Release of large polycyclic aromatic hydrocarbons and fullerenes by cosmic rays from interstellar dust

T Pino,A Wucher,C Trautmann,K Béroff,M Bender,M Godard,K C Le,L Breuer,M Herder,E Dartois,M Chabot,F Fernandez-Villoria,D Severin

doi:10.1051/0004-6361/201834855

Abstract

Context. Top-down chemistry is believed to be responsible for the formation of the large molecular compounds such as the polycyclic aromatic hydrocarbon-like molecules and the fullerenes observed in the interstellar medium. The release of these large molecules from the parent grains remains an important issue to be investigated. Aims. Cosmic rays irradiate the dust grains during their journey in the interstellar medium. In this study we probe to what extent electronic sputtering and/or desorption processes induced by high-energy ion projectiles contribute to the creation of the large molecular component in space. Methods. Carbonaceous dust analogues were produced in an ethylene flame. The resulting soot nanoparticles generated under well-defined conditions were irradiated by swift heavy ions, and mass spectra of the ionic and neutral molecular fragments emitted shortly after the impact were monitored. Results. Large molecular fragments were detected, including neutral and ionic polycyclic aromatic hydrocarbons containing up to several tens of carbon atoms, as well as ionic fullerenes. Although the absolute efficiencies were not obtained, these experiments provide a proof of principle of a top-down scenario involving interaction processes of interstellar dust with high-energy projectiles yielding large molecular compounds observed in space.

Highlights

It is strongly suspected that large carbonaceous molecules carry the aromatic infrared bands (AIBs) observed in many lines of sight throughout the interstellar medium (ISM)
The position of the bands and the emission mechanism led to the so-called polycyclic aromatic hydrocarbon (PAH) hypothesis and the presence of a molecular component in the form of polycyclic aromatic aliphatic mixed hydrocarbons is well accepted (Sloan 2017; Jones et al 2017; Yang et al 2017; Pilleri et al 2015; Sloan et al 2014, 2007; Carpentier et al 2012; Acke et al 2010; Pino et al 2008)
Concluding remarks Emitted molecular fragments from a laboratory analogue of carbonaceous interstellar dust irradiated by swift heavy ion simulating cosmic ray effects were measured

Summary

Introduction

It is strongly suspected that large carbonaceous molecules carry the aromatic infrared bands (AIBs) observed in many lines of sight throughout the interstellar medium (ISM). The position of the bands and the emission mechanism led to the so-called polycyclic aromatic hydrocarbon (PAH) hypothesis and the presence of a molecular component in the form of polycyclic aromatic aliphatic mixed hydrocarbons is well accepted (Sloan 2017; Jones et al.2017; Yang et al 2017; Pilleri et al 2015; Sloan et al 2014, 2007; Carpentier et al 2012; Acke et al 2010; Pino et al 2008) The size of these large molecules ranges from a few tens to a few hundred atoms. The most recent assignment of five diffuse interstellar bands, observed in absorption in the near-infrared, to the vibronic bands of the first eetleaclt.ro2n0i1c5t)radnesfiitniiotnelyinpCro+6v0e(dCathmapt bthelel et al ISM

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