Contribution of polycyclic aromatic hydrocarbon molecules to the interstellar extinction curve

Absorption cross sections of terrestrial mixtures of gaseous polycyclic aromatic hydrocarbons (PAHs) have been measured in the visible to far-UV range. The spectral signatures obtained are compatible with those of the extinction curve. These results support the PAH model which attributes the 'unidentified' IR emission bands to these molecules. Interstellar PAHs can give an important contribution to the 2175 A bump, and do absorb in the far-UV rise. They are inferred to contain about 18 percent of the cosmic carbon.