Analogs of solid nanoparticles as precursors of aromatic hydrocarbons

¹ Astrophysical Institute and University Observatory, Friedrich Schiller University, Schillergässchen 2/3, 07745 Jena, Germany
e-mail: Kamel.Gadallah71@gmail.com
² Astronomy Dpt., Faculty of Science, Al-Azhar University, Nasr City, PO Box 11884 Cairo, Egypt
³ Institute of Solid State Physics, Friedrich Schiller University of Jena, Helmholtzweg 3, 07743 Jena, Germany

Received: 12 December 2012
Accepted: 20 April 2013

Abstract

Context. Aromatic =CH and C=C vibrational bands have been observed within shocked interstellar regions, indicating the presence of aromatic emission carriers such as PAHs, which may have been created from adjacent molecular cloud material by interaction with a shock front.

Aims. We investigate the evolution of the aromatic =CH and C=C vibrational modes at 3.3 and 6.2 μm wavelength in heated HAC materials, PAHs and mixed PAHs and HACs, respectively, aiming at an explanation of the evolution of carbonaceous dust grains in the shocked regions.

Methods. Materials used in these analogs (HAC and PAH materials) were prepared by the laser ablation and the laser pyrolysis methods, respectively. The transmission electron microscopy (TEM) in high-resolution mode was used as an analytical technique to characterize the aromatic layers in HACs. Spectroscopic analysis was prformed in the mid-IR range.

Results. A remarkable destruction of aliphatic structures in HACs has been observed with the thermal processing, while aromatic structures become dominating by increasing the diameters of the graphene layers. The aromatic bands at 3.3 and 6.2 μm, observed in the laboratory spectra of PAHs and of the combination of the PAHs and HAC materials, are also clearly observed in the spectrum of the heated HACs. These bands agree with those of aromatic bands observed in astronomical observations.

Conclusions. Aromatization of HACs could be a pre-stage in the decomposition process of hydrocarbons that form PAH-clusters in such hot interstellar medium.