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Molecular Ions in Space: Detection, Information Content, and Synthesis

Explore the fascinating world of molecular ions in space, from their detection and information content to their role in molecular synthesis. Learn about the history of their discovery and the potential for ion synthesis of various organic molecules.

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Molecular Ions in Space: Detection, Information Content, and Synthesis

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  1. IONS IN SPACE “Ions are jolly little buggars, you can almost see them“ Ernest Rutherford Simon Petriea Diethard K. Böhmeb aChemistry Department Australian National University, Canberra ACT0200, Australia bDepartment of Chemistry Centre for Research in Mass Spectrometry Centre for Research in Earth & Space Science York University, Toronto, Canada GRC, Ventura February 27, 2007

  2. SCOPE 1. Molecular Ions Detected So Far. 2. Information Content of Detected Ions. 3. Ions in Molecular Synthesis. 4. Ions as Catalysts and Victims of Catalysts. 5. A Chemical Role for Multiply-Charged Ions?

  3. MOLECULAR IONS DETECTED SO FAR • CH+ (vis), CF+, CO+, NO+, SO+ • H3+ (IR), HCO+, COH+, HCS+, N2H+ • H3O+, HOCO+, HCNH+, • H2COH+ • HC3NH+ • C6H- • NB: (15 + 1 = 16), all but one positive, 2 isomeric, • none multiply charged, no organometallic ions • Observational biases: • - need to know what to look for (spectroscopy), • - need to know where to look (location), • - need enough to look at (abundance)

  4. HISTORY OF DISCOVERY Ion Year discovered Detection environments -------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- CH+ 1941 many sources HCO+ 1970 TMC-1,Orion KL,Sgr B2 many sources N2H+ 1974 TMC-1,Orion KL,Sgr B2 many sources HCS+ 1981 TMC-1,Orion KL,Sgr B2 HOCO+ 1981 Sgr B2 HOC+ 1983 Sgr B2, Orion Bar photodissociation region HCNH+ 1986 TMC-1,Sgr B2 H3O+ 1986 Orion KL,Sgr B2 SO+ 1992 IC 443G shocked molecular clump Orion Bar photodissociation region CO+ 1993 NGC7027 planetary nebula Orion Bar photodissociation region HC3NH+ 1994 TMC-1 H3+ 1996 GL2136, W33A young stellar objects Cyg OB2 diffuse interstellar medium W33A dense molecular cloud H2COH+ 1996 Orion KL,Sgr B2,W51 giant molecular cloud CF+ 2006 Orion Bar C6H- 2006 TMC-1, IRC + 10216 __________________________________________________________________________________________________________________________

  5. Many more ions exist in the imagination of astrochemists: Negative ions. PAH anions and cations. Organometallic cations Singly and Multiply charged PAHs, fullerenes..

  6. 2. INFORMATION CONTENT OF IONS a. Ions as Measures of Electron Density Ions are susceptible to spectroscopic detection, but free electrons are not. - When approximate electro-neutrality prevails, the determination of molecular ion abundance can provide a partial picture of the free-electron abundance. - Electron density is thought to determine the rate of cloud collapse, and therefore of star formation. Molecular ion measurements can provide an assay of the degree of ionization and the electron density (and so insight into the rate of star formation).

  7. Abundances of detected molecular ions within the cold dense cloud TMC-1 (number densities relative to that of predominant H2). Fionization ≥Σfionization Ffree electrons ≥Σfionization (1.3x10-8) HC3NH Problematic if ion census is incomplete or if electrons are attached! NB:C6H-

  8. 2. INFORMATION CONTENT OF IONS (cont’d) b. Ions as Tracers of Atoms and Molecules The detection of an ion can provide a ‘signature’ of the parent of the ion when the parent is ‘invisible’. (invisible to radioastronomers, no dipole moment) visible invisible connection N2H+ N2 proton transfer HOCO+CO2 proton transfer NH3NH4+ proton transfer c-C3H2c-C3H3+ proton transfer H2, H3+ CH4, CH5+ CH+ Ccaution,sources other than PT to C

  9. 3. Ions in Molecular Synthesis Small molecule synthesis is well understood, e.g. H2O H+ + O  O+ + H O+ + H2 OH+ + H OH+ + H2 H2O+ + H H2O+ + H2  H3O+ + H H3O+ + e  H2O + H

  10. As is the ion synthesis of other small inorganic and hydrocarbon molecules: The Ion Chemistry of Interstellar Clouds David Smith Chem. Rev. 1992, 92, 1473-1485

  11. The Special Case of C6H- C6H + e  C6H- + h EA(C6H) = 3.8 eV 7 atoms PAH + e  PAH- + h high EA, many atoms PAH- + C6H  PAH + C6H- C6H- + H  C6H2 + e NB: C4H- would be very interesting because C4H is massively abundant in IRC+10216.  The cyanopolyynyl radicals like C5N are also very promising because they have EA values of 4 eV or more, so attachment is very favourable, but these radicals aren't as abundant as CnH radicals.

