Towards a mechanism for formation of silicon carbide crystals in AGB stars

Lutz, Jesse J.

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https://hdl.handle.net/2142/104458 Copy

Description

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.

Issue Date

2019-06-19

Keyword(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.

Publisher

International Symposium on Molecular Spectroscopy

Type of Resource

text

Language

eng

Permalink

http://hdl.handle.net/2142/104458

DOI

https://doi.org/10.15278/isms.2019.WA02

Copyright and License Information

Copyright 2019 Jesse J. Lutz

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