Excitation of the aromatic infrared emission bands: Chemical energy in hydrogenated amorphous carbon particles?

TL;DR

This paper proposes a model where chemical energy stored in hydrogenated amorphous carbon dust heats grains sufficiently to produce aromatic infrared emission bands, offering an alternative excitation mechanism to stochastic heating.

Contribution

It introduces a chemical energy release mechanism in HAC dust as a new source for exciting aromatic infrared emission bands, expanding understanding beyond stochastic heating models.

Findings

Chemical energy (~12 kJ/mole) can heat dust grains to emit IR bands.

Heating is consistent with dangling bond concentrations and H atom recombination.

Chemical energy release can supplement or replace stochastic heating for IR emission.

Abstract

We outline a model for the heating of hydrogenated amorphous (HAC) dust via the release of stored chemical energy and show that this energy (~12 kJ/mole) is sufficient to heat dust grains of classical size (50-1000 {\AA}) to temperatures at which they can emit at 3.3 {\mu}m and other "UIR" wavelengths. Using laboratory data, we show that this heating process is consistent with a concentration of a few percent of dangling bonds in HAC and may be initiated by the recombination of trapped H atoms. We suggest that the release of chemical energy from dust represents an additional source of excitation for the UIR bands relaxing the previous requirement that only stochastically heated molecules having fewer than ~ 50 atoms can produce emission at 3.3 {\mu}m.