IONS IN SPACE

“Ions are jolly little buggars, you can almost see them“ Ernest Rutherford

Simon Petriea

Diethard K. Böhmeb

aChemistry DepartmentAustralian National University, Canberra ACT0200, Australia

bDepartment of Chemistry Centre for Research in Mass Spectrometry

Centre for Research in Earth & Space ScienceYork University, Toronto, Canada

GRC, VenturaFebruary 27, 2007

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?

1. 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)

HISTORY OF DISCOVERYIon Year discovered Detection environments --------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------

CH+ 1941 many sourcesHCO+ 1970 TMC-1,Orion KL,Sgr B2 many sourcesN2H

+ 1974 TMC-1,Orion KL,Sgr B2 many sources

HCS+ 1981 TMC-1,Orion KL,Sgr B2HOCO+ 1981 Sgr B2 HOC+ 1983 Sgr B2, Orion Bar photodissociation regionHCNH+ 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 nebulaOrion Bar photodissociation region

HC3NH+ 1994 TMC-1

H3+ 1996 GL2136, W33A young stellar objects

Cyg OB2 diffuse interstellar mediumW33A dense molecular cloud

H2COH+ 1996 Orion KL,Sgr B2,W51 giant molecular cloud

CF+ 2006 Orion BarC6H

- 2006 TMC-1, IRC + 10216__________________________________________________________________________________________________________________________

Many more ions existin the imagination of astrochemists:

Negative ions.

PAH anions and cations.

Organometallic cations

Singly and Multiply charged PAHs, fullerenes..

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).

HCO+: 8 × 10-9

HCS+: 1 × 10-9

HCNH+: 3 × 10-9

N2H+: 5 × 10-10

HC3NH+: 1 × 10-10

HC3NH

Abundances of detected molecular ions within the cold dense cloud TMC-1

(number densities relative to that of predominant H2).

Fionization

≥ Σ fionization

Ffree electrons

≥ Σ fionization

(1.3x10-8)Problematic if ion census is incomplete or if electrons areattached!

NB: C6H-

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 theparent 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

NH3 NH4+ proton transfer

c-C3H2 c-C3H3+ proton transfer

H2, H3+

CH4, CH5+

CH+ C caution, sources other than PT to C

3. Ions in Molecular Synthesis

Small molecule synthesis is well understood, e.g. H2O

H+ + O O+ + HO+ + H2 OH+ + H

OH+ + H2 H2O+ + H

H2O+ + H2 H3O

+ + H

H3O+ + e H2O + H

The Ion Chemistry of Interstellar Clouds

David Smith

Chem. Rev. 1992, 92, 1473-1485

As is the ion synthesisof other small inorganic

and hydrocarbonmolecules:

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.

The Special Case of C6H-

But poorly understood is the ion synthesis of:

3a. Organometallics.

3b. Benzene, PAHs and related molecules.

3c. Amino acids and larger biological molecules.

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).

3a. Synthesis of organometallics.

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+

3b. Synthesis of benzene, PAHs, and …

Mg(HC3N)n-1+ + HC3N Mg(HC3N)n

+ + h, n 0

Mg(HC3N)n+ + e (HC3N)n + Mg

N N

NC

C

CC

N + Mg+ eCN

CN

CC

NN

Mg+

Milburn et al.,J. Am. Chem. Soc. 127 (2005)13070.

Tetracyanocyclooctatetraene (Tetracyanosemibullvalene)

Circumstellar Envelopes

Titan’s atmosphere

mCID

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 VERIFYINTERSTELLAR GLYCINE

L.E. Snyder et al.

Astrophys. J. 619: 914-930 (2005)

“We conclude that key lines necessary for an interstellar glycineidentification have not yet been found.”

3c. Synthesis of amino acids and larger biological molecules.

(Blagojevic et al., Mon. Not. R. Astron. Soc. 339 (2003) L7-L11.)

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

OH

O

NH2

0.8

0.6

0.4

0.2

0-10 -20 -30 -40

Nose cone potential /V

0

0.2

0.4

0.6

0.8

Gly+

CH2NH+

NH2CH2OH+

Gly+ CH2NH+

NH2CH2OH+

Rel

ativ

e in

ten

sity

GlyH+

CH2NH2+

GlyH+CH2NH2

+

GlyH+CH3COOH

0 0 -10 -20 -30

CO+ + NH2OH NH2OH+ + COCH5

+ + NH2OH (NH2OH)H+ + CH4

NH2,3OH+ + CH3COOH

CO+ + Gly / CH5+ + Gly

Gly+ CH2NH+ + (CO + H2O)GlyH+ CH2NH2

+ + (CO + H2O)

OH

O

NH2

mCID with Ar (0.14 Torr)

Relative enthalpies at 0K, ΔH0, for the formation of two isomers of protonated hydroxylamine from CH5

+ and NH2OH .

