EXPLORING SOLVENT SHAPE AND FUNCTION USING MASS-
AND ISOMER-SELECTIVE VIBRATIONAL SPECTROSCOPY
Special thanks to Tom, Anne and Terry
Outline
Ar-cluster mediated trapping of reaction intermediates as size-selected cluster ions
Reaction motifs in water splitting Characterization by vibrational predissociation spectroscopy Network-dependent activation of water in covalent bond
formation: NO+ ·(H2O)n
Instrument modifications to access electrosprayed ions Ring closure mechanics of dodecanoic acid conjugate anions
Yale
Rachael Relph
Mike Kamrath
Chris Leavitt
Tim Guasco
Arron Wolk
Krissy Breen
Helen Gerardi
Prof. Gary Weddle (Fairfield)
AFRL Cambridge
Dr. A.A. Viggiano
Univ. of Pittsburgh
Prof. Ken Jordan
Dr. Daniel Schofield
Ohio State
Prof. Anne McCoy
Yale
Prof. John Tully
Dr. Ryan Steele
Experiment Theory
Eldon Ferguson
RachaelMike
Ben, PhD 2010, Now with
Schwartz, UCLA
Gary Tim
Krissy HelenThursday talks
Yale Solar Group-small biomimetic catalysts
O H
CO2-
N
N
N
MnO
OMn
N
N
N
L
L-O2C
-O2C
-O2CCO2-
CO2-
Oxidn.LMnV=O H2O
O2 + 2H+
3-
IV IVor
LMnIV-O•
MnO2Mn OH2III -e-,-H+
Mn OHIV -e-,-H+
Mn O• Mn OH2O,-H+
IV III
(1)
(2)Mn(OH)2Mn
O2
H2O, -e-
MnO
OMn
N
N
IV IVOL
N
N N
NO
SO3-
-SO42-
thermalMn
O
OMn
N
N
IV ? OL
N
N N
N
Our known compound
oxo or oxyl?
H2O,-H+
MnO
OMn
N
N
IV IV OOHL
N
N N
N
observable?
(3)
(4)Mn
O
OMn
N
N
IV IVOL
N
N N
N MnO
OMn
N
N
IV IV LN
N N
N
Ar+
-Mn2O2(terpy)2LIV
IV
H+
III II
“Harnessing the power of photosynthesis to make green fuel”
Making the O-O bond
• Very high oxidation states put water in unusual chemical environment
• Cooperative, complex reaction coordinate!
• Proton removed and O-O bond forms
OVIr
OHIVIr
-H+/-eˉ
+
OHH
- +
OHH
Large shifts in excess proton-
based vibrations:“Frozen
snapshots” of diffuse ir signature
of free proton in dilute acids
H+(H2O)n∙Ar spectra
Spectral signatures of mobile protons
Headrick, M. A. Duncan,MAJ,
Science, 308, 1765 (2005),
N=O+
O
H
H
N=O
O
H
H
solvated nitric oxide solvated nitrosonium
clusters provide a controlled environment to titrate the extent of proton transfer
-e-
N=O
OH
pKa drop
solvation in liquid water leads to formation of
acid
low dielectric allows onlypartial release of proton
oxidation
N=O
O
H
HB: +
Getting started…2009
Proton-coupled covalent bond formation
proton transfer
H
+O H
H
NO+(H2O)n ∙ Arp + H2O → NO+
(H2O)n+1 ∙ Arq + (p-q) Ar
Cryogenic Ion Chemistry
Rational preparation of reaction intermediates using Ar cluster-mediated condensation
NO+(H2O)n
H2OHONO + H+(H2O)n
NO+(H2O)n + H2O → HONO + H+(H2O)n
Atmo reaction, Ferguson ‘71Okumura, ‘93
Reaction coordinate is solvent shape
Application to the nitrosonium hydrates
1 keVelectron
beam
NO+ ∙ Arm + H2O → NO+(H2O) ∙ Arp + (m-p) Ar
NO+(H2O) ∙ Arp + H2O → NO+(H2O)2 ∙ Arq + (p-q) Ar
H2O
kV
NO/Ar
time of flight
NO+ (H2O)2Ar
NO+ (H2O)4Ar
NO+ (H2O)3Ar
Ar12+
NO+ Ar9
1 keVelectron
beam
T.O.F.
