Please use this identifier to cite or link to this item:
Title: Nucleation of small silicon carbide dust clusters in AGB stars
Author: Gobrecht, David
Cristallo, Sergio
Piersanti, Luciano
Bromley, Stefan Thomas
Keywords: Estels
Pols còsmica
Cosmic dust
Issue Date: 10-May-2017
Publisher: Institute of Physics (IOP)
Abstract: Silicon carbide (SiC) grains are a major dust component in carbon-rich asymptotic giant branch stars. However, the formation pathways of these grains are not fully understood. We calculate ground states and energetically low-lying structures of (SiC)(n), n = 1, 16 clusters by means of simulated annealing and Monte Carlo simulations of seed structures and subsequent quantum-mechanical calculations on the density functional level of theory. We derive the infrared (IR) spectra of these clusters and compare the IR signatures to observational and laboratory data. According to energetic considerations, we evaluate the viability of SiC cluster growth at several densities and temperatures, characterizing various locations and evolutionary states in circumstellar envelopes. We discover new, energetically low-lying structures for Si4C4, Si5C5, Si15C15, and Si16C16 and new ground states for Si10C10 and Si15C15. The clusters with carbon-segregated substructures tend to be more stable by 4-9 eV than their bulk-like isomers with alternating Si-C bonds. However, we find ground states with cage geometries resembling buckminsterfullerens ('bucky-like') for Si12C12 and Si16C16 and low-lying stable cage structures for n >= 12. The latter findings thus indicate a regime of cluster sizes that differ from small clusters as well as from large-scale crystals. Thus-and owing to their stability and geometry-the latter clusters may mark a transition from a quantum-confined cluster regime to a crystalline, solid bulk-material. The calculated vibrational IR spectra of the ground-state SiC clusters show significant emission. They include the 10-13 mu m wavelength range and the 11.3 mu m feature inferred from laboratory measurements and observations, respectively, although the overall intensities are rather low.
Note: Reproducció del document publicat a:
It is part of: Astrophysical Journal, 2017, vol. 840, num. 2
Related resource:
ISSN: 0004-637X
Appears in Collections:Articles publicats en revistes (Ciència dels Materials i Química Física)

Files in This Item:
File Description SizeFormat 
673210.pdf4 MBAdobe PDFView/Open

Items in DSpace are protected by copyright, with all rights reserved, unless otherwise indicated.