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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| Main Authors: | , , , |
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| Format: | Article |
| Language: | English |
| Published: |
IOP Publishing
2025-01-01
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| Series: | The Planetary Science Journal |
| Subjects: | |
| Online Access: | https://doi.org/10.3847/PSJ/adf4d3 |
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| Summary: | 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. |
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| ISSN: | 2632-3338 |