  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.
