1. Interstellar N 2 toward 20 Aql

2. Observations of the Interstellar Medium

3. Why N 2 ? N 2, the most abundant molecule in the Earth's and Titan’s atmospheres. Studies of interstellar N 2 H + in dark molecular clouds (Womack, Ziurys & Wyckoff 1992) predict N 2 is the most abundant nitrogen-bearing molecule. Using Copernicus, Lutz, Snow, & Owen (1979) reported upper limits N 2 < 5 x 10 12 cm -2 toward  Sco and  Per. N 2, the most abundant molecule in the Earth's and Titan’s atmospheres. Studies of interstellar N 2 H + in dark molecular clouds (Womack, Ziurys & Wyckoff 1992) predict N 2 is the most abundant nitrogen-bearing molecule. Using Copernicus, Lutz, Snow, & Owen (1979) reported upper limits N 2 < 5 x 10 12 cm -2 toward  Sco and  Per.

4. Why hasn’t anyone found N 2 before? N 2 is an homonuclear molecule, like H 2 its electronic ground state transitions are only observable in the far ultraviolet below 1100 Å. Only a few satellite missions covered this wavelength range. FUSE has superb data quality. N 2 is an homonuclear molecule, like H 2 its electronic ground state transitions are only observable in the far ultraviolet below 1100 Å. Only a few satellite missions covered this wavelength range. FUSE has superb data quality.

5. FUSE - the little satellite that could!

6. N 2 toward 20 Aql

7. N 2 Models Synthetic N 2 profiles, assuming level populations for the c´ 4 band at 958 Å (shown) and c 3 band at 960 Å. N 2 is sensitive to the temperature of the gas. Synthetic N 2 profiles, assuming level populations for the c´ 4 band at 958 Å (shown) and c 3 band at 960 Å. N 2 is sensitive to the temperature of the gas.

8. 20 AqlHD 124314 N(N 2 ) (cm -2 )(3.2 ± 0.7) x 10 13 (4.6 ± 0.8) x 10 13 N(CN) (cm -2 )(4.2 ± 0.1) x 10 12 (6.4 ± 2.2) x 10 11 N(N 2 )/N(H 2 )4.7 x 10 -8 3.3 x 10 -7 N(CN)/N(N 2 )0.1250.014 T (K)7040 n (cm -3 )11001000

10. Discussion  Interstellar NH in diffuse clouds (Meyer & Roth 1991) is more than an order of magnitude larger than expected. Interstellar H 3 + are more than an order of magnitude larger than expected in diffuse clouds (McCall et al. 2003).  Recent observations of NH 3 toward  Oph A (Liseau et al. 2003) show that NH 3 is under abundant.  Geppert et al. (2004) suggest that NH formation is the preferred route over N 2.  Interstellar NH in diffuse clouds (Meyer & Roth 1991) is more than an order of magnitude larger than expected. Interstellar H 3 + are more than an order of magnitude larger than expected in diffuse clouds (McCall et al. 2003).  Recent observations of NH 3 toward  Oph A (Liseau et al. 2003) show that NH 3 is under abundant.  Geppert et al. (2004) suggest that NH formation is the preferred route over N 2.

11. Evolution of the ISM How does the ISM transition between phases? Further observations of interstellar N 2 may help us understand the transition between diffuse and molecular clouds. How does the ISM transition between phases? Further observations of interstellar N 2 may help us understand the transition between diffuse and molecular clouds.

12. Conclusions We present the 2 nd detection of interstellar N 2. Measurements of N 2 H + in dark clouds are in agreement with our findings. Results on N 2, NH, and H 3 + suggests that interstellar nitrogen chemistry needs to be modified. May require new production mechanism, changes in reaction rates and/or inclusion of grain surface reactions. We present the 2 nd detection of interstellar N 2. Measurements of N 2 H + in dark clouds are in agreement with our findings. Results on N 2, NH, and H 3 + suggests that interstellar nitrogen chemistry needs to be modified. May require new production mechanism, changes in reaction rates and/or inclusion of grain surface reactions.

13. What Now? We have pending FUSE observations of N 2. To address interstellar nitrogen chemistry, knowledge of CN, NH, NO, N 2 H +, NH 2 +, H 3 +, HCO + are needed. We have pending FUSE observations of N 2. To address interstellar nitrogen chemistry, knowledge of CN, NH, NO, N 2 H +, NH 2 +, H 3 +, HCO + are needed.

14. CN and NH toward HD 124314

15. CN and preliminary NH toward 20 Aql

16. Acknowledgements B-G Andersson H. W. Moos S. R. McCandliss J. T. Lauroesch Dave M. Meyer Gerry Williger FUSE Mission Planners B-G Andersson H. W. Moos S. R. McCandliss J. T. Lauroesch Dave M. Meyer Gerry Williger FUSE Mission Planners