Nd:YAG pumped OPO/OPA
600 – 4500 cm-1
reflectron
MCP detector
H2O
kV
NO/Ar
NO+(H2O)n ∙ Arp + h → NO+(H2O)n ∙ Arq + (p-q) Ar
Structural characterization by Ar tagged ir spectra
increasing charge on solute
1400 1800 2200 2600 3000 3400 3800
Photon Energy, cm-1
NO+HONO
Distinct spectral regions for solute and solvent response
Solute response
ReactantProduct
H9O4+ Free OH
increasing charge on
solvent
Reactant
Solvent response
Product
NO+(H2O)n + H2O → HONO + H+(H2O)n
increasing charge on
solute
1400 1800 2200 2600 3000 3400 3800
Photon Energy, cm-1
H9O4+NO+
Pre
dis
soci
ati
on
Yie
ldbend
Free OHHONO
increasing charge on
solventNO+ · (H2O)1
NO+ · (H2O)2
ba
gNO+ · (H2O)3
HONONO+ · (H2O)4
Reaction complete
Isomers?
Argon-solvated Isomer IArgon-solvated Isomer IIIsomer I or II fragment induced by pump laserIsomer II fragment induced by probe laser
Sig
nal
Time of Flight, ms
ion beam
pulsedvalve
1 keV electron gun
reflectron
hnpump hnprobe
coaxial TOF
drifttube
MCP iondetector MCP ion
detector
reflectron
Nd:YAG pumped OPO/OPA
600 – 4500 cm-1
±1.5 keV
Nd:YAG pumped OPO/OPA
600 – 4500 cm-1
Isomer-selective Spectroscopy: Development of MS3 IR2 technique in 2008
1900 2100
b
a
g
2300
Disentangle high energy bands in DR scanning mode
2600 3000 3400 3800 4200
Pre
dis
socia
tion
Yie
ld
Photon Energy, cm-1
Probe
Probe
3640 3680 3720 3760
Ion
Dip
Sig
nal
Photon Energy, cm-1
2600 3000 3400 3800
3600 3800P
redi
ssoc
iatio
n Y
ield
2400 2800 3200 3600 4000
probe *
probe ‡ *
‡
A few bands still hopelessly overlapped!
Deconvolute using covariance behavior
1900 2100
b
a
g
2300
Three embedded patterns
2600 3000 3400 3800 4200
Pre
dis
socia
tion
Yie
ld
Photon Energy, cm-1
Probe
Calculated isomers of NO+·(H2O)3
DE=2.4 (1.9)DE=0.0 (0.0)
DE=4.3 (4.0)DE=2.6 (2.2)
DE=3.4 (1.2)
MP2/aug‑cc‑pVTZ
kcal/mol(ZPE corrected)
Three observed by hole burning
increasing charge on
solute
1400 1800 2200 2600 3000 3400 3800
Photon Energy, cm-1
H9O4+NO+
b
Pre
dis
soci
ati
on
Yie
ld
bend
Free OH
a
HONO
g
increasing charge on solvent
3-a3-b3-g
Strong correlation between solvent and solute response to changing solvent coordinate
Arrangement stabilizes charge on shared protons
γ motif with two waters in second solvation shell most reactive
+
Hydrated NO+
Electron flow
OH
N
H
O
3-a 3-g3-b
Intra-cluster charge-transfer (neutralization of NO+) strongly dependent on shape of attached
water network
Electron density difference contours upon ion hydration
(fixed water network at product geometry)
Explicit, molecular level solvent coordinate for reaction
Relph et al., Science, January 2010
parent ion
800700600500400300Mass (amu)
mass = 483
“Cryogenic ion chemistry” with water splitting catalysts?
Cryogenic Ion Chemistry
Rational preparation of reaction intermediates using Ar cluster-mediated condensation
• Standard approach: Ar tagging in supersonic expansion
– Argon Heat of Evaporation: 500 cm-1 – Only works on small systems where vibrational degrees of
freedom can be quenched by Ar during the expansion
Challenge: Vibrational cooling of large systems
X·Arn X·Arm + Arn-m
NO+ · (H2O)3 · 7 Ar NO+ · (H2O)3 · Ar + 6 Ar
3N – 6 = 27 ~ 9 Ar atoms
3N – 6 = 135~ 50 Ar atoms
Tagging with H2
Xuebin Wang at PNNL
{ONLY the dianions tag with H2 }
Thank You Lai-Sheng Wang and Xuebin
Wang!
