Three-Dimensional Water Networks Solvating an Excess Positive Charge:
New Insights into the Molecular Physics of Ion Hydration
Conrad T. Wolke
Johnson Group
June 24, 2015
International Symposium on Molecular Spectroscopy
Microhydration of Cs+(H2O)20
AAD
Pentagonal
Dodecahedron
AD
B3LYP/
6-31+G**
Bound OH
stretches
Free OH
stretch
 Cs+(H2O)20 is a “Magic” cluster
 Predict structure from MS (Castleman, 1991)
 Identify structure by the band pattern of free
OH stretch (Williams, 2013)
2800
3200
Photon Energy
3600
(cm-1)
Cooper et al., JPCA, 117, 6571 (2013)
Selinger et al., JPC, 95, 8442 (1991)
Tandem Time of Flight Mass Spectrometer
Temperature
Controlled
Ion Trap
WileyMcLaren
TOF
Turning
Quad
Reflectron
Ion
Optics
Flight Tube
Nd:YAG
RF-Ion
Guides
MCP
OPO/OPA
Tunable IR
600-4500 cm-1
Wavemeter
Dry Air
1st Skimmer
ESI
Capillary
P
mM
Solution
ESI Needle
Pressure
Diff. Stage
1st
2-4 kV
H2O/D2O
Infrared Spectrum of Cs+(H2O)20
Norm. Int. (a.u.)
Cs+(H2O)20
440
460
480
500
520
540
Calc. Int.
Mass to Charge Ratio (amu/e)
Pred. Yield (a.u.)
 Using D2 messenger tagging to acquire complete
IR predissociation spectrum of cold Cs+ hydrates
from 400 to 3800 cm-1
400
B3LYP/
6-31++G**
Knut Asmis
(Free Electron Laser)
Librations
800
1200
H2O
bend
1600
OH
stretches
2000
2400
2800
3200
3600
Photon Energy (cm-1)
Cooper et al., JPCA, 117, 6571 (2013)
Fournier et al., PNAS, 111, 18132 (2014)
Effects of Deuteration: Cs+(D2O)20
D2 Predissociation Yield (a.u.)
2900
3100
3300
3500
3700
3900
Cs+(H2O)20
 IR Bands of the H-bonded network still
featureless
Cs+(D
 Deuteration causes the expected global
red-shift of the IR spectrum
2O)20
 Continuum resolves into distinct bands
2100
2300
2500
Photon Energy (cm-1)
2700
2900
D2 Pred. Yield / Calc. Intensity (a.u.)
Refine Harmonic Calculations: Cs+(D2O)20
 IR Bands of the H-bonded network still
featureless
Cs+(D
 Deuteration causes the expected global
red-shift of the IR spectrum
2O)20
 Continuum resolves into distinct bands
2100
2300
2500
Photon Energy (cm-1)
B3LYP/6-31++G**
2700
 Use all IR features to match experiment
with calculation
2900
Schulz et al., CPC, 18, 98 (2002)
Refine Harmonic Calculations: Cs+(D2O)20
D2 Pred. Yield / Calc. Intensity (a.u.)
Bound
AAD
ADD1
ADD2
ADD3
asym
sym
Free
AAD
 One free OH stretch from AAD type water
•
Cs+(D2O)20
2100
2300
H-Bond acceptor (A) and donor (D)
 Asymmetric bound OH stretches of ADD
type waters
2500
2700
 Corresponding bound AAD OH stretch
2900 and symmetric ADD stretches
Photon Energy (cm-1)
B3LYP/6-31++G**
Schulz et al., CPC, 18, 98 (2002)
Refine Harmonic Calculations: Cs+(D2O)20
D2 Pred. Yield / Calc. Intensity (a.u.)
Bound
AAD
ADD1
ADD2
ADD3
asym
sym
Cs+(D
2100
Free
AAD
Can we assign H-bonded OH
stretches to individual types of
water molecules?
2O)20
2300
2500
2700
2900
Photon Energy (cm-1)
B3LYP/6-31++G**
Schulz et al., CPC, 18, 98 (2002)
Cs+(H2O)6 – Models for Solvation Mechanism
D2 Pred. Yield / Calc. Intensity (a.u.)
MP2/aug-cc-pVDZ
𝝂𝑺𝒊 = 𝝊𝒊 ∙ 𝐞𝐱𝐩 −𝜶𝝊𝒊
James Lisy
UIUC
Cs+(H2O)6
 Unbiased reproduction of IR spectra
• No Scaling
CCSD(T)/aug-cc-pVDZ
MP2/aug-cc-pVTZ (VPT2)
Sotiris S.
