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Title:TOWARDS A MECHANISM FOR FORMATION OF SILICON CARBIDE CRYSTALS IN AGB STARS
Author(s):Lutz, Jesse J
Contributor(s):Burggraf, Larry W; Duan, Xiaofeng F
Subject(s):Astronomy
Abstract:Silicon carbide (SiC) grains comprise a significant fraction of the dust found around carbon-rich AGB stars. Their presence in the interstellar medium is thought to originate from self-assembly of organosilicon building blocks, including previously observed species such as carborundum and cyclic silicon dicarbide ({\it c}-SiC$_2$). However, the actual formation mechanisms of even these simple silicon-bearing organic molecules remains elusive. Here it is proposed that disilyne (Si$_2$H$_2$) reacts barrierlessly with abundant acetylene (C$_2$H$_2$) on a spin-conserving potential to form C$_2$Si$_2$H$_4$. This species has been shown in experimental and theoretical studies\footnote{Lutz J.J., Inorganics, {\it submitted}} to photoisomerize under UV irradiation resulting in the formation of several species, one being a {\it c}-SiC$_2$ precursor and another being a highly polar species capable of supporting a dipole-bound electron. This strongly dipolar C$_2$Si$_2$H$_4$ isomer may represent the missing link supporting the molecular aggregation hypothesis for SiC formation. Importantly, its polarity drives molecular aggregation, and, after subsequent oxidation to C$_2$Si$_2$, its heteronuclear linkages are well-prepared for SiC nucleation, presumably initiated by a shock-wave pulsation event. Past theoretical studies by our group\footnote{Lutz J.J., Duan X.F., et al. J. Chem. Phys. 148, 174309 (2018)}\footnote{Byrd J.N., Lutz J.J., et al. J. Chem. Phys. 145, 024312 (2016)} are combined with new results, computed at the DFT and coupled-cluster levels of theory, to support the proposed mechanism.
Issue Date:2019-06-19
Publisher:International Symposium on Molecular Spectroscopy
Genre:Conference Paper / Presentation
Type:Text
Language:English
URI:http://hdl.handle.net/2142/104458
DOI:10.15278/isms.2019.WA02
Rights Information:Copyright 2019 Jesse J Lutz
Date Available in IDEALS:2019-07-15
2020-01-25


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