A New 3.25 Micron Absorption Feature toward Monoceros R2/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.