  12. But poorly understood is the ion synthesis of: • 3a. Organometallics. • 3b. Benzene, PAHs and related molecules. • 3c. Amino acids and larger biological molecules.

  13. 3a. Synthesis of organometallics. A simple network of probable or possible reaction pathways for reactions of Fe+ with hydrocarbons (principally C2H2 and C4H2) and with CO under dense interstellar cloud conditions. Speculative dissociative recombination pathways are indicated by arrows featuring dotted lines; major reaction pathways are shown by bold arrows. (Petrie et al., Astrophys. J. 476:191-194, 1997).

  14. 3b. Synthesis of benzene, PAHs, and … C+ + C3H  C4+ + H C4+ + H2  C4H2+ + H C4H2+ + H  C4H3++ h C4H3+ + C2H2 (or + C2H3)  C6H5++ h (or + H) C6H5+ + H2 C6H7++ h C6H7+ + e  C6H6+ H Fe(C2H2)2+ + C2H2  FeC6H6+ + h Fe C6H6+ + e  Fe + C6H6 C6H6+ + C4H2  C10H8++ h C10H8+ + M  C10H8+ M+

  15. Mg(HC3N)n-1+ + HC3N  Mg(HC3N)n+ + h, n  0 Mg(HC3N)n+ + e  (HC3N)n + Mg Tetracyanocyclooctatetraene (Tetracyanosemibullvalene) Circumstellar Envelopes Titan’s atmosphere mCID Milburn et al., J. Am. Chem. Soc. 127 (2005)13070.

  16. 3c. Synthesis of amino acids and larger biological molecules. INTERSTELLAR GLYCINE Y.-J. Kuan, S.B. Charnley, et al. Astrophys. J. 593: 848-867 (2003) “…27 glycine lines were detected ..in one or more sources..” A RIGOROUS ATTEMPT TO VERIFY INTERSTELLAR GLYCINE L.E. Snyder et al. Astrophys. J. 619: 914-930 (2005) “We conclude that key lines necessary for an interstellar glycine identification have not yet been found.”

  17. Unsuccessful attempts: CH3NH2+ + HCOOH CH3NH2+ + CO2 CH3NH2+ + CO + H2O NH3+ + CH3COOH CH3COOH+ + NH3 N-O bond formation is preferred over C-C and N-C bond formation. NH2OH2+ + CH3COOH OH+O bonding allows N-C bond formation (Blagojevic et al., Mon. Not. R. Astron. Soc. 339 (2003) L7-L11.)

  18. GlyH+ CH2NH+ 0.8 0.6 Gly+ CH2NH2+ 0.4 Relative intensity GlyH+CH3COOH NH2CH2OH+ 0.2 CH2NH+ CH2NH2+ 0 Gly+ GlyH+ NH2CH2OH+ 0 0 -10 -20 -30 Nose cone potential /V 0.8 0.6 0.4 0.2 0 -10 -20 -30 -40 CO+ + NH2OH  NH2OH+ + CO CH5+ + NH2OH  (NH2OH)H+ + CH4 NH2,3OH+ + CH3COOH CO+ + Gly / CH5+ + Gly Gly+ CH2NH+ + (CO + H2O) GlyH+ CH2NH2+ + (CO + H2O) mCID with Ar (0.14 Torr)

  19. Å - - 1 1 Δ Δ H H kcal kcal mol mol Relative enthalpies at 0K, ΔH0, for the formation of two isomers of protonated hydroxylamine from CH5+ and NH2OH . B3LYP/6-311++G(df,pd) 0, 0, Å Å 0.0 0.0 Å Å TS 62.6 50.4 50.4 Å Å 24.3 24.3 CH Å CH 4 Å 4 (Galina Orlova)

  20. ΔH0, kcal mol-1 TS2 24.3 23.1 0.0 -13.7 -18.8 -27.2 TS1 -54.1 PRC2 H2O Potential energy landscape for the reaction between protonated hydroxyl amine and acetic acid to produce GlyH+ B3LYP/6-311++G(df,pd) (Galina Orlova)

  21. mCID with Ar (0.14 Torr) Top: NH2OH+ + CH3CH2COOH Middle: CO+ + -Ala -Ala+ +CO -Ala+ NH2CH2CHCO+ + H2O Bottom: CO+ + -Ala -Ala+ + CO -Ala+  CH3CNH2+ +(CO+H2O)

