H 3+ : "A Beautiful Jewel of Nature"

Transcription

1 H 3+ : "A Beautiful Jewel of Nature" Ben McCall Department of Chemistry Department of Astronomy University of California at Berkeley [Oka Ion Factory ]

2 J. J. Thomson H + H 2 + H 3 + J. J. Thomson, Phil. Mag. 24, 209 (1912)

3 Arthur J. Dempster 10 mtorr 1.7 mtorr Discovered 235 U Physics Prof. at U. Chicago Principal American authority on positive rays H 3+ formed in secondary reaction A. J. Dempster, Phil. Mag. 31, 438 (1916)

4 Charles A. Coulson First Ph.D. student of Lennard-Jones First ab initio calculation on a polyatomic molecule "It appears that the ion H 3 + should exist in stable equilateral form with a nuclear distance about 0.85 Å, and that all excited levels are unstable." Prediction not accepted by Eyring, Hirschfelder, and others With advent of computers, prediction was confirmed (Christoffersen, Hagstrom, & Prosser 1964, Conroy 1964) C. A. Coulson, Proc. Camb. Phil. Soc. 31, 244 (1935)

5 Interstellar H 3 + Martin, McDaniel, & Meeks, Astrophys. J. 134, 1012 (1961)

6 Interstellar Chemistry E. Herbst & W. Klemperer, Astrophys. J. 185, 505 (1973) H 3+ universal protonator H 3+ + O H 2 + OH + also: W. D. Watson Astrophys. J. 183, L17 (1973) OH + + H 2 H + H 2 O + H 2 O + + H 2 H + H 3 O + H 3 O + + e - H 2 O + H Origin of Earth's water (?)

7 Herzberg's Search for H : with J. W. C. Johns, searched for emission in IR spectrum of discharge Looked for electronic transitions in VUV, found high rotational lines of Lyman bands Working in visible, stumbled onto H 3

8 Oka's Search for H 3 + Allen Karabonik

9 Positive Column Discharge Every morning, he transferred six 50 liter cans of liquid nitrogen to the laboratory!

10 The Long Search Four and a half years. Much of it assembling the DF system and discharge cell. Scanned from: 6/12-8/3 (1978) 12/18-1/26 ( ) 4/24-12/18 (1980) R(1,0) April 25, Oka and Allen Karabonik in lab Keiko came in at 10 pm Watson assigned it overnight

11 The final spectrum

12 A Beautiful Jewel of Nature T. Oka, Phys. Rev. Lett. 45, 531 (1980) T. Oka, "Laser Spectroscopy V," pp , 1981

13 The Search Was On Less than one year after first line was seen in laboratory!!!

14 Tom Geballe & IRTF

15 H 3+ on Jupiter! McDonald Observatory 2.7-m September 1987 November 1989 Study of H 2 Trafton, Lester, & Thompson, Astrophys. J. 343, L73 (1989) T. Oka, Rev. Mod. Phys. 64, 1141 (1992)

16 H 3+ Fundamental Band J'=1 J'=5 T. Oka and T. R. Geballe, Astrophys. J. 351, L53 (1990)

17 H 3+ as a Diagnostic J.E.P. Connerney and T. Satoh, Phil. Trans. R. Soc. Lond. A358, 2471 (2000) S. Miller, et al., Phil. Trans. R. Soc. Lond. A358, 2485 (2000)

18 Saturn and Uranus T. R. Geballe, M.-F. Jagod, & T. Oka, Astrophys. J. 408, L109 (1993) L. M. Trafton, et al., Astrophys. J. 405, 761 (1993)

19 Continued Laboratory Work 17 lab studies Chicago & Ottawa over 800 transitions Overtones 2ν 2 0 3ν 2 0 Hot bands 2ν 22 ν 2 2ν 20 ν 2 Combination bands ν 1 + 2ν ν 1 + ν 2 0 Forbidden bands ν 1 0 ν 1 + ν 2 ν 2

20 Compilation Work Reassignment of all observed transitions Experimentally determined energy levels utilize variety of band types observed independent of theory 526 energy levels Test for theory Reliable linelist C. M. Lindsay & B. J. McCall, J. Mol. Spectrosc. 210, 60 (2001)

