dN/dt/n_H at T = 10⁵ K and at T = 10⁷ K. Red line: rate constant for a-C:H grains. Black lines: rate constant for PAHs; the dotted line shows nuclear interaction only, the dashed line the summed effects of nuclear and electronic interactions, whilst the solid line includes electron collisions as well. The results for T = 10⁶ K are not shown here but are very similar to those for T = 10⁷ K.