  22. ΔH0, kcal mol-1 TS2-α TS2-β TS2-α 17.4 24.3 TS2-β 12.4 0.0 -14.5 -19.4 -27.2 TS1 -59.5 -65.3 α-AlaH+ β-AlaH+ H2O Potential energy landscape for the reaction between protonated hydroxyl amine and propanoic acid to produce β-AlaH+ (solid line) and α-AlaH+ (dotted line) (chondrite meteorites, aggregates of interstellar dust, 40%β) B3LYP/6-311++(df,pd) (Galina Orlova)

  23. NH2CH2COOH NH2CH2CH2COOH M+ H M e- NH3CH2COOH+ NH3CH2CH2COOH+ NH2CH2COOH+ NH2CH2CH2COOH+ CH3COOH CH3CH2COOH CH3COOH CH3CH2COOH -H2O -H2O hv/A+ RH+ NH2OH+ NH2OH NH2OH2+ Interstellar gas hv, heat Interstellar ice hv hv NH3(s) + H2O(s) NH2OH NO + 3H M and A represent any neutral atom / molecule with a suitable IE. RH+ represents a proton carrier with PA(R) < PA(NH2OH). (Blagojevic et al., Mon. Not. R. Astron. Soc. 339 (2003) L7-L11.)

  24. Limits to growth? Peptides/Proteins: (CI conditions: glutamic acid / methionine) (NH2CHRCOOH)H+ + NH2CHRCOOH  (NH2CHRCONHCHRCOOH)H+ + H2O Wincel, Fokkens, Nibbering, Rapid Comm MS 14 (2000) 135. (NH2CH2COOH)H+ +CH3COOH(CH3CONHCH2COOH)H++H2O protonated N-acetyl-glycine (CH3CONHCH2COOH)H+ + NH2OH  no (clusters) (NH2CH2CONHCH2COOH)H+ + H2O Fe+CH3CONHCH2COOH+ NH2OH  ? (too complicated) Fe+NH2CH2CONHCH2COOH+ H2O diglycine, a dipeptide M+(Gly)n + CH3COOH + NH2OH  M+(Gly)n+1 + H2O (M+ assembles the protein) larger and larger peptides Voislav Blagojevic: Ions, Biomolecules and Catalysis: SIFTing for the Origins of Life, York U,2005

  25. 4. Ions as Catalysts. Ions as catalysts of neutral reactions Atom (Molecule) Transport M+ + XO  MO+ + X MO+ + Y  M+ + YO ______________________________________________________ XO + Y  YO + X Bond-Activation Catalysis Fe+ + C6H6 Fe+C6H6 + h Fe+C6H6 + O2 Fe+ + (C6H6O2) _______________________________________________________________________________________________________________________________________ C6H6 + O2 (C6H6O2) + h(see example) Bond-Formation (Recombination) Catalysis M+(grain) + O  MO+(grain) MO+(grain) + CO  M+(grain) + CO2 ______________________________________________________________________________________________ O + CO  CO2

  26. Catalytic oxidation of benzene M+ + C6H6 MC6H6+ MC6H6+ + O2 M++ (C6H6O2) ----------------------------------------- C6H6 + O2 (C6H6O2) (M = Fe, Cr, Co) Caraiman & Bohme J. Phys. Chem. A2002, 106, 9705-17. catechol

  27. C602+ + H  C60H2+ + h -67 kcal mol-1 C60H2+ + H  C602+ + H2 -33 kcal mol-1 ____________________________________________________________________ H + H  H2 Petrie et al, Astron. Astrophys. 271 (1991) 662. M+ +CH3CONHCH2COOH  M+CH3CONHCH2COOH +h N-acetyl-glycine M+CH3CONHCH2COOH+ NH2OH  M+ + NH2CH2CONHCH2COOH+ H2O ____________________________________________________________________________________________________________________________________________________________ CH3CONHCH2COOH + NH2OH  NH2CH2CONHCH2COOH+ H2O N-acetyl-glycine diglycine, a dipeptide V. Blagojevic, Ph.D. Dissertation, York U., 2005

  28. 4. Ions as Victims of Catalysts. Neutrals as catalysts of ion isomerization: Proton-Transport Catalysis HOC+ + H2 H3+ + CO H3+ + CO  HCO+ + H2 ________________________________________________________ HOC+ HCO+ Neutrals as catalysts of ion neutralization Fe+ + CmHn Fe+CmHn + h Fe+CmHn+ + e  Fe + CmHn ______________________________________________________________________ Fe+ + e  Fe + h M+ + grain  M+(grain) + h (?) M+(grain) + e  M + grain ___________________________________________________________________________ M+ + e  M

