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Title: Formation of silicon oxide grains at low temperature

The formation of grains in the interstellar medium, i.e., at low temperature, has been proposed as a possibility to solve the lifetime problem of cosmic dust. This process lacks a firm experimental basis, which is the goal of this study. We have investigated the condensation of SiO molecules at low temperature using neon matrix and helium droplet isolation techniques. The energies of SiO polymerization reactions have been determined experimentally with a calorimetric method and theoretically with calculations based on the density functional theory. The combined experimental and theoretical values have revealed the formation of cyclic (SiO) {sub k} (k = 2-3) clusters inside helium droplets at T = 0.37 K. Therefore, the oligomerization of SiO molecules is found to be barrierless and is expected to be fast in the low-temperature environment of the interstellar medium on the surface of dust grains. The incorporation of numerous SiO molecules in helium droplets leads to the formation of nanoscale amorphous SiO grains. Similarly, the annealing and evaporation of SiO-doped Ne matrices lead to the formation of solid amorphous SiO on the substrate. The structure and composition of the grains were determined by infrared absorption spectroscopy, transmission electron microscopy, and energy-dispersive X-ray spectroscopy. Ourmore » results support the hypothesis that interstellar silicates can be formed in the low-temperature regions of the interstellar medium by accretion through barrierless reactions.« less
Authors:
; ; ;  [1] ; ;  [2]
  1. Laboratory Astrophysics Group of the Max Planck Institute for Astronomy at the Friedrich Schiller University Jena, Institute of Solid State Physics, Helmholtzweg 3, D-07743 Jena (Germany)
  2. Max Planck Institute for Astronomy, Königstuhl 17, D-69117 Heidelberg (Germany)
Publication Date:
OSTI Identifier:
22348066
Resource Type:
Journal Article
Resource Relation:
Journal Name: Astrophysical Journal; Journal Volume: 782; Journal Issue: 1; Other Information: Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND SUPERFLUIDITY; ABSORPTION SPECTROSCOPY; ANNEALING; COSMIC DUST; DENSITY FUNCTIONAL METHOD; DOPED MATERIALS; DROPLETS; EVAPORATION; HELIUM; HYPOTHESIS; LIFETIME; MOLECULES; NANOSTRUCTURES; REFRACTORIES; SILICATES; SILICON OXIDES; SOLIDS; SURFACES; TRANSMISSION ELECTRON MICROSCOPY; X-RAY SPECTROSCOPY