1. Vibrational Signatures of Solvent-Mediated Core Ion Deformation in Size-Selected [MgSO4Mg(H2O)n=4-11]2+ Clusters
Patrick Kelleher, Joseph DePalma, Christopher Johnson,
Joseph Fournier, and Mark Johnson
70th International Symposium on Molecular Spectroscopy
June 22, 2015

2. Center for Aerosol Impacts on Climate and the Environment
Mg2+ inhibits production of ClNO2
Allen group, J. Phys. Chem. A, 2013, 117, 13412−13418

3. Center for Aerosol Impacts on Climate and the Environment
[Mg(Palmitate-)(Palmitic)2]+
FT-ICR MS
Mg2+ inhibits production of ClNO2

4. Ternary Salt Complex [MgSO4Mg]2+
D2 tag
+2 m/z
Start simple: MgSO4. Very soluble salt, electrosprays well and readily generates hydrated clusters
How do water molecules bind to a “salt bridge” ternary ion core?

5. Cryogenic Ion Vibrational Predissociation (CIVP) Spectroscopy
A‾ · Tagm + hn → A‾ · Tagn + (m-n) Tag
Generate
Ions and
Condense Tag
Isolate
One Mass
Excite
With Laser
Detect
Fragmentation
and Generate
Spectrum hn
kIVR
kevap a) b) c) d)
mass
mass

6. CIVP Experimental Setup
2-4 kV
Dry Air mM
Solution
1st Skimmer
Capillary
ESI Needle
H2O/D2O P
Pressure
1st Diff. Stage

7. Survey of MgSO4Mg(H2O)n2+ Spectra
asym
(E)
SO4
asym
(B2)
OH Stretch
H2O
bend
Hydrogen Bond νs
νas
n=4
n=5
n=6
D2 Predissociation Yield
n=7
n=8
n=9
n=10
n=11
1000
1200
1400
1600
3000
3200
3400
3600
3800
Photon Energy (cm-1)

8. Survey of MgSO4Mg(H2O)n2+ Spectra
asym
(E)
SO4
asym
(B2)
OH Stretch
H2O
bend
Hydrogen Bond νs
νas
n=4
n=5
n=6
D2 Predissociation Yield
n=7
n=8
n=9
n=10
n=11
1000
1200
1400
1600
3000
3200
3400
3600
3800
Photon Energy (cm-1)

9. Expected Symmetry of Salt Ion Core
SO4 asym
(B2)
Calculated Intensity
Photon Energy (cm-1)
SO4 asymmetric stretch
(triply degenerate F2)
SO2 asym
(doubly degenerate E) θ
O-S-O =
109.5° E
O-S-O =
101° θ B2

10. Observation of Symmetrical Hydration
Calculated Intensity/D2 Predissociation Yield
1000
1200
1400
1600
3400
3500
3600
3700
3800
B3LYP/
G(d,p)
Photon Energy (cm-1)
H2O
bend
SO4
asym νs
νas
SO2
MgSO4Mg(H2O)42+
(2:2) arrangement lies 8.33 kcal/mol and 39.6 kcal/mol lower than (3:1) and (4:0) arrangements, respectively

11. Observation of Symmetrical Hydration
Tag induced splitting
Calculated Intensity/D2 Predissociation Yield
1000
1200
1400
1600
3400
3500
3600
3700
3800
B3LYP/
G(d,p)
Photon Energy (cm-1)
H2O
bend
SO4
asym νs
νas
SO2
MgSO4Mg(H2O)42+
(2:2) arrangement lies 8.33 kcal/mol and 39.6 kcal/mol lower than (3:1) and (4:0) arrangements, respectively

12. Differential Hydration Further Reduces Symmetry
SO2
asym
(E)
SO4
asym
(B2)
2 + 2
H2O
bend
1000
1200
1400
1600
1800
Mg2+
n=4
Mg2+
3 + 2
SO42¯
n=5
3 + 3
D2 Predissociation Yield
n=6
4 + 3
n=7
Photon Energy (cm-1)