  29. 5. A Unique Chemical Role for Multiply-Charged Ions? Multiply charged ions: 1. Provide excess energy for products, 2. Provide electrostatic energy for reactants. “molecular cannons” “molecular docks”

  30. Possible Sources of Molecular Dications 1. Sequential Photoionization X + h X+ + e X+ + h  X2+ + e - More important within diffuse regions (since the penetration of UV radiation within dense clouds is poor). Need IE(X+) < IE(H). 2. Electron Transfer/ Electron Detachment He+ + X  X2+ + He + e - Need IE(X) + IE(X+) < IE(He) (24.587 eV). - More feasible with larger molecules such as PAHs and fullerenes. - Observed with naphthalene and C60. 3. Cosmic-ray Ionization X + c.r.  X2+ + c.r.’ + 2e - Has no energy restrictions, but efficiency is not known. - Likely to be of some significance throughout dense IS clouds (since cosmic rays can penetrate deep within such clouds).

  31. “Molecular Cannons” • Charge separation reactions of heavy multiply-charged • cations with light molecules can lead to the production of • internally cold, but translationally hot, ions • - and so provide a driving force for the subsequent • occurrence of ion/neutral reactions! • Petrie S, Bohme DK MNRAS 268 (1994) 103-108. For partitioning of all of Coulombic repulsion, δ, into translational excitation of XH+ and statistical partitioning of excess energy, -(ΔH + δ) : ET (XH+) = (2 δ – ΔH) x (mC60Hn/(mC60Hn+mXH)/3

  32. e.g. C602+ and C60H2+ as molecular canons: C602+ + C6H6 C60+ + C6H6+ ET = 40 kcal mol-1 C60H2+ + NH3 C60+ + NH4+ ET = 53 kcal mol-1 ET often 40 to 50 kcal mol-1 ! More favorable with heavy dications, but applicable to all molecular dications. e.g. Subsequent driven ion/molecule reactions: C60H2+ + C6 C60+ + C6H+ C6H+ + H2  C6H2+ + HEa ≤ 1 kcal mol-1 C6H2+ + e  C6H + e  C6H-

  33. + + + + + + + N C C C H + H C C C N + · + +• “Molecular Docks” Milburn et al, JPC A 103 (1999) 7528. C602+ + 2 HC3N  C60+• + c-(HC3N)2+• • Desirable Attributes: • Provide atomic site (e.g. C) for covalent bonding. • Provide sufficient charge for electrostatic attraction to overcome rehybridization energy required for bonding. • Provide the intramolecular Coulomb repulsion necessary to propagate a charge to the terminus of thesubstituent and so provides a new atomic site for further reaction, with ultimate charge separation.

  34. Isomers of(HC3N)2+• At B3LYP/6-31+G(d) (top numbers) and B3LYP/6-311++G-(2df,p) (bottom numbers)

  35. CHEMISTRY LEFT: C602+ + HC3N  C60(HC3N)2+ C60(HC3N)2+ + HC3N  C60+ + (HC3N)2+ RIGHT: HC3N++ HC3N  (HC3N)2+ mCID LEFT: (HC3N)2+ HC6N2+ + H  H2C5N+ + CN RIGHT: (HC3N)2+ HC3N++ HC3N HC3N+HC2+ + CN

  36. Parting Messages…. • A large number of molecular ions remain to be discovered • in space (given what is known about ion chemistry). • This includes organometallic and multiply-charged cations • which can have a rich chemistry. • The role of ion catalysis in interstellar chemistry is yet to • be appreciated, should increase the importance of ions in • the synthesis of molecules in space. • Space is an ideal medium in which molecular cannons can • make a chemical difference. • Molecular dock chemistry also is very attractive and may • involve a variety of multiply-charged molecules or particles • with bonding sites.

  37. Acknowledgments Greg Koyanagi Janna Anichina Voislav Blagojevic Michael Jarvis Andrea Dasic Tuba Gozet Svitlana Shcherbyna Zhao Xiang Ping Cheng Prof. Kee Lee Jason Xu Sam Hariri Vitali Lavrov Lise Huynh Soroush Seifi

  38. Special thanks to Simon Petrie! “Ions in Space” S. Petrie, D.K. Bohme Mass Spectrometry Reviews 26 (2007) 258-280. “Mass Spectrometric Approaches to Interstellar Chemistry” S. Petrie, D.K. Bohme in “Modern Methods in Mass Spectrometry” C.A. Shalley (ed.) Springer Verlag, Berlin, 2003.

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