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

Abstract

Laboratory experiments are essential in exploring the mechanisms involved in stardust formation. One key question is how a metal is incorporated into dust for an environment rich in elements involved in stardust formation (C, H, O, Si). To address experimentally this question we have used a radiofrequency cold plasma reactor in which cyclic organosilicon dust formation is observed. Metallic (silver) atoms were injected in the plasma during the dust nucleation phase to study their incorporation in the dust. The experiments show formation of silver nanoparticles (~15 nm) under conditions in which organosilicon dust of size 200 nm or less is grown. The presence of AgSiO bonds, revealed by infrared spectroscopy, suggests the presence of junctions between the metallic nanoparticles and the organosilicon dust. Even after annealing we could not conclude on the formation of silver silicates, emphasizing that most of silver is included in the metallic nanoparticles. The molecular analysis performed by laser mass spectrometry exhibits a complex chemistry leading to a variety of molecules including large hydrocarbons and organometallic species. In order to gain insights into the involved chemical molecular pathways, the reactivity of silver atoms/ions with acetylene was studied in a laser vaporization source. Key organometallic species, AgnC2Hm (n = 1–3; m = 0–2), were identified and their structures and energetic data computed using density functional theory. This allows us to propose that molecular Ag–C seeds promote the formation of Ag clusters but also catalyze hydrocarbon growth. Throughout the article, we show how the developed methodology can be used to characterize the incorporation of metal atoms both in the molecular and dust phases. The presence of silver species in the plasma was motivated by objectives finding their application in other research fields than astrochemistry. Still, the reported methodology is a demonstration laying down the ground for future studies on metals of astrophysical interest, such as iron.

Layer-by-layer structured nanocomposite deposits from plasma-synthesized organosilicon nanoparticles and organosilicon nanoparticles decorated with Ag nanoparticles by taking advantage of cyclic nanoparticle formation in Ar/HMDSO reactive plasmas

“…The plateau in the AgI line intensity suggests an additional source of release of Ag atoms into the plasma compared to the silver sputtering from the target since the electron temperature is decreasing at that time (Figure 3). This additional source could be either the AgNPs or the dissociation of Ag n clusters and complexes of Ag with hydrocarbons whose presence has been demonstrated in our earlier study (Bérard et al, 2021). The coinciding plateau in the intensity of the AgI line and the bump in the intensity of the ArI line can be associated with the moment when the AgNPs attach to the organosilicon NPs to form the core-satellite assemblies (raspberry-like NPs).…”

“…Although these studies are relatively recent and the achievements are not yet numerous, dust formation in reactive plasmas based on large chemical precursors has already been identified as promising for the development of thin nanocomposite films for microelectronic devices, sensor applications, healthcare applications, among others. In addition, it has recently been shown that the formation of dust nanoparticles in HMDSO-based plasmas appears to be of some interest for the study of stardust formation in laboratory experiments (Bérard et al, 2019;Bérard et al, 2021), as HMDSO contains key elements involved in stardust: carbon, oxygen, and silicon (Henning, 2010).…”

THE Formation of chondrule-like particles in RF discharge plasma

“…Currently, the investigation of the emergence and growth of dust particles in a 13,56 MHz radio-frequency (RF) discharge plasma, sustained in a mixture of argon and hexamthyldisiloxane (Ar-HMDSO) with HMDSO being the molecular precursor, is being carried out [24 -26]. Based on the formation of particles in a dusty plasma, the mechanisms of cosmic dust formation and the synthesis of its analogues in laboratory conditions are being investigated [27].…”

Isomer Differentiation of Trapped C16H10+ Using Low-Energy Collisions and Visible/VUV Photons

“…Molecular mass spectrometry analysis revealed that various carbonaceous samples contain a dominant peak at m / z = 202.078 corresponding to a polycyclic aromatic hydrocarbon (PAH) of formula C 16 H 10 . These samples include soot particles generated in flames, diesel fuels and particulate matter, cosmic dust analogues, , and carbonaceous chondrite meteorites. − Shukla and Koshi showed that in combustion reactions, different chemical pathways lead to the preferential formation of pyrene or fluoranthene. Each isomer could then lead to different species by subsequent growth.…”

“…The technique has been applied to soot samples. , Recent work in our group has demonstrated the very high sensitivity (attomole level) of the two-step LDI-MS in following molecular families of PAHs, carbon clusters, hydrogenated carbon clusters, and fullerenes. We have applied this technique to the analysis of laboratory analogues of stardust ,, and of meteorite samples. ,,, An originality of our setup is to be equipped with an ion trap so that ions can be activated by collisions or by absorption of photons and their dissociation features used to obtain information on the structure of the ions.…”