Mechanochemical synthesis of Aromatic Infrared Band carriers. The top-down chemistry of interstellar carbonaceous dust grain analogues

Abstract

Interstellar space hosts nanometre- to micron-sized dust grains. The carbonaceous-rich component of these grain populations emits in infrared bands, observed remotely for decades with telescopes and satellites. They are a key ingredient of astrochemical dust evolution. The precise carriers for most of these bands are still unknown and not well reproduced in the laboratory. In this work, we show the high-energy mechanochemical synthesis of disordered aromatic and aliphatic analogues provides interstellar relevant dust particles. The mechanochemical milling of carbon-based solids under a hydrogen atmosphere produces particles with a spectroscopic match to astrophysical observations of aromatic infrared band (AIB) emission. The H/C ratio for the analogues that best reproduce these astronomical infrared observations lies in the 5$\pm$2% range. This value is much lower than diffuse interstellar hydrogenated amorphous carbons, another Galactic dust grain component observed in absorption, and it most probably provides a constraint on the hydrogenation degree of the most aromatic carbonaceous dust grain carriers. A broad band, observed in AIBs, in the 7.4-8.3 $\mu$m range is correlated to the hydrogen content, and thus the structural evolution in the analogues produced. The mechanochemical process can be seen as an experimental reactor to stimulate local energetic chemical reactions. It introduces bond disorder and hydrogen chemical attachment on the produced defects, with an effect similar to the interstellar space very localised chemical reactions with solids. From the vantage point of astrophysics, these laboratory interstellar dust analogues will be used to predict dust grain evolution under simulated interstellar conditions, including harsh radiative environments. Such interstellar analogues offer an opportunity to derive a global view on the cycling of matter in other star forming systems.

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Cited by in corpus (6)

• PDRs4All IV. An embarrassment of riches: Aromatic infrared bands in the Orion Bar
• PDRs4All: A JWST Early Release Science Program on radiative feedback from massive stars
• The Role of Terahertz and Far-IR Spectroscopy in Understanding the Formation and Evolution of Interstellar Prebiotic Molecules
• Characterization of interstellar carbon dust analogues synthesized by dielectric barrier discharge and evolution after irradiation with 3 MeV H+
• Polycyclic aromatic hydrocarbon (PAH) abundances in the disk around T Chamaeleontis (T Cha): PAH sizes, ionization fraction, and mass during JWST observations
• Interstellar Hydrocarbons: Degradation Chemistry in Diffuse Clouds