B3LYP/6-311++G(df,pd)CH4

ΔH0, kcal mol-1

50.4

24.3

0.0

CH4

TS

ΔH0, kcal mol-1

62.6 50.4

24.3

0.0

(Galina Orlova)

Potential energy landscape for the reaction between protonated hydroxyl amine and acetic acid to produce GlyH+

B3LYP/6-311++G(df,pd)

(Galina Orlova)

-54.1

23.124.3

TS1

H2O

-27.2

-18.8

0.0

ΔH0, kcal mol-1

PRC2

TS2

-13.7

Top: NH2OH+ + CH3CH2COOH

Middle:

CO+ + -Ala -Ala+ +CO

-Ala+ NH2CH2CHCO+ + H2O

Bottom:

CO+ + -Ala -Ala+ + CO

-Ala+ CH3CNH2+ +(CO+H2O)

OH

O

NH2

OH

O

NH2

-Ala+CH2CHNH

CH2NH+

Nose cone potential /V

-Ala+

-Ala+

CH2NH+

CH2NH+

CH3CH2COOH+NH3

NH2CH2CHCO+

NH2CH2CHCO+

CH3CH2COOH+

Rel

ativ

e in

ten

sity

0

0.2

0.4

0.6

0.8

0 -10 -20 -30 -40

0

0.2

0.4

0.6

0.8

0.2

0.4

0.6

0.8

0

-Ala+CH3CNH2

+

CH2NH+

Nose cone potential /V

-Ala+

-Ala+

CH2NH+

CH2NH+

CH3CH2COOH+NH3

NH2CH2CHCO+

NH2CH2CHCO+

CH3CH2COOH+

Rel

ativ

e in

ten

sity

0

0.2

0.4

0.6

0.8

0 -10 -20 -30 -40

0

0.2

0.4

0.6

0.8

0.2

0.4

0.6

0.8

0

-Ala+CH2CHNH

CH2NH+

Nose cone potential /V

-Ala+

-Ala+

CH2NH+

CH2NH+

CH3CH2COOH+NH3

NH2CH2CHCO+

NH2CH2CHCO+

CH3CH2COOH+

Rel

ativ

e in

ten

sity

0

0.2

0.4

0.6

0.8

0 -10 -20 -30 -40

0

0.2

0.4

0.6

0.8

0.2

0.4

0.6

0.8

0

-Ala+CH3CNH2

+

CH2NH+

Nose cone potential /V

-Ala+

-Ala+

CH2NH+

CH2NH+

CH3CH2COOH+NH3

NH2CH2CHCO+

NH2CH2CHCO+

CH3CH2COOH+

Rel

ativ

e in

ten

sity

0

0.2

0.4

0.6

0.8

0 -10 -20 -30 -40

0

0.2

0.4

0.6

0.8

0.2

0.4

0.6

0.8

0

mCID with Ar (0.14 Torr)

Potential energy landscape for the reaction between protonated hydroxyl amine and propanoic acid to produceβ-AlaH+ (solid line) and α-AlaH+ (dotted line)

(chondrite meteorites,aggregates of interstellar dust, 40%β)

B3LYP/6-311++(df,pd)

(Galina Orlova)H2O

TS1

TS2-β

ΔH0, kcal mol-1

12.4

24.3

-65.3

β-AlaH+

TS2-α

17.4

0.0

-59.5

α-AlaH+

-27.2-14.5

-19.4

TS2-α TS2-β

NH3(s) + H2O(s) NH2OHhv hv NO + 3H

hv, heat

NH2OH

Interstellar ice

Interstellar gas

hv/A+ RH+

NH2OH2+NH2OH+

CH3COOHCH3CH2COOH

CH3COOHCH3CH2COOH

NH2CH2COOH+

NH2CH2CH2COOH+

NH3CH2COOH+

NH3CH2CH2COOH+

-H2O-H2O

MM+

NH2CH2COOHNH2CH2CH2COOH

e-

H

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.)

