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DAVID C. KNAUTH, Department of Physics and Astronomy, Northwestern University, Evanston, IL 60208; B-G ANDERSSON, S. R. MCCANDLISS, H. W. MOOS, Department of Physics and Astronomy, The Johns Hopkins University, Baltimore, MD 21218.

Molecular nitrogen (N₂) is the most abundant molecule in the Earth's atmosphere and in the less chemically-processed atmosphere of Titan. N₂ is also of considerable interest for studies of the interstellar medium because both models of steady-state gas-phase chemistry (Viala 1986) and millimeter wave observations of N₂H⁺ (Womack, Ziurys, & Wyckoff 1992) predict that N₂ should be the dominant nitrogen-bearing molecule in interstellar space. We previously presented the first detection of interstellar N₂ toward HD~124314 with an observed fractional abundance of N₂/H₂ = x(N₂) = 3.3 × 10^-7 (Knauth et al. 2004). Here we report on the second detection of interstellar N₂ based on Far Ultraviolet Spectroscopic Explorer (FUSE) observations of the moderately-reddened star 20 Aquilae (Knauth et al. 2005) with x(N₂) 4.7 × 10^-8. This fractional abundance is surprisingly low given that 20 Aql has a factor-of-4 higher CN abundance than that found toward HD~124314. Is this possible anti-correlation caused by differences in the predictions of diffuse and dark cloud chemistry? Recent work (Herbst 2004, private communication; Roueff 2005) show that a single homogeneous cloud chemical model cannot reproduce the observations. Further observations of interstellar N₂ and other nitrogen-bearing species (e.g., NH) toward lines of sight with different physical conditions are required to understand the implications for interstellar nitrogen chemistry.