2004ApJ...604..252P

We report infrared spectral evidence of deuterated interstellar polycyclic aromatic hydrocarbons (PAHs). Two bands are detected in the infrared emission from the ionization bar in Orion at 4.4 and 4.65 µm. The one at 4.65 µm is present at the 4.4 σ level, while the one at 4.4 µm is more tentative, with a σ equal to 1.9. An emission band at 4.65 µm is also detected in the infrared emission from M17 by Verstraete and coworkers at the 4.4 σ level. These wavelengths are highly characteristic of CD stretching modes of deuterated PAHs and fall in a featureless region of the interstellar spectrum. The IR spectroscopic properties of deuterated PAHs are summarized, and an estimate of the deuterium fractionation between the aromatic and aliphatic carbons associated with the PAHs is given. High deuterium fractionation is implied; this is discussed in terms of interstellar PAH fractionation mechanisms.