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+ + H2OFe+CH3CONHCH2COOH + NH2OH ? (too complicated)

Fe+NH2CH2CONHCH2COOH + H2Odiglycine, a dipeptide

M+(Gly)n + CH3COOH + NH2OH M+(Gly)n+1 + H2O(M+ assembles the protein) larger and larger peptidesVoislav Blagojevic: Ions, Biomolecules and Catalysis: SIFTing for the Origins of Life, York U, 2005

4. Ions as Catalysts.

Ions as catalysts of neutral reactions

Atom (Molecule) TransportM+ + XO MO+ + XMO+ + Y M+ + YO______________________________________________________

XO + Y YO + X

Bond-Activation CatalysisFe+ + C6H6 Fe+C6H6 + hFe+C6H6 + O2 Fe+ + (C6H6O2)_______________________________________________________________________________________________________________________________________

C6H6 + O2 (C6H6O2) + h (see example)

Bond-Formation (Recombination) CatalysisM+(grain) + O MO+(grain)MO+(grain) + CO M+(grain) + CO2______________________________________________________________________________________________

O + CO CO2

M+ + C6H6 MC6H6+

MC6H6+ + O2 M+

+ (C6H6O2) -----------------------------------------C6H6 + O2 (C6H6O2)

(M = Fe, Cr, Co)

Catalytic oxidation of benzene

catechol

0.0

0.2

0.4

0.6

0.8

1.0

0.0

0.2

0.4

0.6

0.8

1.0

TiBz+

VBz+

CrBz+

MnBz+

FeBz+

CoBz+

NiBz+

CuBz+ ZnBz

+

ZrBz+NbBz+ MoBz+ TcBz+ RuBz+ RhBz+ PdBz+ AgBz+ CdBz+

0.0

0.2

0.4

0.6

0.8

1.0

TaBz+HfBz+ WBz+ ReBz+ OsBz+ IrBz+ PtBz+ AuBz+ HgBz+

O2 addition

O atom transfer

addition/dehydration

metal abstraction

benzene abstraction

ligand switching

acetylene elimination

Bra

nch

ing

Ra

tios

an

d k

/kc

NR

ScBz+

YBz+

LaBz+

NA

not available or non-reaction

NRNA

+ O2

OH

C O + H2O

OO

+ H2

OHHO

+ O H = 16.8±0.3 kcal mol-1

H = 62.5±2.5 kcal mol-1

H = -44.8±1.1 kcal mol-1

O + O

O

O H = 29.5±0.1kcal mol-1

OO

H = 14.4±0.1 kcal mol-1

CHO

CHOH = -52.4±0.1 kcal mol-1

H = -52.6±1.1 kcal mol-1

H = -84.8±1.1 kcal mol-1

Caraiman & BohmeJ. Phys. Chem. A 2002, 106,9705-17.

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-glycineM+CH3CONHCH2COOH + NH2OH

M+ + NH2CH2CONHCH2COOH + H2O____________________________________________________________________________________________________________________________________________________________

CH3CONHCH2COOH + NH2OH NH2CH2CONHCH2COOH + H2ON-acetyl-glycine diglycine, a dipeptide

V. Blagojevic, Ph.D. Dissertation, York U., 2005

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

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”

Possible Sources of Molecular Dications1. 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).

“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 ofexcess energy, -(ΔH + δ) :

ET (XH+) = (2 δ – ΔH) x (mC60Hn/(mC60Hn+mXH)/3

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+ + H Ea ≤ 1 kcal mol-1

C6H2+ + e C6H + e C6H-

N C C CH+ +

+ N C C CH+ N C C CH+

N C C CH

+

++

N C C CHNCCHC

+ +·

NC

NC

C

C C

C

H

H

+•

“Molecular Docks”

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 thesubstituent and so provides a new atomic site for further reaction, with

ultimate charge separation. 

C602+ + 2 HC3N C60

+• + c-(HC3N)2+•

Milburn et al, JPC A 103 (1999) 7528.

Isomers of (HC3N)2+•

At B3LYP/6-31+G(d) (top numbers) and B3LYP/6-311++G-(2df,p) (bottom numbers)

CHEMISTRYLEFT:

C602+ + HC3N C60(HC3N)2+

C60(HC3N)2+ + HC3N C60

+ + (HC3N)2+

RIGHT:

HC3N+ + HC3N (HC3N)2+

mCIDLEFT:

(HC3N)2+ HC6N2

+ + H

H2C5N+ + CN

RIGHT:

(HC3N)2+ HC3N+ + HC3N

HC3N+ HC2+ + CN

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.

Greg Koyanagi Janna AnichinaVoislav Blagojevic Michael JarvisAndrea DasicTuba Gozet Svitlana ShcherbynaZhao XiangPing ChengProf. Kee LeeJason XuSam HaririVitali LavrovLise HuynhSoroush Seifi

Acknowledgments

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.