Xantheas
PNNL
3200
3300
3400
3500
3600
3700
 Exact mapping of the PES
• Ion – Water
• Water – Water
3800
3900
4000
Photon Energy (cm-1)
Kolaski et al., JCP, 126, 074302 (2007)
Assignment of Local Mode Patterns
𝝊𝒂
𝒇
𝒇
𝝂𝟏
𝝂𝟐
Single
Donor
Cyclic
Core
𝝂𝒃𝟏
𝝊𝒔
𝝊𝒔
D2 Pred. Yield / Calc. Int. (a.u.)
𝝂𝒃𝟏,𝟐
𝝂𝒃𝟐
𝒇
𝝂𝟏,𝟐
𝝊𝒂
CCSD(T)/aug-cc-pVDZ
MP2/aug-cc-pVTZ (VPT2)
𝝂𝒃𝟏,𝟐
𝝊𝒔
3200
3300
3400
3500
𝒇
𝝂𝟏,𝟐
3600
Photon Energy (cm-1)
𝝊𝒂
3700
Can we isolate a single H2O to
prove the band assignment?
3800
Isotopic Labeling Scheme for H-Bonded Networks
Temperature
Controlled
Ion Trap
WileyMcLaren
TOF
Turning
Quad
Reflectron
Ion
Optics
Flight Tube
Nd:YAG
RF-Ion
Guides
MCP
OPO/OPA
Tunable IR
600-4500 cm-1
Wavemeter
Dry Air
1st Skimmer
ESI
Cs+(D2O)Capillary
n + H2Ovap
+
Cs (D2O)n-m(H2O)m
P
ESI Needle
Pressure
Diff. Stage
1st
2-4 kV
D2O
mM
Solution
Isotopic Labeling of Cs+(D2O)n-m(H2O)m
IR Spectroscopic Evidence:
Does H2O stay intact?
D2 O
H2O : D2O →
25% H2O
50% HDO
25% D2O
MS Evidence:
5
Relative Intensity (a.u.)
6
Cs+(D2O)5(H2O)
HOH Bending
D2 Pred. Yield (a.u.)
Liquid phase:
HOD
Bend
H2 O
7
Cs+(D2O)n
1100
H2O
exchange
1200
1300
1400
1500
1600
Photon Energy (cm-1)
 Mass Spec spaced by 2 amu/Z
 No HOD bending mode
 H2O stays intact
230
240
250
260
Mass to Charge (amu/e)
270
1700
Spectral Manifestation of Cs+(D2O)5(H2O)
D2 Predissociation Yield (a.u.)
Cs+(D2O)5(H2O)
 Infrared spectrum of the isotopically
labeled complex stays intact
15cm-1
 Each H2O adds its 2 individual modes
 All 6 position equally populated
 FWHM of OH stretch bands are reduced
Cs+(H
 Evidence for minor vibrational
excitonic coupling
2O)6
27cm-1
Can we isolate modes from
individual H2O molecules?
3400
3500
Photon Energy
3600
(cm-1)
3700
Isotopomer Specific IR-IR Double Resonance
Temperature
Controlled
Ion Trap
WileyMcLaren
TOF
Turning
Quad
Reflectron
Ion
Optics
Coaxial
TOF
Ion
Optics
Reflectron
Flight Tube
MCP
Nd:YAG
MCP
OPO/OPA
Tunable IR
600-4500 cm-1
Wavemeter
Nd:YAG
ESI
Cs+(D2O)n + H2Ovap
Cs+(D2O)n-m(H2O)m
OPO/OPA
RF-Ion
Guides
Isotopomer Specific IR-IR Double Resonance
Temperature
Controlled
Ion Trap
WileyMcLaren
TOF
Turning
Quad
Ion
Optics
Coaxial
TOF
Ion
Optics
Reflectron
Flight Tube
MCP
Nd:YAG
MCP
OPO/OPA
Tunable IR
600-4500 cm-1
Wavemeter
Nd:YAG
ESI
Cs+(D2O)n + H2Ovap
Cs+(D2O)n-m(H2O)m
OPO/OPA
RF-Ion
Guides
𝒇
𝝂𝟏,𝟐
Single
Donor
𝝊𝒔
𝝂𝒃𝟏,𝟐
𝝊𝒂
𝒇
𝝂𝟏,𝟐
IR2MS3 Signal
𝝊𝒂
N2 Pred. Yield (a.u.)
