Water network-mediated, electron induced
proton transfer in anionic [C5H5N·(H2O)n]¯
clusters: Size-dependent formation of the
pyridinium radical for n ≥ 3
Andrew F. DeBlase, Conrad Wolke, Gary H. Weddle, Kaye A.
Archer, Kenneth D. Jordan, John T. Kelly, Gregory S.
Tschumper, Nathan I. Hammer, and Mark A. Johnson
International Symposium on Molecular Spectroscopy
June 24, 2015
Proton Transfer Relays in CO2 Reduction
Pyridine catalyzes reduction of CO2 to transportable fuels (i.e. formic acid)
Bocarsly J. Am. Chem. Soc. 2008.
Bocarsly J. Am. Chem. Soc. 2011
CO2 does bind to Py in the gas phase:
Py•
C-N stretch at 1283 cm-1
Kamrath J. Am. Chem. Soc. 2010
Simulations show water networks play a role in stabilizing pyridinium radical
Py•
Musgrave J. Am. Chem. Soc. 2012
Experimental evidence for stabilization of pyridine radical by water network?
Introducing the Hydrated Electron: A Powerful
Reducing Agent in Cluster Chemistry
How do small H2O
clusters bind an e-?
Hammer, et al. Science 2004
e.g. (H2O)n¯ + CH3CN → OH¯∙(H2O)n-m-1 + m H2O + CH3CHN∙
Beyer, M. K., et al. Angew. Chem. Int. Ed. 2003, 42, 5516.
Can we use the hydrated electron to reduce Py to PyH(0)?
Py + (H2O)n¯ → Py·(H2O)n¯ → PyH·(H2O)n-1·OH¯
The Jet Source
Wiley- Pulsed
McLaren Valve
TOF
Ion
Optics
Reflectron
A+∙Arn + hν → A+∙Arn-m + m Ar
hn
2m Flight Tube
kIVR
kevap
Electron
Gun
Nd:YAG
MCP
Detector
OPO/OPA
3 × 103 Torr
10-5 Torr
e-
Ar
Solenoid
60 psi Ar with trace Py and H2O vapors
Py·(H2O)n Mass Spectrum
n=2
[Py∙(H2O)n]¯
[Py∙(H2O)n]¯∙Ar
3
4
5
6
3
7
4
8
5
6
Relative Abundance
Where is n = 2?
100
120
140
160
180
m/z
200
220
Previous Explanation for Onset at n = 3
Py·(H2O)n
[Py·(H2O)n]¯
Potential Energy
n=2
Δ𝐸 > 0
Δ𝐸 < 0
n=3
Rearrangement Coordinate
Desfrancois, et al. Electron. Spectrosc. 2000
Velocity Map Imaging Photoelecton Spectrum
Py·(H2O)3¯
Photoelectron Yield
E
0.00
0.50
1.00
1.50
2.00
Electron Binding Energy (eV)
· Peak at 1.53 eV implies valence electron
· Breadth implies VDE >> AEA
· Not resolved for structural determination
More Complicated Potential Energy Surface
VDE
Hydration Study
[Py∙(H2O)n]¯
𝜈CH
Photoelectrons
free
𝜈OH
𝜈𝛾 𝜈
𝛽
Predissociation Yield
n = 3
𝜈𝛼
n = 4
𝑏
𝜈HOH
n = 5
800
1200
1600
2000
2400
2800
Photon Energy (cm-1)
3200
3600
Experiment and Theory
PyH∙(H2O)n-1∙OH¯
Calculated Intensity / Predissociation Yield
AD
Py
DD
AD
DD
Bend
Perfect
agreement???
CH
n = 5
× 10
M06-2X/6-31+G**
800
1200
1600
2000
×3
NH
AAD
OH¯ bound
2400
2800
Photon Energy (cm-1)
× 30
2nd Shell
3200
3600
AD
free
AD
AAD
Prediss. Yield
Comparison to Model Compounds
HOH bending
PyH∙(H2O)4∙OH¯
𝝂𝟐𝟑 :
𝝂𝟐𝟏 :
Relative Intensity
PyH∙
(In a solid p-H2
matrix)
𝜈23
𝝂𝟐𝟎 :
𝝂𝟐𝟏 :
𝝂𝟒 :
Py
𝜈20 /𝜈4
𝜈21
(FTIR of vapor)
1000
Golec, et al.
J. Phys. Chem. A 2013
𝜈21
1200
1400
Photon Energy (cm-1)
1600
NIST
chemistry
webbook
1800
Acknowledgements
Johnson Lab (Yale)
Zwier Lab (Purdue)
McLuckey Lab (Purdue)
Theory: Ken Jordan (U Pitt),
Nathan Hammer (Ole Miss)
• Funding Agencies: DOE
•
•
•
•
Extra Slides
Photoelectron Spectroscopy
Continuum
NO¯ Photoelectron Spectrum
EKE
A
hνpump
EBE
1.0
1.5
2.0
Electron Kinetic Energy (eV)
Ahνpump = EBE + EKE
2.5
Velocity Map Imaging (VMI)
CCD Camera
Phosphor
NO¯ Image
r
MCP Back
MCP Front
E
r
Flight Tube
μ-Metal
eExtractor (+)
Ion Packet
Ground
Repeller (-)
hνpump
More Complicated Potential Energy Surface
PyH·(H2O)2·OH¯
Potential Energy
VDE
Py·(H2O)3
v=1
Py¯·(H2O)3
X
𝜈OH
AEA
v=0
VDE = 1.66 eV
VDE = 0.75 eV
Rearrangement Coordinate
(B3LYP/aug-cc-pVTZ)
Multiple Isomers?
AD2
AD2
DD
AD1
4.i 0.00 meV
DD
AD1
4.ii 22.4 meV
D3
AD2
D2
AD1
D1
4.iii 60.1 meV
4.iv 64.7 meV
DD
AD1
AD2
4.v 93.6 meV
DD
IR-IR Double Resonance
Laser 1:
v=1
Laser 2:
v=0
Wiley- Pulsed
McLaren Valve
TOF
Reacceleration
Ion
Optics
Photofragment signal
from laser 2 dips when
laser 1 is on resonance
with blue isomer
Reflectron
2m Flight Tube
Electron
Gun
Nd:YAG
MCP
Detector
OPO/OPA
Scanning
Nd:YAG
OPO/OPA
Fixed on Resonace
Hole-burn
Depletion
*
Calc. Intensity
Predissociation
Yield
Probe
*
s
𝜈
a
DD
𝜈 DD
AD2
DD
free
AD1
𝜈 AD
D3
D2
free
𝜈 D2
D1
3450
3500
3550
3600
Photon Energy
3650
(cm-1)
3700
free
free
𝜈 D1 / 𝜈 D3
3750