long range proton-migration in vuv photoionization of acetone clusters ken-ichi hanaue, yoshiyuki...
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Long Range Proton-Migration in VUV Photoionization of Acetone Clusters
Ken-ichi Hanaue, Yoshiyuki Matsuda, Ayako Yamada, Keisuke Ohta, Naohiko Mikami, and Asuka Fujii
65th International Symposium on Molecular SpectroscopyJune 24, 2010 Ohio State University
Department of Chemistry, Graduate School of Science,Tohoku University, Japan
Cluster cations of protic molecules
IR spectroscopy based on VUV photoionization detection has been applied to cluster cations of protic molecules.
JCP 131, 184304 (2009) PCCP 11, 1279 (2009).
(NH3)2+ (CH3OH)2
+ (CH3COOH)2+
JCP 129, 094306 (2008).
VUV photoionization of protic molecular dimers
intracluster H+- transfer between NH and OH
Can a proton of CH (alkyl group) be transferred?
Roles of solvents in VUV photoionization of solvated clusters?
This study
Understanding of VUV one-photon ionization dynamics of acetone-H2O
○ IR spectroscopy based on VUV photoionization detection of neutral and cationic clusters.
○ Reaction route search with the GRRM (Global Reaction Route Mapping) method
?
VUV photoionization
acetone-H2O
acetone: aprotic molecule
neutral cation
Experiment and calculation
IR spectroscopy of neutral clusters IR spectroscopy of cluster cations
ion signal
IRVUV
S0
IE
dissociationt
V’
IRV’
S0
IE
dissociation
ion signalt
VUV
By changing the relative delaytime between of the IR and VUVpulses, IR spectroscopy of both neutral (precursor) and cationic (product) clusters in the VUV photoionization can be carried out.
IR spectroscopy based on VUV (118 nm) photoionization detection
Experiment
CalculationGRRM (Global Reaction Route Mapping) method (Maeda & Ohno, 2004)
search of reaction routes following photoionization
2600 2800 3000 3200 3400 3600 3800
IR spectra of neutral acetone and acetone-Ar cluster cation
2800 3000 3200 3400 3600 Wavenumber / cm-1
Wavenumber / cm-1
acetone
acetone+-Ar
Scaled by 0.931MP2/6-31++G**
MP2/6-31++G**
Scaled by 0.931
IR-VUV-PIS
IR
VUV
IE
S0
V’
ion signal
VUV @ 118 nm
VUV @ 128 nmneutral
cation
OH
keto16.2 kcal/mol
enol0 kcal/mol
neutral
cation
acetone-H2O
(acetone-H2O)+
2800 3000 3200 3400 3600
Wavenumber / cm-1
2600 2800 3000 3200 3400 3600 3800Wavenumber / cm-1
H-bonded free OH
low IR power
CH
OH
31H-bonded OH
IR spectra of acetone-H2O and (acetone-H2O)+
MP2/6-31++G** scaled by 0.94
scaled by 0.948MP2/6-31++G**
cyclic-type
the alkyl proton migrates !
118 nm photo-ionization detection
118 nm photoionization
two possible mechanisms
photo-ionization
proton-relay
catch & release
Proton migration mechanism
enol form with the proton migration
cation
keto form
VUV photoionzation
proton-migration induced by photoionization
neutral
DD
DD
neutral acetone-D2O
acetone-D2O cation
2600 2800 3000 3200 3400 3600 3800Wavenumber / cm-1
2800 3000 3200 3400 3600 3800Wavenumber / cm-1
free OD
CH
H-bonded OH
no free OH
proton-migration
catch & release
IR spectra of neutral and cationic acetone-D2O clusters
catch & release
Proton-migration induced by photoionization
Proton-migration in ionization process
Calculated isomerization path in photoionization with the GRRM methodPBE1PBE/6-311+G(2d,2p)
catalytic action of the water molecule
enol Ienol II
Intracluster proton-transfer from CH occurs upon the photoionization.
IR spectroscopy based on VUV photoionization detection and reaction route search with the GRRM method were carried out to study VUV one-photon ionization dynamics of the acetone-water cluster.
enol type cationneutral proton-migration
Summary
catch & release
VUV
The water molecule acts as the “catch & release” catalyst in the proton-migration.
acetone-water
ionization
apparatus
pulsedvalve
rare gascell
tim e of flightm ass spectrom eter
MCPdetectorVUV
IR (DFG)
IR (OPO)1st. Q-m ass 2nd. Q-m ass
octopoleion guide
channeltrondetector
rare gascell
VUV
fragment ion
Ion
Inte
nsity
IR frequency
parent ion
Ion
Inte
nsity
spectroscopy of neutral and cations
spectroscopy of cations
Setup ITOF & DFG
Setup IITandem Q-mass & IR-OPO
dip spectrum
enhancement spectrum
IR frequency
Mass spectrum of photoionization @118 nm
12 13 14 15 TOF / s
Mass spectrum of acetone-H2O @118 nm
(acetone-H2O)+
(acetone)+
no higher clusters
2600 2800 3000 3200 3400 3600Wavenumber / cm-1 Scaled by 0.948 MP2/6-31++G**
1 3
free OH
CHx10
x10
x10
H-bonded OH
CH H-bonded OH
CH
CH
CH
13
1 3
13
H-bonded OH
absorption
(a)
(b)
(c)
(d)
(e)
(a) H+-migrated 0 kcal/mol
(b) H+-migrated II 0.7 kcal/mol
(c) Charge-shared I 26.4 kcal/mol
(d) Charge-shared II 29.2 kcal/mol
(e) H-transferred 33.2 kcal/mol
IR spectrum of acetone-water cluster cation
IRPDS-VUV-PI@118 nm