13. Bifurcated Motif in n = 4-7 Clustersθ
n = 4
n = 5
n = 7
Solvation of Mg2+ ions weakens the interaction
between the constituents of the ion core

14. Survey of MgSO4Mg(H2O)n2+ Spectra
asym
(E)
SO4
asym
(B2)
OH Stretch
H2O
bend
Hydrogen Bond νs
νas
n=4
n=5
n=6
D2 Predissociation Yield
n=7
n=8
n=9
n=10
n=11
1000
1200
1400
1600
3000
3200
3400
3600
3800
Photon Energy (cm-1)

15. Survey of MgSO4Mg(H2O)n2+ Spectra
asym
(E)
SO4
asym
(B2)
OH Stretch
H2O
bend
Hydrogen Bond νs
νas
n=4
n=5
n=6
D2 Predissociation Yield
n=7
n=8
n=9
n=10
n=11
1000
1200
1400
1600
3000
3200
3400
3600
3800
Photon Energy (cm-1)

16. New Binding Motif: Onset of Hydrogen Bonding
Calculated Intensity/D2 Predissociation Yield
1000
1200
1400
1600
3400
3500
3600
3700
3800
B3LYP/
G(d,p)
Photon Energy (cm-1)
H2O
bend
SO4
asym νs
νas
SO2
MgSO4Mg(H2O)42+
Bifurcated motif dictates the geometry of the n = 4-7 clusters

17. New Binding Motif: Onset of Hydrogen BondingA
n = 9
n = 10
D2 Predissociation Yield
H2O
bend
SO2
asym A B
νas
IHB OH stretch
SO4 νs
n = 8
n = 9
n = 10
1000
1200
1400
1600
3000
3200
3400
3600
3800
Photon Energy (cm-1)

18. Survey of MgSO4Mg(H2O)n2+ Spectra
asym
(E)
SO4
asym
(B2)
OH Stretch
H2O
bend
Hydrogen Bond νs
νas
n=4
n=5
n=6
D2 Predissociation Yield
n=7
n=8
n=9
n=10
n=11
1000
1200
1400
1600
3000
3200
3400
3600
3800
Photon Energy (cm-1)

19. Survey of MgSO4Mg(H2O)n2+ Spectra
asym
(E)
SO4
asym
(B2)
OH Stretch
H2O
bend
Hydrogen Bond νs
νas
n=4
n=5
n=6
D2 Predissociation Yield
n=7
n=8
n=9
n=10
n=11
1000
1200
1400
1600
3000
3200
3400
3600
3800
Photon Energy (cm-1)

20. Solvent Separated Ion Pair
Add a water to the n = 10 cluster?
X-Ray Crystal Structure of MgSO4(H2O)6
Batsanov, Acta Crystallographica C, 2000
Hexahydrite mineral
Calculated Structure of MgSO4Mg(H2O)112+ SSIP
SSIP has never before been observed
in cluster ion spectroscopy!
3.12 kcal/mol above global minimum
structure

21. SSIP vs. Second Hydration Shell Configuration
Free OH
IHB OH stretch νs
νas
IRMPD Spectrum
Solvent Separated Ion Pair
x10
IRMPD/Calculated Intensity νD
Second Hydration Shell
νD-as
νD-s
2700
3000
3300
3600
3900
Wavenumber (cm-1)

22. Acknowledgments Johnson Lab Prof. Mark A. Johnson Prof. Gary H. Weddle
Dr. Fabian Menges
Dr. Joe DePalma
Joseph Fournier
Conrad Wolke
Olga Gorlova
Stephanie Craig
Chinh Duong
Joanna Denton

23. [Mg(Palmitate-)(Palmitic)2]+
What’s next?
Continue to search for the elusive solvent separated ion pair!
Continue CAICE collaboration by incorporate organic acids and alcohols to mimic chemistry taking place at the surface of the ocean
[Mg(Palmitate-)(Palmitic)2]+
FT-ICR MS