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)

10

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+

11

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

14

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)

15

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

16

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

17Thank you for your attention

Apr 19, 2013

18

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

19

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

23

24

ΔPA dependence of the excess proton vibration frequency