The 6 $\mu$m Feature as A Tracer of Aliphatic Components of Interstellar Carbonaceous Grains

TL;DR

This paper proposes that the 6 μm infrared emission feature in interstellar sources originates from olefinic double-bond groups attached to aromatic carbonaceous grains, offering a new perspective on the composition of interstellar dust.

Contribution

It introduces the idea that the 6 μm UIE feature is due to olefinic groups, challenging previous attributions to C=O modes, and links this to hydrogenation processes.

Findings

The 6 μm feature is likely from olefinic groups attached to aromatic rings.

Olefinic groups may form through hydrogenation of aromatic structures.

This interpretation provides insights into the chemical composition of interstellar dust.

Abstract

An unidentified infrared emission (UIE) feature at 6.0 $\mu$m is detected in a number of astronomical sources showing the UIE bands. In contrast to the previous suggestion that this band is due to C=O vibrational modes, we suggest that the 6.0 $\mu$m feature arises from olefinic double-bond functional groups. These groups are likely to be attached to aromatic rings which are responsible for the major UIE bands. The possibility that the formation of these functional groups is related to the hydrogenation process is discussed.