Transcript Document

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
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+
C6HNB: (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)
Ion
HISTORY OF DISCOVERY
Year discovered
Detection environments
------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- -------------------
CH+
HCO+
N 2H +
HCS+
HOCO+
HOC+
HCNH+
H 3 O+
SO+
1941
1970
1974
1981
1981
1983
1986
1986
1992
CO+
1993
HC3NH+
H 3+
1994
1996
H2COH+
CF+
C 6H -
1996
2006
2006
many sources
many sources
many sources
TMC-1,Orion KL,Sgr B2
TMC-1,Orion KL,Sgr B2
TMC-1,Orion KL,Sgr B2
Sgr B2
Sgr B2, Orion Bar
photodissociation region
TMC-1, Sgr B2
Orion KL, Sgr B2
IC 443G
shocked molecular clump
Orion Bar
photodissociation region
NGC7027
planetary nebula
Orion Bar
photodissociation region
TMC-1
GL2136, W33A
young stellar objects
Cyg OB2
diffuse interstellar medium
W33A
dense molecular cloud
Orion KL,Sgr B2,W51 giant molecular cloud
Orion Bar
TMC-1, IRC + 10216
__________________________________________________________________________________________________________________________
Many more ions exist
in 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).
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
HCO+: 8 × 10-9
HC3NH
+
-10
N2H : 5 × 10
HCS+: 1 × 10-9
HCNH+: 3 × 10-9
HC3NH+: 1 × 10-10
(1.3x10-8)
Problematic if ion
census is incomplete
or if electrons are
attached!
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 the
parent of the ion when the parent is ‘invisible’.
(invisible to radioastronomers, no dipole moment)
visible
N2H+
HOCO+
invisible
N2
CO2
connection
proton transfer
proton transfer
NH3
NH4+
proton transfer
c-C3H2
c-C3H3+
proton transfer
H2, H3+
CH+
CH4, CH5+
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+ + H 2 
OH+ + H2 
H 2O + + H 2 
H 3O + + e 
O+ + H
OH+ + H
H 2O + + H
H 3O + + H
H 2O + H
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
The Special Case of C6HC6H + 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.
But poorly understood is the ion synthesis of:
3a. Organometallics.
3b. Benzene, PAHs and related molecules.
3c. Amino acids and larger biological molecules.
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).
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+
Mg(HC3N)n-1+ + HC3N  Mg(HC3N)n+ + h, n  0
Mg(HC3N)n+ + e  (HC3N)n + Mg
Mg+
NC
NC
CN
NC
+e
CN
mCID
NC
CN
CN
+ Mg
Tetracyanocyclooctatetraene
(Tetracyanosemibullvalene)
Circumstellar
Envelopes
Titan’s atmosphere
Milburn et al.,
J. Am. Chem. Soc.
127 (2005)13070.
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.”
Unsuccessful attempts:
O
CH3NH2+ + HCOOH
CH3NH2+ + CO2
CH3NH2+ + CO + H2O
NH2
NH3+ + CH3COOH
CH3COOH+ + NH3
OH
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.)
CO+ + NH2OH  NH2OH+ + CO
CH5+ + NH2OH 
(NH2OH)H+ + CH4
NH2,3OH+ + CH3COOH
mCID with Ar (0.14 Torr)
0.8
GlyH+
CH2NH+
Relative intensity
0.6
Gly+
0.4
CO+ + Gly / CH5+ + Gly
O
CH2NH2+
0.2
0
0.8
GlyH+CH3COOH
NH2CH2OH+
Gly+
CH2NH+
CH2NH2+
GlyH+
0.6
NH2
0.4
OH
Gly+  CH2NH+ + (CO + H2O)
GlyH+  CH2NH2+ + (CO + H2O)
0.2
0
0
NH2CH2OH+
-10
-20
-30
-40 0
-10
-20
Nose cone potential /V
-30
ΔH0, kcal mol-1
Relative enthalpies at 0K,
ΔH0, for the formation of
two isomers of protonated
hydroxylamine from CH5+
and NH2OH .

