INFRARED SPECTROSCOPIC STUDY ON FERMI RESONANCE OF THE EXCESS PROTON VIBRATION IN BINARY CLUSTERS Ryunosuke SHISHIDO, Asuka FUJII Department of Chemistry, Graduate School of Science, Tohoku University, Japan Jer-Lai KUO Institute of Atomic and Molecular Sciences, Academia Sinica, Taipei, Taiwan June 17,2013 MK12

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 Introduction M. 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  PA decreases Decreasing  PA (  PA: PA difference of A and B)

3 This study ◆ Does the magnitude of the low-frequency shift of the proton vibration depend only on  PA? ◆ 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  PA (CH 3 ) 3 N-H + -X (Protonated trimethylamine(TMA) –X cluster) X = Ar, N 2, CO, C 2 H 2, H 2 O, CH 3 OH, C 2 H 5 OH, CH 3 COCH 3,C 2 H 5 OC 2 H 5, NH 3, CH 3 NH 2, and (CH 3 ) 3 N Amine-H + -H 2 O Amine : NH 3, CH 3 NH 2, (CH 3 ) 2 NH, and (CH 3 ) 3 N We found the Fermi resonance of the excess proton vibration with overtones of N-H + bending modes TMA H+H+

5 + mass selection v=1 h IR dissociation mass selection 1st-Qmass 2nd-Qmass octopoleionguide [TMA-H + -X] [TMA-H + ] X discharge Infrared photodissociation spectroscopy Experiment

6 IR and simulated spectra of TMA-H + -X ■ The N-H + stretching frequency goes down as  PA between TMA and X decreases ■ When the N-H + stretching frequency gets into around 3000 cm -1 region, complicated Fermi resonance is always seen Scaling factor :

7 ΔPA dependence of the excess proton vibration frequency ■ The frequencies of the excess proton vibrations are low-frequency shifted with  PA 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  PA 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 H 3 N-H + -NH 3 ) ?

9  PA change by changing the cluster size of water molecules ■ The Fermi resonance changes by changing the cluster size of water molecules free OH ν OH N-H + ν OH (PA of the water moiety changes)

10  PA changes by changing the amine moiety ■ The Fermi resonance changes by the change of the amine moiety free OH free NH N-H +

11 TMA-H + -X, TMA-H + -(H 2 O) n, and Amine-H + -H 2 O  The Fermi resonance is a general phenomenon in the N-H + --X systems at cm -1 region  The multi-dimensional motion occurs in this region

12 Assignments of the coupling partner with the N-H + stretching mode According to the spectrum of TMA(d 9 )-H + -H 2 O, ■ 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 + -H 2 O & TMA-H + -H 2 O (Ar tagged) ■ All the bands show narrowing through Ar attachment According to the spectrum of TMA-H + -H 2 O(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 The 3-D simulation & observed IR spectrum of TMA-H + -H 2 O (Ar tagged) TMA-H + -H 2 O (Ar tagged)

15 IR spectra of TMA-H + -X The major component of the N-H + stretching mode is colored with orange The frequency of the N-H + stretching mode goes down gradually as  PA 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  PA decrease

17 Thank 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 + -H 2 O & Amine-H + -H 2 O (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 + -(H 2 O) 1 B3LYP/6-31+G(d) Scaling factor :

(a)Obs. (b)Calc. IR and simulated spectra of TMA-H + -(H 2 O) 2 B3LYP/6-31+G(d) Scaling factor :

(a)Obs. (b)Calc. (c)Calc. ΔE 0 = 0.0 kJ/mol ΔG = 0.0 kJ/mol ΔE 0 = kJ/mol ΔG = +0.4 kJ/mol 3I3I 3II IR and simulated spectra of TMA-H + -(H 2 O) 3 K B3LYP/6-31+G(d) Scaling factor :

all units in kcal/mol Proton affinity of some molecules 23

24 ΔPA dependence of the excess proton vibration frequency