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Title: | Mechanisms of SiO oxidation: Implications for dust formation | Authors: | Andersson, Stefan Gobrecht, David Valero, Rosendo |
Keywords: | SiO; circumstellar; dust; DFT; rate coefficients; kinetics | Issue Date: | 9-Mar-2023 | Project: | Knut and Alice Wallenberg foundation (research grant KAW 2020.0081) | Serial title, monograph or event: | Frontiers in Astronomy and Space Sciences | Volume: | 10 | Abstract: | Reactions of SiO molecules have been postulated to initiate efficient formation of silicate dust particles in outflows around dying (AGB) stars. Both OH radicals and H$_2$O molecules can be present in these environments and their reactions with SiO and the smallest SiO cluster, Si$_2$O$_2$, affect the efficiency of eventual dust formation. Rate coefficients of gas-phase oxidation and clustering reactions of SiO, Si$_2$O$_2$ and Si$_2$O$_3$ have been calculated using master equation calculations based on density functional theory calculations. The calculations show that the reactions involving OH are fast. Reactions involving H$_2$O are not efficient routes to oxidation but may under the right conditions lead to hydroxylated species. The reaction of Si$_2$O$_2$ with H$_2$O, which has been suggested as efficient producing Si$_2$O$_3$, is therefore not as efficient as previously thought. If H$_2$O molecules dissociate to form OH radicals, oxidation of SiO and dust formation could be accelerated. Kinetics simulations of oxygen-rich circumstellar environments using our proposed reaction scheme suggest that under typical conditions only small amounts of SiO$_2$ and Si$_2$O$_2$ are formed and that most of the silicon remains as molecular SiO. | Description: | 10 pages, 13 figures | URI: | https://hdl.handle.net/10316/114747 | ISSN: | 2296-987X | DOI: | 10.3389/fspas.2023.1135156 | Rights: | openAccess |
Appears in Collections: | FCTUC Química - Artigos em Revistas Internacionais |
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Mechanisms of SiO oxidation Implications for dust formation.pdf | 2.33 MB | Adobe PDF | View/Open |
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