Unidentified Infrared Emission bands: PAHs or MAONs?

TL;DR

This paper proposes that the unidentified infrared emission bands are caused by amorphous carbonaceous solids with mixed aromatic and aliphatic structures, challenging the previous PAH molecule hypothesis.

Contribution

It introduces the idea that UIE carriers are amorphous solids with mixed structures, supported by spectral fitting showing significant aliphatic emission.

Findings

Aliphatic components emit a significant portion of the energy.

Spectral fits favor amorphous solid structures over free-flying PAH molecules.

Arguments support a solid-state carrier rather than a gas-phase molecule.

Abstract

We suggest that the carrier of the unidentified infrared emission (UIE) bands is an amorphous carbonaceous solid with mixed aromatic/aliphatic structures, rather than free-flying polycyclic aromatic hydrocarbon (PAH) molecules. Through spectral fittings of the astronomical spectra of the UIE bands, we show that a significant amount of the energy is emitted by the aliphatic component, implying that aliphatic groups are an essential part of the chemical structure. Arguments in favor of an amorphous, solid-state structure rather than a gas-phase molecule as a carrier of the UIE are also presented.