0.0
TS
62.6

50.4



24.3
24.3
CH4 

CH4
B3LYP/6-311++G(df,pd)
(Galina Orlova)
ΔH0, kcal mol-1
Potential energy
landscape for the
reaction between
protonated
hydroxyl amine and
acetic acid to
produce GlyH+
TS2
24.3
23.1
0.0
-13.7
-18.8
-27.2
TS1
-54.1
B3LYP/6-311++G(df,pd)
PRC2
H2O
(Galina Orlova)
mCID with Ar (0.14 Torr)
0.8
CH3CH2COOH+NH3
0.6
CH3CH2COOH+
Top:
NH2OH+ + CH3CH2COOH
NH2CH2CHCO+
CH2NH+
0.4
Middle:
-Ala+
0.2
CO+ + -Ala -Ala+ +CO
0
O
-Ala+
NH2
OH
-Ala+  NH2CH2CHCO+ + H2O
Bottom:
CO+ + -Ala -Ala+ + CO
Relative intensity
0.8
CH2NH+
0.6
0.4
NH2CH2CHCO+
0.2
0
+
CH32CNH
CHNH
2
-Ala+
0.8
O
0.6
NH2
0.4
OH
0.2
-Ala+  CH3CNH2+ +(CO+H2O)
CH2NH+
0
0
-10
-20
-30
Nose cone potential /V
-40
ΔH0, kcal mol-1
TS2-α
TS2-β
TS2-α
17.4
24.3
TS2-β
12.4
0.0
-14.5
-27.2
-19.4
TS1
-59.5
(chondrite meteorites,
aggregates of
interstellar dust, 40%β)
-65.3
α-AlaH+
β-AlaH+
Potential energy
landscape for the
reaction between
protonated
hydroxyl amine and
propanoic acid to
produce
β-AlaH+ (solid line)
and α-AlaH+ (dotted
line)
H2O
B3LYP/6-311++(df,pd)
(Galina Orlova)
NH2CH2COOH
M+ NH2CH2CH2COOH
H
M
e-
NH2CH2COOH+
NH2CH2CH2COOH+
NH3CH2COOH+
NH3CH2CH2COOH+
CH3COOH
-H2O CH3CH2COOH
hv/A+
NH2OH+
Interstellar gas
Interstellar ice
NH3(s) + H2O(s) hv
CH3COOH
CH3CH2COOH -H2O
RH+
NH2OH2+
NH2OH
hv, heat
NH2OH
hv
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.)
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
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
1.0
+
0.8
ScBz+ TiBz
+
VBz
+
+
+
+
CrBz MnBz FeBz CoBz
0.6
+
+
+
NiBz CuBz ZnBz
0.4
M+ + C6H6  MC6H6+
0.2
Branching Ratios and k/kc
Catalytic oxidation of benzene
0.0
1.0
0.8
+
ZrBz+ NbBz+ MoBz+ TcBz
+
YBz
+
+
+
RuBz RhBz PdBz AgBz+ CdBz+
0.6
0.4
0.2
NA
0.0
1.0
0.8
+
+
+
HfBz TaBz
LaBz
+
+
+
WBz ReBz OsBz
+
IrBz
+
PtBz
NR
NR
+
HgBz
AuBz
+
0.6
0.4
0.2
NA
0.0
O2 addition
MC6H6+ + O2  M+ + (C6H6O2)
----------------------------------------C6H6 + O2  (C6H6O2)
addition/dehydration
O atom transfer
metal abstraction
O +O
benzene abstraction
ligand switching
acetylene elimination
not available or non-reaction
DH = 62.5±2.5 kcal mol-1
O
O
DH = 29.5±0.1kcal mol-1
+O
DH = 16.8±0.3 kcal mol-1
OH
O
O
(M = Fe, Cr, Co)
DH = 14.4±0.1 kcal mol-1
+ O2
O
O
+ H2
CHO
CHO
Caraiman & Bohme
J. Phys. Chem. A 2002, 106,
9705-17.
DH = -44.8±1.1 kcal mol-1
DH = -52.4±0.1 kcal mol-1
C O + H2O
DH = -52.6±1.1 kcal mol-1
HO
OH
DH = -84.8±1.1 kcal mol-1
catechol
C602+ + H  C60H2+ + h
C60H2+ + H  C602+ + H2
-67 kcal mol-1
-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
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 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).
“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
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-
“Molecular Docks”
C60
2+
+ 2 HC3N  C60 + c-(HC3N)2
+•
+
+•
Milburn et al,
JPC A 103 (1999) 7528.
Desirable Attributes:
+
 Provide atomic site (e.g. C)
+ C C CH
N
+
+
+
+
+
N C C CH
HC C C N
N
H
C
+
C C
· +
+•
C C
H
C
N
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.
Isomers of (HC3N)2+•
At B3LYP/6-31+G(d) (top numbers)
and B3LYP/6-311++G-(2df,p) (bottom numbers)
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
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
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
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.