  The current assignments of the 11.3 feature are shown to be incompatible with
observations. An unbiased survey of correlation charts suggests that the
olefinic group R2=CH2 is a good alternative candidate. For the 12.7 feature,
the best fits are provided by nitrites, R-O-N=O, and amines, R-N=H2. Sulfones,
SO2, exhibit strong features near 7.7 and 8.6 microns, which may contribute to
the UIBs. These additional functional groups are likely to be attached to the
main hydrocarbon dust skeleton previously hypothesized in the coal/kerogen
model. They provide further leeway in modelling the large variety of relative
band intensities observed in the sky.
