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Adventures with H 3 +

Adventures with H 3 +. Tom Geballe (Gemini Observatory) with thanks to: Takeshi Oka (U. Chicago) Ben McCall (U. Illinois), Miwa Goto (ESO- Garching ), Nick Indriolo (U. Michigan), Tomonori Usuda (Subaru Telescope) and the staffs of the

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Adventures with H 3 +

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  1. Adventures with H3+ Tom Geballe (Gemini Observatory) with thanks to: Takeshi Oka (U. Chicago) Ben McCall (U. Illinois), Miwa Goto (ESO-Garching), Nick Indriolo (U. Michigan), Tomonori Usuda (Subaru Telescope) and the staffs of the United Kingdom Infrared Telescope (UKIRT), Gemini, Subaru, and the Very Large Telescope (VLT)

  2. The molecule at the starting point of gas phase interstellar chemistryanda unique probe of conditions in interstellar clouds H2 H 1p, 1e 2p, 2e 3p, 2e H3+

  3. Discovery of H3+ in 1911 J.J. Thomson (Cambridge) – discoverer of the electron; inventor of the mass spectrometer “On several plates taken when the discharge tube contains hydrogen, the existence of a primary line for which m/e=3 has been detected. There can be little doubt that this line is due to H3 … the existence of this substance is interesting from a chemical point of view, as it is not possible to reconcile its existence with the ordinary conceptions about valency, if hydrogen is regarded as always monovalent.” - Thomson, Phil Mag., 24, 209 (1912) H3+ ions follow paths of constant charge/mass Thomson’s discovery photograph

  4. H3+ can be abundant in pure hydrogen discharges •  H3+is stable • (dissociation energy ~4 eV, same as H2) • Produced by the ion-molecule reaction • H2+ + H2 H3+ + H + ΔE • Hogness & Lumm (1925) • The same reaction produces H3+ in interstellar gas. • But what ionizes H2in interstellar gas? Dempster 1916) H3+ H2+ H+ supernova Answer Accreting massive black hole

  5. Why is H3+ important? Follow the sequence of reactions (bottom to top) H2 + CR  H2+ + e- ζ = 3 x 10-17 sec-1(~109 yr) (but 1040 H2 molecules per sec are ionized in a 1M cloud !) … H2+ + H2 H3+ + H … H3+ + X HX+ + H2 (X ≠ He, N, O2) … .. HX+ + Y XY+ + H (Y often H2) … H3+ is the starting point of gas phase chemistry. Tree of interstellar gas phase chemistry in dense (n>103 cm-3) clouds Watson (1973); Herbst & Klemperer (1973)

  6. Takeshi Oka (measured IR spectrum of H3+ in the lab in 1980)

  7. Oka JAPAN, 1956

  8. UKIRT, July 15, 1996: two lines of H3+ detected in dense interstellar clouds H3+ bright star bright star Dense cloud (optical) Measured amounts of H3 consistent with ion-molecule chemistry models

  9. Huge amount of H3+ toward the Galactic center H3+ doublet UKIRT July 11 1997 GC IRS 3 AV = 30 mag GALACTIC CENTER SPECTRA GCS 3-2 (30 pc from IRS3) AV = 30 mag GL 2136 AV = 60 mag MOLECULAR CLOUD SPECTRUM • ~30X more H3+ toward GC than in typical Galactic dense clouds • Only half as much gas toward GC as toward GL2136 Needless to say, we were puzzled.

  10. Later that same night … Surprisingly large amounts of H3+ in diffuse clouds Dense cloud Cygnus OB2 No. 12 diffuse cloud July 11, 1997 Dense cloud 6X less gas and much higher ne than dense cloud, but same N(H3+) !

  11. JULY11, 1997: TWO PUZZLES Why is there so much H3+ in diffuse clouds ? Even if H3+ is much more abundant in diffuse clouds than we had thought, how could there be such a vast amount of H3+ toward and/or in the Galactic center ? Spitzer+VLA (Far-IR + Radio) view of the Galactic center

  12. 1. Why is there so much H3+ in diffuse clouds ? There is a large population of low energy cosmic rays that penetrates diffuse clouds and ionizes H2, but does not penetrate dense clouds. So ionization rate of H2 is 10X higher in diffuse clouds.

  13. Some of H3+ is in gas in foreground spiral arms. (produces narrow absorption features) Lots of H3+ is in warm and diffuse gas within the GC (previously thought to take up an insignificant fraction of volume there). 4.5 kpc arm Local arm 3 Kpc arm Galactic Center • 2. Why is there such • a vast amount of H3+ • in the Galactic center ? • Previously unsuspected large volume of warm diffuse gas • (b) higher density of cosmic rays • in the GC produces more H3+ • than in diffuse clouds elsewhere Warm, diffuse, in GC local 4.5 kpc 3 kpc

  14. H3+ in SATURN (disc 1993) H3+ in JUPITER (disc. 1988) H3+ H3+ H3+ H3+ H3+ lines in URANUS (disc. 1993) H3+ IN THE SOLAR SYSTEM

  15. FUTURE SCIENCE WITH H3+ Jupiter Some could have extremely bright H3+ line emission. (1) Exo-planet “Jupiters” much closer to their suns HISTORY OF THE UNIVERSE (2) The first Stars The early universe contained only H and He. Radiation by H3+ probably was an important coolant allowing the gravitational collapse of clouds into the first generation of stars. Research involving H3+ will continue to contribute to our understanding of the universe.

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