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De-Yin Wu, Yan-Li Chen, Zhong-Qun Tian
ISMS71 ---RJ12
Theoretical Study on SERS of Wagging Vibrations of Benzyl Radical Adsorbed
on Silver Electrodes
College of Chemistry and Chemical Engineering
& State Key Laboratory of Physical Chemistry for Solid Surfaces
2016.6.23
Studies on solution/metal electrodes
High detection sensitivity
High Resolution
Energy
Space
Time
2-20 Å
Surface-enhanced Raman spectroscopy:SERS
Surface plasmon resonance
Chemical property
EC-SERS (Metal NPs + Molecule + Light)
KE
Ag AgAg Ag
633 nm laser
SH
H2N
SilverGold
CopperRough
electrode surfaces
Nanostructures
a. 1010 cm-1; d. 1215 cm-1
b. 1036 cm-1; e. 1594 cm-1
c. 3056 cm-1; f. 623 cm-1
Potential-Intensity Profiles dependent on Laser Lines
DY Wu, JF Li, B Ren, ZQ Tian, Chem. Soc. Rev. 2008, 37, 1025
At the open circuit potential At the peak potential of the ring breathing mode
Electrochemical Surface-Enhanced Raman Spectroscopy of Pyridine
Pyridine N-Metal Interaction: Pt > Au, Cu > Ag
DY Wu, JF Li, B Ren, ZQ Tian, Chem. Soc. Rev. 2008, 37, 1025
Electrochemical CV and SERS of Benzyl Chloride on Silver Electrodes
Cyclic voltammetry of PhCH2Cl, 5 mM in 0.1 M TEAP + CH3CN, at a Ag electrode (2 mm diameter) and a scan rate of 0.2 Vs-1.
Potential dependent SERS spectra of PhCH2Cl on Ag electrode, excited by
633 nm
J. Am. Chem. Soc. 2010, 132, 9534-9536.
Computational details
Cluster Model: Molecule-Mn; Mn – Molecule – Mn (M = TM)
DFT: B3LYP, PW91PW91, …
Basis set: LANL2DZ (Ag)/ Optimized structure
6-311+G(d,p)(C,N,H,S) Bonding analysis
Scaled Quantum Mechanics force field method (SQMF)]
Calculations of Raman Intensity:
( )( ) ( )
42 20
2 45 78 45 1 exp
R ii i i
i i B
v vhIcv hcv k T
α γπ
−′ ′= ⋅ +
− −
Non-resonance, pre-resonance, and resonance cases
C
C
C
C
CN
H
H
H
H H
M
M
M M MM
MMM
Y
Z
Metallic Cluster Modeling: Size effect
M = Cu, Ag, Au, TM
Small Large
22
745
+
=
kkk dQ
ddQdS γα
( ) 144
2
~exp1
45
~~2~8
−
−−
−=
Ω
∝
kThc
Sch
ddI
kk
ki
k
kRaman
νννπνπ
σ
M-m
Qi
E M+-m-
hv
SERS Intensity: Raman scattering processes
Raman Intensity:
0 00
13
yyxx zz
Q Q Qαα αα
∂ ∂ ∂′ = + + ∂ ∂ ∂ 22 2 2 22
2
0 0 00 0 000 0
1 62
yy yy yz xyxx xx xzzz zz
Q Q Q Q Q Q Q Q Qα α α αα α αα α
γ ∂ ∂ ∂ ∂ ∂ ∂ ∂∂ ∂ ′ = − + − + − + + + ∂ ∂ ∂ ∂ ∂ ∂ ∂ ∂ ∂
Schrödinger Equation: H = T + V, V=V(R) Vibrational peaks
∑≠
Γ++−
+Γ+−−
=FIK KFKKIK iEE
FKKIiEEFKKI
, 00, ω
µµωµµ
α σρρσσρ
Kramers-Heisenberg-Dirac Dispersion Equation
Qi
E
M-m
M+-m-
SERS Intensity: Resonance Raman Scattering
D. Wu, et al., Spectrochim. Acta A, 2004, 60, 137;J. Chem, Phys. 2005, 122, 094719
( )
2 2
,1 ,
22 1
nn
CEfb v
Q
ρσρ σ
α
α==
∂+ ∂
∑∑~10 - 103
( ) ( ) ( )
( )( ) ( )
( ) ( )
22
1 , 0
2
0
, 1 ,
2 2 1
1
1 /
1exp 02
i i
i
i
ia a app i am ma
i i
i i i i
m n m n app i ii i
I V s M M
edt
e
et it a V G th
λ
λ
ββ β
β β β β
ω ω ω
′−∞
′−
′= ′+
−
′ ′+ − +×
× −Γ + + + +
∫
∑ ∏
D.Y. Wu*, et al., Spectrochim. Acta. A, 2004, 60, 137.
