  Polycyclic aromatic hydrocarbon (PAH) molecules are widely considered as the
preferred candidate for the carrier of the unidentified infrared emission bands
observed in the interstellar medium and circumstellar envelopes. In this paper
we report the result of fitting a variety of non-PAH spectra (silicates,
hydrogenated amorphous carbon, coal and even artificial spectra) using the
theoretical infrared spectra of PAHs from the NASA Ames PAH IR Spectroscopic
Database. We show that these non-PAH spectra can be well fitted by PAH
mixtures. This suggest that a general match between astronomical spectra and
those of PAH mixtures does not necessarily provide definitive support for the
PAH hypothesis.
