INFRARED SPECTROSCOPIC STUDY ON FERMI RESONANCE OF
THE EXCESS PROTON VIBRATION IN BINARY CLUSTERS
Ryunosuke SHISHIDO, Asuka FUJIIDepartment of Chemistry, Graduate School of Science,
Tohoku University, Japan
Jer-Lai KUOInstitute of Atomic and Molecular Sciences,
Academia Sinica, Taipei, Taiwan
June 17,2013MK12
In a protonated binary cluster : [A ・ H+ ・ B]The excess proton location
The magnitude of delocalization
are determined by the difference of the proton affinities
M. A. Johnson et al.,Science 316, 249 (2007)
2
IntroductionM. A. Johnson’s group measured the vibrational spectra of some protonated binary clusters [A ・ H+ ・ B]
The excess proton vibration (O-H+ stretch) frequency goes down as DPA decreases
Dec
reas
ing D
PA
(DPA: PA difference of A and B)
3
This study
◆Does the magnitude of the low-frequency shift of the proton vibration depend only on DPA?
◆Does the real proton motion need a multi- dimensional mode analysis?
Infrared photodissociation spectroscopy
Quantum chemical calculations
N-H+---X systems
4
This study
change of the N-H+ stretching vibration with decrease of DPA
(CH3)3N-H+-X (Protonated trimethylamine(TMA) –X cluster)
X = Ar, N2, CO, C2H2, H2O, CH3OH, C2H5OH, CH3COCH3,C2H5OC2H5, NH3, CH3NH2, and (CH3)3N
Amine-H+-H2OAmine : NH3, CH3NH2, (CH3)2NH, and (CH3)3N
We found the Fermi resonance of the excess proton vibration with overtones of N-H+ bending modes
TMA H+
5
+
massselection
v = 1
hnIR dissociation
massselection
1st-Qmass
2nd-Qmassoctopole ion guide
[TMA-H+-X]
[TMA-H+-X]
[TMA-H+]X
[TMA-H+]
discharge
Infrared photodissociation spectroscopyExperiment
6
IR and simulated spectra of TMA-H+-X
■The N-H+ stretching frequency goes down as DPA between TMA and X decreases
■When the N-H+ stretching frequency gets into around 3000 cm-1 region, complicated Fermi resonance is always seen
Calc. @B3LYP/6-31+G(d), Scaling factor : 0.9736
7
ΔPA dependence of the excess proton vibration frequency
■The frequencies of the excess proton vibrations are low-frequency shifted with DPA decrease
band splitting
8
Comparison between the O-H+ and N-H+ stretches
■The shift of the N-H+ stretching frequency is smaller than that of the O-H+ stretching frequency in this DPA region
The shift of the O-H+ stretching frequency The shift of the N-H+ stretching frequency
Large shift
M. A. Johnson et al.,Science 316, 249 (2007)
Small shift
■Sudden decrease of the N-H+ stretching frequency in homo dimer? ( ~ 500 cm-1 in H3N-H+-NH3)
?
9
DPA change by changing the cluster size of water molecules
■The Fermi resonance changes by changing the cluster size of water molecules
free OH
free OH
free OH
νOH
νOH
N-H+
νOH
νOH
(PA of the water moiety changes)
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DPA changes by changing the amine moiety
■The Fermi resonance changes by the change of the amine moiety
free OH
free OH
free OH
free OH
free NH
free NH
free NH
N-H+
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TMA-H+-X, TMA-H+-(H2O)n, and Amine-H+-H2O
The Fermi resonance is a general phenomenon in the N-H+--X systems at -3000 cm-1 region
The multi-dimensional motion occurs in this region
12
Assignments of the coupling partner withthe N-H+ stretching mode
According to the spectrum of TMA(d9)-H+-H2O,■The coupling partner with the N-H+ stretching vibration is not C-H stretching mode
■The remaining candidate is overtone of the N-H+ bending mode
disappear
13
IR spectra of TMA-H+-H2O & TMA-H+-H2O (Ar tagged)
■All the bands show narrowing through Ar attachment According to the spectrum of TMA-H+-H2O(Ar tagged),
■The Intensity alternation of the peaks is due to the dissociation efficiency of Ar■The prominent peak around 2800 cm-1 is attributed to the major component of the N-H+ stretching mode
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The 3-D calculation including the NH bending perpendicular to water plane, the NH bending parallel to water plane, the NH stretching
2904 cm-1 : the NH stretching
3037 cm-1 : overtone of the NH bending perpendicular to water plane
3112 cm-1 : overtone of the NH bending parallel to water plane
2904
3037
3112
The 3-D simulation & observed IR spectrum of TMA-H+-H2O (Ar tagged)
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IR spectra of TMA-H+-X
The major component of the N-H+
stretching mode is colored withorange
The frequency of the N-H+ stretching mode goes down gradually as DPA decreases
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Summary
■The Fermi resonance necessarily occurs in the H+ vibrations at the ~ 3000 cm-1 region
■The overtones of the N-H+ bending modes is coupled with the N-H+ stretching vibration
■To understand the real excess proton motion, we need to perform a multi-dimensional analysis (see MK13 : next presentation)
■The N-H+ stretch vibration frequency gradually goes down with DPA decrease
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IR spectra of TMA-H+-MeOH & TMA-H+-MeOH (Ar tagged)
■The Intensity alternation of the peaks is due to the dissociation efficiency of Ar
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IR spectra of Amine-H+-H2O & Amine-H+-H2O (Ar tagged)
■The Intensity alternation of the peaks also occurs
■Prominent peaks around 2800 cm-1 are attributed to the N-H+ stretching mode
(a)Obs.
(b)Calc.
IR and simulated spectra of TMA-H+-(H2O)1
B3LYP/6-31+G(d)Scaling factor : 0.9736 20
(a)Obs.
(b)Calc.
IR and simulated spectra of TMA-H+-(H2O)2
B3LYP/6-31+G(d)Scaling factor : 0.9736 21
(a)Obs.
(b)Calc.
(c)Calc.
ΔE0 = 0.0 kJ/molΔG = 0.0 kJ/mol
ΔE0 = +0.01 kJ/molΔG = +0.4 kJ/mol
3I
3II
IR and simulated spectra of TMA-H+-(H2O)3
ΔG@190 K
B3LYP/6-31+G(d)Scaling factor : 0.9736 22
Water 165.2Benzene 179.3Methanol 181.9Ethanol 185.6
Naphthalene 191.9Acetone 194.1Phenol 195.3Pyrene 207.7
Anthracene 209.7Azulene 221.1Pyridine 222.3
Trimethylamine 225.1
all units in kcal/mol
Proton affinity of some molecules
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