space Science & Astrobiology Division, NASA Ames Research Center , Moffett Field, CA 94035, USA; Bay Area Environmental Research Institute , Moffett Field, CA 95476, USASpace Science & Astrobiology Division, NASA Ames Research Center , Moffett Field, CA 94035, USA; Bay Area Environmental Research Institute , Moffett Field, CA 95476, USAAdvanced Light Source, Lawrence Berkeley National Laboratory , Berkeley, CA 94720, USA; Department of Physics and Astronomy, University of California , Davis, CA 95616, USASpace Science & Astrobiology Division, NASA Ames Research Center , Moffett Field, CA 94035, USAWe present a laboratory study of X-ray-induced chemistry of organic molecules (CH _4 , C _2 H _4 , and C _2 H _6 ) irradiated with synchrotron X-rays in the 200–1000 eV range from the Advanced Light Source beamline 9.3.2 at the Lawrence Berkeley National Laboratory. Broadband nonmonochromated X-rays beams used in this study partially simulate X-rays emitted from low-mass young stellar objects (0.2–2 keV). The experiment is conducted by irradiating a vacuum chamber prefilled with the selected hydrocarbon at a pressure of 100 mTorr at room temperature during predefined exposure times of 5, 10, 20, and 30 minutes and 1 hr. After each exposure, the chemical photoproducts deposited on Si substrates are analyzed in situ using X-ray photoelectron spectroscopy (XPS). Secondary-ion mass spectrometry is also performed ex situ to determine the hydrogen content of the deposited samples. Our analysis indicates that the photoproducts formed from X-ray irradiation of C _2 H _4 undergo more extensive photoprocessing than those derived from CH _4 and C _2 H _6 . XPS results show that sp ^2 - and sp ^3 -fitted XPS bands correspond to amorphous carbon particles with hybridization that depends on the parent precursor molecules. When irradiating pure CH _4 , a fully sp ^3 -hybridized molecule, we found that X-ray photons induce photochemical reactions leading to the formation of heavier organics with sp ^2 C=C bonds. Possible chemical pathways and astrophysical implications are discussed.https://doi.org/10.3847/PSJ/adf4d3Astrochemistry |
| spellingShingle | Salma Bejaoui David Dubois Slavomir Nemsak Farid Salama X-Ray-induced Photochemistry of Hydrocarbons: Implications for the Formation of Organic Haze in (Exo)Planetary Atmospheres The Planetary Science Journal Astrochemistry |
| title | X-Ray-induced Photochemistry of Hydrocarbons: Implications for the Formation of Organic Haze in (Exo)Planetary Atmospheres |
| title_full | X-Ray-induced Photochemistry of Hydrocarbons: Implications for the Formation of Organic Haze in (Exo)Planetary Atmospheres |
| title_fullStr | X-Ray-induced Photochemistry of Hydrocarbons: Implications for the Formation of Organic Haze in (Exo)Planetary Atmospheres |
| title_full_unstemmed | X-Ray-induced Photochemistry of Hydrocarbons: Implications for the Formation of Organic Haze in (Exo)Planetary Atmospheres |
| title_short | X-Ray-induced Photochemistry of Hydrocarbons: Implications for the Formation of Organic Haze in (Exo)Planetary Atmospheres |
| title_sort | x ray induced photochemistry of hydrocarbons implications for the formation of organic haze in exo planetary atmospheres |
| topic | Astrochemistry |
| url | https://doi.org/10.3847/PSJ/adf4d3 |
| work_keys_str_mv | AT salmabejaoui xrayinducedphotochemistryofhydrocarbonsimplicationsfortheformationoforganichazeinexoplanetaryatmospheres AT daviddubois xrayinducedphotochemistryofhydrocarbonsimplicationsfortheformationoforganichazeinexoplanetaryatmospheres AT slavomirnemsak xrayinducedphotochemistryofhydrocarbonsimplicationsfortheformationoforganichazeinexoplanetaryatmospheres AT faridsalama xrayinducedphotochemistryofhydrocarbonsimplicationsfortheformationoforganichazeinexoplanetaryatmospheres |