EXCITATION OF THE AROMATIC INFRARED EMISSION BANDS: CHEMICAL ENERGY IN HYDROGENATED AMORPHOUS CARBON PARTICLES?

We outline a model for the heating of hydrogenated amorphous carbon (HAC) dust via the release of stored chemical energy and show that this energy (similar to 12 kJ mole(-1)) is sufficient to heat dust grains of classical size (50-1000 angstrom) 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 similar to 50 atoms can produce emission at 3.3 mu m.