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Journal Articles Monthly Notices of the Royal Astronomical Society Year : 2024

Heavy ion radiolysis of the chiral terpene $\alpha$-pinene

Abstract

Radiolysis of α-pinene by 61.3 MeV $^{84}$Kr$^{15+}$ ions was analyzed with the scope to simulate the effects of heavy ion cosmic ray bombardment on chiral molecules in typical interstellar medium. The α-pinene ice samples were irradiated at 10 K and their chemical evolution was monitored by mid-infrared Fourier transform (FTIR) spectroscopy to characterize the reaction products and to determine the extent of racemization. The integrated band strengths have been obtained for all the neutral α-pinene vibrational bands using the experimental band integrated absorbances and the theoretical absolute intensities calculated along the column densities. In the current heavy ion bombardment experiments, small molecules were formed and the precursor, α-pinene, was destroyed instead of being racemized. Twelve hydrocarbons were produced (final fluence of 2.0 × 10$^{12}$ ions.cm$^{-2}$): methane (CH$_4$), acetylene (C$_2$H$_2$), ethylene (C$_2$H$_4$), propylene (C$_3$H$_6$), propane (C$_3$H$_8$), n-butane (C$_4$H$_{10}$), butene (C$_4$H$_8$), propyne (C$_3$H$_4$), benzene (C$_6$H$_6$), ethane (C$_2$H$_6$), vinylacetylene (C$_4$H$_4$) and 2-methyl-1,3-butadiene or isoprene (C$_5$H$_8$). The highest formation cross section (∼ 40 × 10$^{−15}$ cm$^2$) was observed for the C$_3$H$_4$ and the lowest was for C$_3$H$_8$ (∼ 3 × 10$^{−15}$ cm$^2$). The radiochemical yields for these molecules follow the same trends as those of their cross sections. The atom budget calculation confirms that all the expected products have been generated during the radiolysis and supports the conclusion that the proposed A-values are accurate. The α-pinene sputtering yield for this ion beam was found to be Y$_0$ = 1.84 × 10$^6$ molecules per impact.
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Dates and versions

hal-04516709 , version 1 (22-03-2024)

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A L. F. de Barros, A. Ricca, A. Bychkova, C A. P. da Costa, J. W. Costa, et al.. Heavy ion radiolysis of the chiral terpene $\alpha$-pinene. Monthly Notices of the Royal Astronomical Society, 2024, pp.stae757. ⟨10.1093/mnras/stae757⟩. ⟨hal-04516709⟩
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