Storage Ring Measurements of the DR Rate of Rotationally Cold H

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1 Storag Ring Masurmnts of th DR Rat of Rotationally Cold H 3 Bn McCall Dpartmnt of Chmistry Dpartmnt of Astronomy Univrsity of llinois at Urbana-Champaign A. J. Hunycutt, R. J. Saykally (Univrsity of California at Brkly) N. Djuric, G. H. Dunn (Univrsity of Colorado & NIST) J. Smaniak, O. Novotny (Świtokrzyska Acadmy, Poland) A. Paal, F. Östrdahl (Mann Sigbahn Laboratory) A. Al-Khalili, A. Ehlrding, F. Hllbrg, S. Kalhori, A. Nau, R. Thomas, M. Larsson (Stockholm Univrsity)

2 Why Am I Hr? Thy ll nvr gt cold nough ions with a liquid nitrogn coold sourc! Why don t thy just us a suprsonic xpansion sourc? I m a molcular spctroscopist I m also an astronomr Thsis work on H3 (Oka group) Study H3 in diffus clouds DR is important

3 Astronomr's Priodic Tabl H C N O N Mg Si S Ar F

4 Tr of Intrstllar Chmistry C m H n HO 2 OH HCO 2 CHOH 2 5 CH OCH 3 3 CH OH 3 CH CO 2 HO 3 CH OH H 2 CO 3 CH 2 4 CH CO 3 HO CH 4 CH 3 2 HCO 2 3 CH 2 5 CH OH, 3 H 2 HO 2 CO CH OH CO CH 3 O CH 4 3 CH 4 2 H 2 4 CH CH 3 3 CH 3 CH 2 2 CH 2 3 CH 4 CH 5 CH 3 H 2 CH 2 CH N H 2 2 H 2 H H C H 2 C C H 2 H 2 C CO H 2 HCN cosmic ray C 4 CH CN 3 C CH 3 HCN 3 3 CH 2 HCN NH 3 N HCO NH 2 CHCNH 2 5 CH CNH 3 HC N 11 HC N 9 HC N 7 HC N 5 HC N 3 CH NH 3 2 HCN 2 CHCN 2 5 CH CN 3 CH2NH CH3NH2 HCN

5 Diffus Intrstllar Clouds Translucnt (vis, UV) Mixtur of H & H 2 C C - DR limits chmistry n(h 2 ) ~ cm -3 [~10-18 atm] T ~ 50 K ζ Prsi Jos Frnandz Garcia

6 Diffus Cloud H 3 Chmistry Formation cosmic ray H 2 H 2 - H 2 H 2 H 3 H Rat = ζ [H 2 ] Dstruction H 3 - H H 2 or 3H Rat = k [H 3 ] [ - ] Stady Stat [H 3 ] ζ [H 2 ] = k [ - ] = ( s -1 ) ( cm 3 s -1 ) (2400) = 10-7 cm -3 Dnsity Indpndnt! Small!

7 Cygnus OB2 12 Surprising to dtct H 3 in a diffus cloud! Implis a path lngth of 1 kpc (3000 light-yars) Implis avrag dnsity ~ 20 cm -3 (too low) Pculiar sightlin? McCall, Gball, Hinkl, & Oka Scinc 279, 1910 (1998)

8 Othr Diffus Clouds, too! 1.01 HD R(1,1) u R(1,0) R(1,1) l Wavlngth (µm) GC IRS H 3 Column Dnsity (10 14 cm -2 ) HD Cyg OB2 5 HD WR 104 WR 121 HD χ 2 Ori P Cygni HD ζ Oph Cyg OB2 12 WR McCall, t al. ApJ 567, 391 (2002) E(B-V) (mag)

9 Big Problm with th Chmistry! 2-3 ordrs of magnitud!! Stady Stat: [H 3 ] ζ [H 2 ] = k [ - ] To incras th valu of [H 3 ], w nd: Highr ionization rat ζ Smallr rcombination rat constant k Smallr lctron fraction [ - ]/[H 2 ]

10 H 3 Dissociativ Rcombination Laboratory valus of k hav varid by 4 ordrs of magnitud! Thory unrliabl (until rcntly)... Problm (?): not masuring H 3 in ground stats