21 H 3+ Above the Linearity Barrier J. L. Gottfried, B. J. McCall, & T. Oka, J. Chem. Phys. 118, (2003) poster: Jennifer Gottfried

22 Back to the Interstellar Search CSHELL on IRTF CGS4 on UKIRT Infrared array detectors

23 T. R. Geballe & T. Oka, Nature 384, 334 (1996) First detection!

24 Confirmed by Doppler Shift April July April AFGL2136 reprocessed Doppler shift confirms interstellar origin July W33A B. J. McCall, T. R. Geballe, K. H. Hinkle & T. Oka, Astrophys. J. 522, 338 (1999)

25 H 3+ as a Probe of Dense Clouds Spectrum gives N(H 3+ ) = cm -2 Given n(h 3+ ) from model, and N(H 3+ ) from infrared observations: path length L = N/n ~ cm ~ 1 pc density n(h 2 ) = N(H 2 )/L ~ cm -3 temperature T ~ 30 K 1.02 AFGL 2136 Unique probe of clouds Consistent with expectations AFGL 2591 confirms dense cloud chemistry B. J. McCall, T. R. Geballe, K. H. Hinkle & T. Oka, Astrophys. J. 522, 338 (1999)

26 The Galactic Center N para = 5.1(1.7) cm -2 N ortho = 2.4(1.1) cm -2 N broad = 17.5(3.9) cm -2 T. R. Geballe, B. J. McCall, K. H. Hinkle & T. Oka, Astrophys. J. 510, 251 (1999)

27 Cygnus OB2 12 N para = 2.4(3) cm -2 N ortho = 1.4(2) cm -2 Similar column density to dense clouds!! observed at UKIRT observed at Kitt Peak B. J. McCall, T. R. Geballe, K. H. Hinkle & T. Oka, Science 279, 1910 (1998)

28 Formation Chemistry & Implications cosmic ray H 2 H 2+ + e - H 2 + H 2+ H 3+ + H (fast) Rate = ζ [H 2 ] Destruction H 3+ + e - H + H 2 or 3H Steady State path length L = N/n ~ 1 kpc density n(h) = N(H)/L ~ 20 cm -3 = Rate = k [H 3+ ] [e - ] = ( s -1 ) ( cm 3 s -1 ) (2400) = 10-7 cm -3 Density Independent!

29 Other Diffuse Clouds, too! General problem with chemical model: HD ζ k e [e - ]/[H 2 ] McCall, et al. Astrophys. J. 567, 391 (2002)

30 H 3+ toward ζ Persei Rules out [e - ]/[H 2 ] N(H 2 ) from Copernicus N(C + ) from HST ζ Persei Savage et al. Astrophys. J. 216, 291 (1977) Cardelli et al. Astrophys. J. 467, 334 (1996)

31 H 3+ Dissociative Recombination Laboratory values of k e varied by 4 orders of magnitude! Even worse: theory in infancy, way off... Big problem: not measuring H 3+ in ground states k e (30K) year

32 Storage Ring Measurements CRYRING 20 ns electron beam H ns H, H 2 + Complete vibrational relaxation + Very simple experiment + Control H 3+ e - impact energy - Rotationally hot ions produced - No rotational cooling in ring

33 Berkeley Supersonic Ion Source Supersonic expansion leads to rapid cooling Discharge from ring electrode downstream Skimmer to minimize arcing Gas inlet 2 atm H 2 Solenoid valve Pinhole flange/ground electrode Insulating spacer -900 V ring electrode Skimmer H 3 +

34 CRYRING Results Rules out k e Considerable amount of structure (resonances) in the cross-section k e = cm 3 s -1 McCall, et al. Nature 422, 500 (2003)

35 Implications for ζ Persei N(H 3+ ) L = [H 3+ ] = ζ N(H 2 ) k e N(e - ) ζ L = k e N(H 3+ ) ζ L = 8000 cm s -1 N(e - ) ( cm 3 s -1 ) ( cm -2 ) ( ) N(H 2 ) Adopt ζ= s -1 Adopt L=2.1 pc L = 85 pc ζ= s -1 n = 6 cm -3 (40x higher!)

36 Extrasolar Planetary H 3+? S. D. Brittain & T. W. Rettig, Nature 418, 57 (2002)

37 T. Oka, Physics Today July 1997