1. Galactic Center Region Concentrated stars and interstellar matter High Energy Density (gravity, MHD, kinetic) Strong magnetic field :B ~ mG High external pressure:P/k  5 x 10 6 cm –3 K Center ~ 500 pc

2. Harry Kroto Some spectroscopic issues in astrophysical chemistry Oka Introductory remark Jacek Krelowski Absorption spectra of dark interstellar clouds John Maier Gas phase laboratory studies of electron spectra of carbon containing molecules of relevance to astrophysics Wolfgand Krätschmer Carbon clusters as interstellar molecules and grains

3. Astronomers’ Periodic Table Ben McCall H He CN O Ne SiS Ar Mg Fe

4. Metastable H 3 + near the Galactic center: Interplay between radiative and collisional interactions Thomas R. Geballe Gemini Observatory Miwa Goto Max-Planck-Institut für Astronomie Tomonori Usuda Subaru Telescope Benjamin J. McCall University of Illinois, Urbana-Champaign Interstellar Reactions, Dresden, June 6, 2005 Takeshi Oka Department of Chemistry and Department of Astronomy and Astrophysics The Enrico Fermi Institute, The University of Chicago

5. 1975 H–C≡C–C≡C–C≡N H–C≡C–C≡C–C≡C–C≡N H–C≡C–C≡C–C≡C–C≡C–C≡N C 60 H3+H3+

6. 2005 Hot and Diffuse Clouds near GC Probed by Metastable H 3 + Oka, Geballe, Goto, Usuda, McCall 1998 – 2002 Ubiquity, Dense and Diffuse Clouds McCall, Geballe, Hinkle, Oka Historical Sketch of H 3 + Observation + 1951 1970 1996 1980 Oka, PRL. 45, 531 Laboratory Spectrum1996 Geballe, Oka, Nature 384, 334 Interstellar H 3 +, Discovery H H2H2 H3+H3+ 1989 - 95 2002 Metastable H 3 +, Discovery Goto, McCall, Geballe, Oka, et al. 1975

7. Three Proton System I = 3/2 ortho g I = 4 I = 1/2 para g I = 2 + J K 32.9 K 361 K (J, K)

8. Symmetry Breaking : forbidden Δk = ± 3 transitions Interstellar NH 3 Oka, Shimizu, Shimizu, Watson, ApJ 165, L15 (1971) Interstellar H 3 + Pan, Oka, ApJ 305, 518 (1986) μ Critical Density 200 cm -3 K Collision H 3 + + H 2 → (H 5 + ) * → H 3 + + H 2 J (J, K) K 27.2 days (3,3) metastable (2,2) unstable (1,1) ground (1,0)

9. The Central Molecular Zone M ~ 5 × 10 7 M ⊙ Dominantly molecular n(H 2 ) > 10 4 cm -4 Volume filling factor 0.1 Hot gas T ~ 300 K High velocity dispersion Low dust temperature Mezger, Duschl, Zylka, A&A Rev. (1996) Morris, Serabyn, ARA&A (1996)

10. Telescopes and Spectrometers UKIRT 3.8 m CGS4 8 km s -1 Mauna Kea Subaru 8 m IRCS 15 km s -1 Mauna Kea Gemini South 8 m Phoenix 5 km s -1 Cerro Pachon

11. Galactic plane Quintuplet

12. Yusef-Zadeh, Morris, AJ, 94, 1178 (1987)

13. The Quintuplet Okuda et al. ApJ 351, 89 (1990)

14. Discovery of metastable H 3 + Goto, McCall, Geballe, Usuda, Kobayashi, Terada, Oka PASJ, 54, 951 (2002)

16. (1,1) ground (3,3) metastable (2,2) unstable CO

17. The Expanding Molecular Ring Kaifu, Kato, Iguchi, Nature (1972) Scoville, ApJ (1972) Whiteoak, Gardner, MNRAS (1979)

18. (1, 1) ground level CMZ and spiral arms (3, 3) metastable level All CMZ (2, 2) unstable level Neither CO All spiral arms High temperature Low density -100 km/s 0 km/s -50 km/s

19. Radiation Collision Reaction Rigorous Selection Rules Approximate Rules Random +  - ΔJ = ± 1, 0 ortho  para ΔI = 0 ortho  para ΔI = 0 ΔI total = 0 AAAA BBBB CACA DBDB Ψ’ψΨ’ψ T rad  3 K « T kin

20. Rate Equations Production Spontaneous emission 4  10 -7 s -1 Collision n(H 2 ) 100 cm -3 10 -7 s -1 Destruction 10 -9 s -1 10 -17 s -1 10 -7 cm 3 s -1 10 -9 cm 3 s -1 H 3 + + H 2  (H 5 + )*  H 3 + + H 2 Detailed balance Cosmic ray ionization Dissociative recombination Proton hop reaction 0 = Steady State Oka, Epp ApJ, 613, 349 (2004)

21. Discovery of high temperature (T ~ 250 K), low density (n ≤ 100 cm -3 ) clouds Oka & Epp, ApJ 613,349 (2004)

23. Main Results so far Vast amount of gas High temperature: T ~ 250 K Low Density: n ~ 100 cm -3 H 3 + total column density: 4.3  10 15 cm -2 ¾ in CMZ, ¼ in intervening spiral arms ½ of H 3 + in CMZ in the Expanding Mol. Ring Pathlength ~ 50 pc Ionization rate ~ 5  10 -15 s -1

24. Hot and Diffuse Gas, Questions abound What is the heating mechanism? How is the pressure balanced? How are they related to molecular clouds and H II regions? What is the relation to X-ray (  -ray) sources? What is their role in the strong magnetohydrodynamic effects?

25. Galactic plane Quintuplet

26. Gemini South