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Ultrafast memory loss and energy redistribution in the hydrogen bond network of liquid H 2 O. M. L. Cowan et al ., Nature, 434 , 119‐202 (2005). MIYASAKA Laboratory Akiko NAGAFUJI. Contents. Introduction ・ Anomaly of water ・ Vibrational modes of H 2 O ・ OH stretching vibration

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Ultrafast memory loss and energy redistribution in the hydrogen bond network of liquid H 2 O


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slide1

Ultrafast memory loss and energy redistribution

in the hydrogen bond network of liquid H2O

M. L. Cowan et al., Nature, 434, 119‐202 (2005)

MIYASAKA Laboratory

Akiko NAGAFUJI

contents
Contents
  • Introduction

・Anomaly of water

・Vibrational modes of H2O

・OH stretching vibration

  • Experimental

・Nanofluidic sample cell

・Principle of photon echo & transient grating

・Experimental set-up

  • Results & Discussion
  • Summary
introduction
Introduction

Water

The density of ice …

smaller than that of liquid water

Melting point & boiling point …

anomalously high temperature

Masakazu Matsumoto et al., Nature, 416, 409 (2002)

Because of

hydrogen bond network!!

introduction1
Introduction

Vibrational modes of H2O

Asymmetric stretch mode

(liquid H2O … 3430 cm-1)

Symmetric stretch mode

(liquid H2O … 3210 cm-1)

Bending mode

(liquid H2O … 1650cm-1)

introduction2

The transition frequency of an individual OH stretching oscillator in hydrogen bond network

The local environment!!

Introduction

OH stretching vibration

  • Free OH group…(a)

Very sharp!!

  • Hydrogen-bonded OH group…(b)

Inhomogeneous broadening!!

Erik T. J. Nibbering et al., Chem. Rev., 104, 1887 (2004)

experimental
Experimental

Sample cell

Before…

  • The high optical density of the OH stretching mode in pure H2O
  • Parasitic window signals in conventional samples

Hinder attempts to access the fastest relaxation processes of liquid water in pure H2O

Nanofluidic sample cell!

Windows & water layer

Extremely thin!!

experimental1
Experimental

What is photon echo ?

Pulse 1⇒Excitation (coherent polarization)

Pulse 2⇒Input of phase information

Pulse 3 ⇒Read of the information

experimental2
Experimental

Transient grating (τ=0)

(過渡回折格子)

Pulse 1 & Pulse 2

arrive simultaneously…

Interference pattern

Incidence of Pulse 3…

Bragg diffraction!!

experimental3
Experimental

Stimulated photon echo

The coherent polarization occurred by Pulse 1 is preserved during the delay time τ…

Interference can take place between the coherent polarization and the electric field of Pulse 2 !!

Photon echo signal is generated by Pulse 3!!

experimental4

1

2

3

Sig.

Ref.

τ

T

T

τ

-tRS

Experimental

Experimental set-up

τ…the lower part of roof mirror

T…translation stage

tRS…pulse 1, 2, 3 ⇒compensating plate

  • Three pulses…~1 mJ, 70 fs, 3350 cm-1 (the center of the OH stretching band)
  • Photon echo signal…heterodyne detection by spectral interferometry
results discussion

The strong anharmonicity of the OH stretching oscillator

Erik T. J. Nibbering et al., Chem. Rev., 104, 1887 (2004)

Results & Discussion
  • The positive peak⇒reduced absorption (bleaching) & stimulated emission
  • The negative peak ⇒excited state absorption

At T=0

The absorption below 3000 cm-1 & the bleaching above 3500 cm-1…very fast decay!!

The bleaching between 3170 and 3400 cm-1…slower decay & picosecond timescale rise!!

results discussion1

…(1)

Results & Discussion

Anisotropy

(偏光異方性解消)

Electric field of the pump light

Selective excitation!!

Rotational diffusion of the selectively excited molecules

results discussion2

parallel

perpendicular

anisotropy

Results & Discussion

◎In the case of H2O…

  • Intermolecular transfer of the OH stretch excitation (faster than 100 fs)
  • The orientational diffusion of the OH groups (4.0±0.4 ps)

(Sander Woutersen et al., Nature, 402, 507 (1999))

◎Parallel & perpendicularpolarization conditions…

  • Fast decay (95 fs)
  • Slower rise (1.3 ps)

The decay of the anisotropy

…very fast!! (75 fs)

The fast energy transfer!!

results discussion3

…(2)

τor : the orientational diffusion time

[OH] : the concentration of molecules containing an OH group

r0 : the Förster radius

T1 : the lifetime of the excited state

Results & Discussion

“Resonant intermolecular transfer of vibrational energy in liquid water”

(Sander Woutersen et al., Nature, 402, 507 (1999))

τor=4.0±0.4 ps

ro=2.10±0.05Å T1=740 fs

[OH]=111M

◎In the HDO : D2O…

The decay of anisotropy

⇒ equation (2)

◎In liquid H2O…

Instantaneous decay!!

results discussion4
Results & Discussion

Energy transfer

The decay of the anisotropy is very fast. ⇒ 75 fs!!

The transfer process…

dipole-dipole interaction (Förster transfer mechanism)

But!!

The detail mechanism … not yet analyzed!!

Quadrupole-quadrupole interaction??

Anharmonic coupling ??

(quadrupole:四極子)

results discussion5
Results & Discussion

◎Fast component…

The 95 fs decay ⇒ depopulation of the ν=1 state

◎Slow component…

The 1.3 ps rise ⇒ heating effects associated with vibrational relaxation

◎Anisotropy…

The 75 fs decay ⇒ energy transfer among the OH stretching vibrations

Shorter than the 700 fs time constant in a diluted 6:1 D2O:H2O mixture

The high concentration of OH stretching oscillator

⇒rapid intermolecular transfer of vibrational energy!!

Sander Woutersen et al., Nature, 402, 507 (1999)

results discussion6
Results & Discussion

◎On-diagonal

(bleaching & stimulated emission)

  • At T=0 fs…
  • Peak is stretched along the diagonal, indicating inhomogeneous broadening.
  • At T=50 fs…
  • This inhomogeneity is almost entirely lost.
  • By 100 fs…
  • It is completely gone.

◎Off-diagonal (excited state absorption)

Peak decays on the same timescale.

Ultrafast structural variation!!

summary
Summary
  • The fastest relaxation processes of liquid water in pure H2O can be observed by using a specially designed, ultrathin sample cell.
  • This work demonstrates the ultrafast energy transfer process and structural changes in the hydrogen bond network of liquid H2O.