Silicon and Hydrogen Chemistry under Laboratory Conditions Mimicking the Atmosphere of Evolved Stars

Abstract

Silicon is present in interstellar dust grains, meteorites and asteroids, and to date 13 silicon-bearing molecules have been detected in the gas phase toward late-type stars or molecular clouds, including silane and silane derivatives. In this work, we have experimentally studied the interaction between atomic silicon and hydrogen under physical conditions mimicking those in the atmosphere of evolved stars. We have found that the chemistry of Si, H, and H2 efficiently produces silane (SiH4), disilane (Si2H6) and amorphous hydrogenated silicon (a-Si:H) grains. Silane has been definitely detected toward the carbon-rich star IRC +10216, while disilane has not been detected in space yet. Thus, based on our results, we propose that gas-phase reactions of atomic Si with H and H2 are a plausible source of silane in C-rich asymptotic giant branch stars, although its contribution to the total SiH4 abundance may be low in comparison with the suggested formation route by catalytic reactions on the surface of dust grains. In addition, the produced a-Si:H dust analogs decompose into SiH4 and Si2H6 at temperatures above 500 K, suggesting an additional mechanism of formation of these species in envelopes around evolved stars. We have also found that the exposure of these dust analogs to water vapor leads to the incorporation of oxygen into Si–O–Si and Si–OH groups at the expense of SiH moieties, which implies that if this kind of grain is present in the interstellar medium, it will probably be processed into silicates through the interaction with water ices covering the surface of dust grains.

Hydrogenated Silicon Nanoclusters with a Permanent Electric Dipole Moment for the Controlled Assembly of Silicon-Based Nanostructures

“…Silicon nanoclusters (SiNCs) and nanoparticles (SiNPs) have continuously attracted state-of-the-art research for several decades because of their interest for micro- and nanoelectronics. , Despite worldwide and intensive exploration, however, those nano-entities of silicon keep providing surprises when unveiling even more of their secrets. Some of the most recent research topics concern, for instance, hydrogen generation via mesoporous SiNP photocatalyst and via oxidation of hydrogenated SiNCs; therapeutic potentials of transferrin-functionalized porous SiNPs against glioma cell migration in brain tumor treatment; facile procedure for the synthesis of ultrafine SiNPs; isolable unsaturated silicon clusters; − production of unoxidized, hydrogenated, and amorphous SiNPs using ultrasonic technologies; improved understanding of interstellar dust grains, meteorites, and asteroids; functional nanophotonics; exploration of unusual size dependence of electronic and optical absorption gaps of hydrogenated SiNPs; and deposition of hydrogenated SiNCs for efficient epitaxial growth …”

Impact of Metals on (Star)Dust Chemistry: A Laboratory Astrophysics Approach

“…In the spectrum of the Agcontaining sample (P1), the band shape has changed with a maximum of the band at 2,153 cm −1 . The position and shape of the SiH band are found to depend on the chemical environment of the grain (Moore et al, 1991) and also on the gas-phase environment through gas-grain interactions (Accolla et al, 2021). The observed variations could therefore be attributed to this effect.…”

Impact of metals on (star)dust chemistry: a laboratory astrophysics approach

“…In the spectrum of the Ag-containing sample (P1), the band shape has changed with a maximum of the band at 2153 cm −1 . The position and shape of the SiH band are found to depend on the chemical environment of the grain (Moore et al, 1991) and also on the gas-phase environment through gas-grain interactions (Accolla et al, 2021). The observed variations could therefore be attributed to this effect.…”