D. Y. Wu*, et al., J. Phys. Chem. C, 2008, 112, 4195.
Experiments
950 1000 1050 1100
% (v1 and v12 resonance)Γv1
= 3 cm-1
Γv12 = 2 cm-1
ΓCT = 1880 cm-1
Wavenumber (cm-1)
Energy matching between photon and the CT state
Charge transfer mechanism of pyridine/Ag
Theory
No CT
sp2 sp3 hybridization
Wagging Vibrations of Amino Group in Adsorbed Aniline
J. Phys. Chem. C, 2011,115, 4174
Aniline Benzyl species
Simulated Raman Spectra of PATP/Ag or Au
J. Phys. Chem. C, 2011,115,4174-4183
J. Phys. Chem. C, 2009,113,18212-182212
p -Aminobenzoic acid at Ag electrode
Aniline/Ag Electrode
Aniline/AgNP
Benzidine/Ag
Wagging Vibrations of Aniline and its derivatives/Ag
Tian, et al, Acta Phys. Chem. Sinica, 1987, 3, 178.Li, et al, Environment Sci. & Tech., 2011, 45,4046Kim, et al., J. Phys. Chem., 1990, 94,7576
Benzyl and Amino Groups Adsorbed on Silver Electrodes
yy
xxzz
zz
xx
yy
Free state
Adsorption
Amino Benzyl radical
S. Tao, et al., J. Phys. Chem. C., 2013, 117, 18891
-0.30
-0.25
-0.20
-0.15
-0.10
-0.05
-1.0 -0.5 0.0 0.5 1.0
LOMO
E(a.
u)
Normal coordinate
HOMO
(A)
sp2
-0.20
-0.15
-0.10
-0.05
0.00
0.05
-1.5 -1.0 -0.5 0.0 0.5 1.0 1.5
LUMO
E(a.
u)
Normal coordinate
HOMO
(B)
sp2
J. Phys. Chem. C, 2013,117,18891
Wagging Vibrations of Aniline and Benzyl/Ag
Three factors:1. Binding strength2. p-π3. sp2-sp3
SERS spectra of Benzyl adsorbed on silver electrodes J. Am. Chem. Soc. 2010, 132, 9534-9536.
Wagging Vibrations of Benzyl/Ag and Aniline/Ag Nanopart.
Summary
(1) Chemical enhancement effect is significantly influenced by charge transfer and chemical binding interaction on metal electrode surfaces.
(2) The p-π conjugation effect, hybridization effect, and the strength of the binding interaction influence on the surface Raman bands of wagging vibrations (Vibrationalfrequency and Raman intensity).
(3) Quantum chemical calculation is helpful to understand the observed phenomena in surface Raman spectra in Electrochemical interfaces. EC-SERS + QC
Acknowledgements:
Collaborators:
Prof. Zhong-Qun Tian (Xiamen University) EC-SERS Expt
Prof. Bin Ren (Xiamen University) EC-SERS Expt
Prof. Zhi-Lin Yang (Xiamen University) SERS-Surface Plasmon
Prof. S. H. Lin (IAMS, Taipei) Molecular Spectroscopy
Students:
Song-Yuan Ding, Xiu-Min Liu, Yi-Fan Huang, Ran Pang, Liu-Bin Zhao, Rong Huang, Xi Jin, Wen-Li Luo, Sha Tao, Li-Juan Yu, Zi-Feng Liu
Fund: NSF of China, Basic Research Project of MOST
D.Y. Wu*, et al., Spectrochim. Acta. A, 2004, 60, 137.
D. Y. Wu*, et al., J. Phys. Chem. C, 2008, 112, 4195.
Experiments
16
950 1000 1050 1100
% (v1 and v12 resonance)Γv1
= 3 cm-1
Γv12 = 2 cm-1
ΓCT = 1880 cm-1
Wavenumber (cm-1)
Theory
Energy matching between photon and charge transfer state
Charge transfer mechanism of pyridine/Ag