IR2MS3 Signal
Isotopomer Specific IR Spectra of Cs+(H2O)(D2O)5
Cyclic
Core
3400
3500
3600
Photon Energy
(cm-1)
3700
CIVP Spectrum
I–(H2O)(D2O) – Isotopomer Specific IR Spectra
D
D
TTrap = 10 K
A
B
A
C
C
IR2MS3 Dip Signal
B
MP2/aug-cc-pVDZ(-PP)
3200
3300
3400
3500
Photon Energy (cm-1)
3600
3700
CIVP Spectrum
I–(H2O)(D2O) – Isotopomer Specific IR Spectra
D
C D
TTrap = 25 K
B
A
C
A
IR2MS3 Dip Signal
B
MP2/aug-cc-pVDZ(-PP)
3200
3300
3400
3500
Photon Energy (cm-1)
3600
3700
Conclusions
 Trace Isotope Scheme in the gas-phase
Cs+(D2O)20
allows labeling of an intact H2O
 Spectral Isolation of the two OH
stretching modes originating from a
2100
2300
2500
2700
2900
Photon Energy (cm-1)
single H2O molecule
 Deuteration of large clathrate alkali
Cs+(D2O)5(H2O)
hydrates resolves distinct patterns in the
H-bonded water stretch continuum
 Vibrational Spectroscopy to unravel
dynamical behavior in H-Bonded Networks
Acknowledgments
Johnson Group
Joseph A. Fournier
Olga Gorlova
Stephanie M. Craig
Joanna K. Denton
Joseph W. DePalma
Chinh H. Duong
Patrick J. Kelleher
Fabian S. Menges
Gary H. Weddle
Mark A. Johnson
PNNL
Evangelos Miliordos
Sotiris S. Xantheas
Temperature Dependence of I‒(H2O)2
300
Trap Temperature (K)
250
200
150
100
50
17
3200
3300
3400
3500
Photon Energy (cm-1)
3600
3700
Molecular Dynamics of I‒(H2O)2
Francesco Paesani, UCSD
Assignment of Local Mode Patterns
𝒇
𝒇
IR2MS3 Dip Signal
𝝂𝟏
𝝂𝟐
Cyclic
Core
𝝂𝒃𝟏
𝝊𝒔
D2 Pred. Yield / Calc. Int. (a.u.)
𝝂𝒃𝟏,𝟐
𝝂𝒃𝟐
𝒇
𝝂𝟏,𝟐
𝝊𝒂
𝝊𝒂
𝝊𝒔
3200
3300
3400
Single
Donor
CCSD(T)/aug-cc-pVDZ
MP2/aug-cc-pVTZ
(anharmonic)
𝝂𝒃𝟏,𝟐
3500
𝒇
𝝂𝟏,𝟐
3600
Photon Energy (cm-1)
𝝊𝒂
3700
𝝊𝒔
3800
Conclusions
1. Precise Model for Ion solvation
 Exact Predictions for Ion-Water and Water-Water interaction
2. Spectroscopic Isolation of a single isotopically labeled water molecule
 Infrared Transitions
 Chemical Environment
Access to:
 Dynamics
 Phase Transitions of
finite size systems
D2 Predissociation Yield (a.u.)
600
Cs+(H2O)20
Cs+(D2O)20
1000
1400
1800
2200
2600
Photon Energy (cm-1)
3000
3400
3800
D2 Predissociation Yield (a.u.)
600
Cs+(H2O)20
Cs+(D2O)20
1000
1400
1800
2200
2600
Photon Energy (cm-1)
3000
3400
3800
Electronic Structure Calculations
D2 Pred. Yield / Calc. Intensity (a.u.)
+0.947 kcal/mol

MD Calculation produced 1̴ 000
Structures

Refined by DFT yields the vibrational
spectra

Minimum energy structure does not yield
best Fit
Cs+(D2O)20
2100
2300
2500
2700
2900
Photon Energy (cm-1)
B3LYP/6-31++G**
Schulz et al., PCCP, 5, 5021 (2003)
Isotopomer Specific IR Spectra of Cs+(H2O)(D2O)5
N2 Pred. Yield (a.u.)
3718
IR2MS3 Dip Signal (a.u.)
3699
3400
3500
3600
Photon Energy
(cm-1)
3700