A New 3 . 25 Micron Absorption Feature toward Mon R 2 / IRS - 3

A new 3.2–3.5 µm spectrum of the protostar Mon R2/IRS-3 confirms our previous tentative detection of a new absorption feature near 3.25 µm. The feature in our new spectrum has a central wavelength of 3.256 µm (3071 cm −1) and has a full-width at half maximum of 0.079 µm (75 cm −1). We explore a possible identification with aromatic hydrocarbons at low temperatures, which absorb at a similar wavelength. If the feature is due to aromatics, the derived column density of C–H bonds is ∼1.8 × 10 18 cm −2. If the absorbing aromatic molecules are of roughly the same size as those responsible for aromatic emission features in the interstellar medium, then we estimate that ∼9% of the cosmic abundance of carbon along this line of sight would be in aromatic hydrocarbons, in agreement with abundance estimates from emission features.