Silicon Oxide Nanoparticles Reveal the Origin of Silicate Grains in Circumstellar Environments

Abstract

A synergistic effort combining experiments in beams and first principles theoretical investigations is used to propose mechanisms that could lead to the formation of silicates and nanoparticles with silicon-rich cores through agglomeration of SiO, an abundant oxygen-bearing species in space. The silicon oxygen species involved in the transformation have optical excitations that could contribute to extended red emissions and blue luminescence. Apart from resolving an outstanding astronomical problem, we demonstrate novel silicon architectures.

The oxygen isotope effect in the earliest processed solids in the solar system: is it a chemical mass-independent process?

“…There is a substantial decrease in intensity in going from n = 3 to n = 4, and there is also a marked increase in intensity in going from n = 6 to n = 7. The experimental observation of intensity distributions of clusters (SiO) n is consistent with the calculated (Reber et al 2006) intrinsic binding stability of their ground state structures. The gradient corrected density functional theoretical studies (Reber et al 2006) on the geometry, electronic structure and stability of clusters suggest that (SiO) n clusters containing up to 4 units are single rings.…”

“…The experimental observation of intensity distributions of clusters (SiO) n is consistent with the calculated (Reber et al 2006) intrinsic binding stability of their ground state structures. The gradient corrected density functional theoretical studies (Reber et al 2006) on the geometry, electronic structure and stability of clusters suggest that (SiO) n clusters containing up to 4 units are single rings. The Si-Si bond appears first at Si 5 O 5 , and starting at this size, the elementary rings begin to assemble into multiple rings that eventually lead to cages.…”

“…We will present three key arguments -based on recent laboratory experimental findings (Reber et al 2006) of the compositional distributions of cluster intermediates during nucleation of SiO, the first principles density functional theoretical interpretation (Reber et al 2006) of their growth mechanisms, and astronomical observations of silicate formation in planet-forming circumstellar disks (van Boekel et al 2004). What follows will show that the "slope1" oxygen isotopic distributions are due to non-RRKM effect in unimolecular steps in bimolecular reactions during SiO 2 formation on the surface of a growing cluster.…”

“…Table 1 represents the relative intensities of the clusters (SiO) n (SiO 2 ) m shown in Fig. 1 in Reber et al (2006). These clusters form from SiO molecules laser-vaporized from SiO solid under a helium atmosphere.…”

“…To reach the energetically most stable configuration of a cluster of a given size, atomic oxygen must be transported from the core to the interface of silicon atoms in Fig. 2 in reference (Reber et al 2006). We refer the oxygen atoms on the Si-rich surface as adsorbates or O(ads) in the discussion that follows.…”