June 21, th International Symposium on Molecular Spectroscopy Detection of FeCN (X 4  i ) in the Circumstellar Envelope of IRC Lindsay N. Zack, DeWayne T. Halfen, and Lucy M. Ziurys Department of Chemistry and Biochemistry, Department of Astronomy and Steward Observatory, Arizona Radio Observatory, University of Arizona

June 21, th International Symposium on Molecular Spectroscopy AGB star Age = 10, ,000 yr Distance = 150 pc (31 × 10 6 AU) High mass-loss rate (3 × M  yr -1 ) Most-studied star in mm observations Rich chemistry, 60+ molecules IRC+10216

June 21, th International Symposium on Molecular Spectroscopy Metal-containing molecules in the ISM Seen in circumstellar envelopes (e.g. IRC+10216, VY CMa) and proto-planetary nebulae (e.g. CRL618, CRL2688) Halides and Cyanides common carriers in C-rich sources – e.g. NaCl, AlCl, KCl, KCN, MgNC, AlNC Oxides and Hydroxides carriers in O-rich sources – AlO, AlOH Optical spectra of stars – TiS, TiO, YS, ZrS

June 21, th International Symposium on Molecular Spectroscopy Cosmic Abundances Iron Peak Na-, Mg-, Al-, and K-bearing molecules detected in IRC Fe-containing molecules??

June 21, th International Symposium on Molecular Spectroscopy Iron Abundance Cosmic abundance: Fe/H ~ 3 × – Order of magnitude greater than Na, Al, and K Depletion – Most of iron condensed into grains? (e.g. Savage & Bohlin 1979) – Only 1% in gas phase in diffuse clouds (Jensen & Snow 2007) Fe in IRC (Mauron & Huggins 2010) – Gas phase abundance N(Fe I + Fe II )/N(H) ~1.7 × 10 -7

June 21, th International Symposium on Molecular Spectroscopy Previous Searches for Fe-bearing molecules FeO – Merer et al. (1982) Survey of several stars, molecular clouds, and planetary nebulae Upper limit: N tot < 2 × cm -2 – Walmsley et al. (2002) Tentative detection of J = 5  4 transition in  = 4 ladder toward Sgr B2(M) with IRAM 30 m telescope, but no other transitions observed FeCO – Kagi et al. (1997) Survey of star-forming regions and IRC Upper limits: 8 × < N tot < 3 × cm -2

June 21, th International Symposium on Molecular Spectroscopy FeCN (X 4  i ) in the Lab 5 year laboratory search by Ziurys group (Mike Flory) – Uncertainty about lowest energy isomer (FeNC vs. FeCN) and ground state ( 6  i or 4  i ) Determined accurate rest frequencies for astronomical search Flory & Ziurys, submitted

June 21, th International Symposium on Molecular Spectroscopy Observations ARO 12m telescope on Kitt Peak Nine transitions from GHz ~100+ hours per transition rms noise level < 1 mK Search for FeCN began April 2007 KP 12m … it’s gotta be there…

June 21, th International Symposium on Molecular Spectroscopy FeCN definitively detected in IRC Emission at all nine transitions observed Three “clean” transitions (84, 100, and 108 GHz) Confirmation on IRAM 30m in Spain Zack et al Cernicharo et al Results IRAM FeCN observed at IRAM 30m telescope in Spain

June 21, th International Symposium on Molecular Spectroscopy First definitive detection of an iron-containing molecule in the ISM Abundances of Cyanides in IRC Species Source Size (") Observed AbundanceReference KCN306 × Pulliam et al NaCN52 × Guelin et al 1993; Highberger & Ziurys 2003 AlNC153 × Ziurys et al MgCN407 × Ziurys et al MgNC409 × Guelin et al. 1993; Highberger & Ziurys 2003 FeCN302-7 × Zack et al. 2011

June 21, th International Symposium on Molecular Spectroscopy Possible Formation Pathways Radiative Association / Dissociative Electron Recombination Fe + + HC n N  FeNC n H + + h (k = 6.6 × (T/300) cm 3 s-1) FeNC n H + + e -  FeNC + C n-1 H (followed by isomerization to FeCN) Strong possibility of FeNC, as well. Insertion (k = cm 3 s -1 ) Fe + + HC n N  NCFeC n-1 H + + h NCFeC n-1 H + + e -  FeCN + C n-1 H Radical-radical (k = cm 3 s -1 ): Fe + MgNC  FeCN + Mg FeCN formed in outer envelope of IRC Fast reactions/ low barriers Ions and radicals Petrie 1997; Petrie et al. 1996; Dunbar & Petrie 2002; Cordiner & Millar 2009

June 21, th International Symposium on Molecular Spectroscopy Conclusions FeCN is the 6 th metal cyanide detected in IRC N tot = 8.6 × cm -2 ; T rot = 21 K; [FeCN]/[H 2 ] ~ 2-7 × First transition-metal bearing molecule in ISM Iron is not completely depleted in the ISM Other Fe-containing molecules could be detectable Reaction rates and formation pathways for iron-bearing molecules need to be studied by theoreticians and experimentalists

June 21, th International Symposium on Molecular Spectroscopy Acknowledgements Prof. Lucy Ziurys Ziurys Group ARO telescope operators, engineers, and staff NSF and NASA