-O2C(CH2)12CO2- n H2
RF only quadrupoles
Heated copper block
1st skimmer
2nd skimmer
aperture
Octopole ion guide
90° quadrupoleion bender
H2/He filled 3-D quadrupole ion trap with temerature control to 8 K
Octopole ion guidewith Einzel stack
Electrospray needle
Instrument construction2009-2010
Thanks: Tom RizzoScott AndersonDieter GerlichXuebin and Lai-Sheng
He/H2 buffer gas
72 74 76 78
Time of Flight (ms)
30 ms
50 ms
40 ms
20 ms
0 ms
doubly-chargedparent
RF
RF
Pulsedvalve
Ions in Ions out
Paul Trap
H2 adduct formation in a 3-D Paul trap:Pulse cooling gas and delay extraction after pump out
10 ms gas pulse
Delay to extraction
10 K
Starting with a known standard
–O2C(CH2)6CO2– · Kr
1200 1600 2000 2800 3200 3600 4000
CO2 sym. stretch
H2 predissociation spectroscopyOkumura & Lee 1990
Photon Energy, cm-1
H2 stretch
B3LYP/6-311++g(d,p)Calc
ula
ted Inte
nsi
tyH
2 P
redis
s. Y
ield
–O2C(CH2)10CO2– · (H2)10 + hν → –O2C(CH2)10CO2
–· (H2)5 + 5 H2
CH stretches
Dodecanedioic acidO
OH
O
HO
C-O stretches
H2 attachment site
1200 1600 2000 2800 3200 3600 4000
Photon Energy, cm-1
H2 P
redis
s. Y
ield
Calc
ula
ted Inte
nsi
ty
B3LYP/6-311++g(d,p)
CH stretches
H2 stretchCO2 sym. stretch
Free H2 CO2 asym. stretch
Packing of H2 molecules
n = 10
Relatively sharp, red-shifted band (by 250 cm-1)Many molecules in first solvent shell?
B3LYP/6-311++G(d,p)
Can fit 8 H2 around each CO2 group
Where the H2 sticks in the di-anion
1200 1600 2000 2800 3200 3600 4000
Photon Energy, cm-1
H2 P
redis
s. Y
ield
Calc
ula
ted Inte
nsi
ty
B3LYP/6-311++g(d,p)
H2 stretchCO2 asym. stretch
CO2 sym. stretch
CH stretches
Where the H2 sticks in the di-anion
1200 1600 2000 2800 3200 3600 4000
Photon Energy, cm-1
H2 P
redis
s. Y
ield
Calc
ula
ted Inte
nsi
ty
B3LYP/6-311++g(d,p)
H2 stretchCO2 asym. stretch
CO2 sym. stretch
CH stretches
Extending H2 tagging to the singly-charged species
[CO2(CH2)10CO2H]-·nH2
T=11 K
224 226 228 230 232 234 236 238 240m/z
n =0 1 2 3 4
72 74 76 78Time of Flight (ms)
n = 14many peaks but only doubly-
charged species tags
1000 1400 1800 2200 2600 3000 3400 3800 4200Pre
dis
soci
ati
on
Yie
ld
Photon Energy, cm-1
Calc
ula
ted Inte
nsi
ty
a)
b)
c) free H2
stretch
free OH
sharedproton
CH stretches
C=O stretches
CH backbone
Missing free OH signals ring formation
C-O bands reveal asymmetrical internal H-bond
C=OBlue shift
C-Ored shiftCO2ˉ bond order
1.5
800 1200 1600 2000 2800 3200 3600 4000
Photon Energy, cm-1
C-O bands reveal asymmetrical internal H-bond
Carboxylate is intact
800 1200 1600 2000 2800 3200 3600 4000
Photon Energy, cm-1
C-O bands reveal asymmetrical internal H-bond
Carbonyl emerges
800 1200 1600 2000 2800 3200 3600 4000
Photon Energy, cm-1
C-O bands reveal asymmetrical internal H-bond
C-OH lost in CH2 background
Going to need a better mass spec
• Current mass spec only has unit mass resolution at 500 AMU
• Photocatalysts have metal centers with multiple isotopes
ex: 191Ir (37%) and 193Ir (63%)
• With doubly charged species loss of a single H2 may be difficult to detect
The next generation: ICR
Delivery date: June 7
Etienne Garand, PhD NeumarkDelivery date: July 1.
Resolution 450,00016 cm bore (77 K cell, Williams, Berkeley)
• Observed explicit solvent coordinates facilitating covalent N-O bond formation
• Implemented cryogenic ion source into triple-focusing tof mass spec to study photoactive catalysts from the Yale Solar Group
• Next phase of construction: ICR
Conclusions
Thank you