11 Storag Ring Masurmnts CRYRING 900 kv 12.1 MV 30 kv H3 20 ns 45 ns lctron bam H, H2 - Vry simpl xprimnt Complt vibrational rlaxation Control H3 - impact nrgy Rotationally hot ions producd No rotational cooling in ring

12 Brkly Suprsonic Ion Sourc Similar to sourcs for laboratory spctroscopy in Saykally group Gas inlt 2 atm H 2 Pulsd nozzl dsign Suprsonic xpansion lads to rapid cooling Discharg from ring lctrod downstram Pinhol flang/ground lctrod Solnoid valv Spctroscopy usd to charactriz ions Skimmr mployd to minimiz arcing to ring Insulating spacr Skimmr H V ring lctrod

13 R(1,0) R(1,1) u R(2,2) l 33 K (J,G) (2,0) (0,0) 151 K

14 Spctroscopy of H 3 Sourc Infrard Cavity Ringdown Lasr Absorption Spctroscopy Confirmd that H 3 producd is rotationally cold, as in intrstllar mdium McCall, t al. Natur 422, 500 (2003)

15 CRYRING Rsults Considrabl amount of structur (rsonancs) in th cross-sction k = cm 3 s -1 Factor of two smallr McCall, t al. Natur 422, 500 (2003)

16 Rcnt Thortical Work

17 Lingring Qustions (Minor) discrpancis with thory thory is wrong? xprimnt is wrong? high magntic filds (~300 Gauss) high lctron dnsity (~10 7 cm -3 ) prhaps ions don't stay cold? Major discrpancis with othr xprimnts nw stationary aftrglow masurmnts som flowing aftrglow masurmnts Prsnt storag-ring rsults ar prfrrd mor control ovr ion prparation conditions closst to intrstllar mdium rough agrmnt with thory

18 Back to th Intrstllar Clouds! Stady Stat: [H 3 ] ζ [H 2 ] = k [ - ] To incras th valu of [H 3 ], w nd: Highr ionization rat ζ Smallr rcombination rat constant k Smallr lctron fraction [ - ]/[H 2 ]

19 H 3 toward ζ Prsi [ - ]/[H 2 ] dtrmind McCall, t al. Natur 422, 500 (2003) N(C) from HST N(H 2 ) from Coprnicus Savag t al. ApJ 216, 291 (1977) Cardlli t al. ApJ 467, 334 (1996)

20 Back to th Intrstllar Clouds! Stady Stat: [H 3 ] ζ [H 2 ] = k [ - ] To incras th valu of [H 3 ], w nd: Highr ionization rat ζ Smallr rcombination rat constant k Smallr lctron fraction [ - ]/[H 2 ]

21 Implications for ζ Prsi N(H 3 ) L = [H 3 ] = ζ N(H 2 ) k N( - ) ζ L = k N(H 3 ) N( - ) ( cm 3 s -1 ) ( cm -2 ) ( ) N(H 2 ) ζ L = 8000 cm s -1 (solid) Adopt ζ= s -1 Adopt L=2.1 pc L = 85 pc ζ= s -1 n = 6 cm -3 (40x highr!)

22 Paramtrs: n=100 cm -3, L=4.2 pc, T=60 K Matchs all obsrvations within a factor of 3 ζ = s canonical valu OH not a problm H O O H ndothrmic by 227 K OH lowrd: T 60 K Still undrprdicts H 3 Proof of concpt

23 Futur Work Bttr xprimnts! Improvd spctroscopy of ion sourc Highr rsolution & highr snsitivity Bttr charactrization of ro-vib distribution Spctroscopy of xtractd ions? Mor obsrvations! Sarch for H 3 in mor sightlins "Dirct" prob of ionization rat Bttr obsrvations of ζ Prsi cloud Probs of cosmic-ray flux: C IV, H*? Othr atomic & molcular spcis (C I, CO)

24 Acknowldgmnts Millr Institut (Brkly) Takshi Oka (U. Chicago) Tom Gball (Gmini) Staff of UKIRT (Mauna Ka) Unitd Kingdom InfraRd Tlscop Staff of CRYRING (Stockholm) Chris Grn (Bouldr) Eric Hrbst (Ohio Stat) Mik Lindsay (UNC) Funding (Brkly): NSF AFOSR