21 世紀 COE 外国旅費補助・成果報告

1/19

物理学第一教室　光物性研究室　 D2 　矢田祐之

2007 年 10 月 18 日（木）理学部４号館（宇宙物理教室）講義室 (414 号室）

21 世紀 COE外国旅費補助・成果報告

2/19

会議の概要•名称 : 　 The International Conference on Infrared, Millimeter, and Terahertz Waves (IRMMW-THz)

•場所 : 　 Cardiff, UK

•期間 : 2007/9/3~9/7

•規模： 18 カ国から 430 人以上が参加

4 つのパラレルセッション•概要：赤外波、ミリ波、テラヘルツ波の発生検出技術およびその応用を議論

（例 セキュリティ、天文、医療、通信、分光分析・・・）

カーディフ：ウェールズ地方の首都

人口： 30 万人　産業革命以降、カーディフ港からの石炭の積み出しで、飛躍的に発展した。

3/19

分野の概要

配向緩和 分子内振動 電子遷移分子間振動分子回転

X 線回折プラズマ振動

THz領域応用：Ｘ線と補完的なイメージング光源

1nm10nm

ミリ（マイクロ）波 近赤外

可視光

紫外 X線 線電波 中赤外遠赤外

3THz100m

30THz10m

300THz1m

3PHz100nm

300MHz1m

3GHz100mm

30GHz10mm

300GHz1m

本研究の対象は水の分光

4/19

テラヘルツ時間領域分光法

半導体素子( 光伝導アンテナ )

光サンプリング検出( 電気光学効果 )

超短パルスファイバーレーザー(50MHz, 780nm, 20mW, 90fs)

THz Time-Domain Spectroscopy (THz-TDS)

= 実時間電場波形を検出

→複素誘電率を測定できる。

サンプル

5/19

Picosecond Dynamics of Water and Heavy Water Investigated by Using Terahertz Time-Domain Attenuated

Total Reflection Spectroscopy

Hiroyuki YADA, Masaya NAGAI, and Koichiro TANAKA

Department of Physics, Kyoto University, Japan

IRMMW-THz 2007, Cardiff (September 3rd-7th )

This work is supported by Center for Diversity and Universality in Physics (CDUP).

WedB3-3

6/19

Background of this study

Forming and breaking of hydrogen bonding Picosecond timescale (MD)

Collectiverelaxation mode20 GHz(Dielectric measurement)

Intermolecular stretching vibration modeand libration mode5 THz, 14 THz(Raman and far-infrared spectroscopy)

Picosecond dynamics of water gives a basis for understanding the biochemical reaction in water, such as hydration dynamics (->WedB3-1).

Water dynamics in ps timescale

Individual mode ? 1.5 THz THz component (THz TDS)

Collective motions of dipole moments due to the fluctuation of hydrogen bonding network

7/19

Recent research on THz component

[1] C. Rønne, et al., J. Chem. Phys. 107, 5319 (1997).[2] C. Rønne, P. -O. Åstrand and S. R. Keiding, Phys. Rev. Lett. 82, 2888 (1999).

Am

pli

tud

e

• Rønne et al. made THz spectroscopy (~2.0 THz)

and found that THz component is Debye relaxation mode.

Dispersion of vibration modeTk

AmplitudeB3

2

8/19

Purpose of this study

To reveal the physical origin of the THz component

•Accurate measurements of temperature dependence of complex dielectric constants of water and heavy water have been made in wider frequency region [ 0.2 ~ 3.5 THz].

•Analysis taking into account vibration modes has been made to estimate the contribution of vibration mode.

9/19

THz Time-Domain Attenuated Total Reflection Spectroscopy

[1] N. J. Harrick, “Internal Reflection Spectroscopy”, Interscience, (1967).[2] H. Hirori et al., Jpn. J. Appl. Phys. 43, L1287-L1289 (2004). [3] H. Hirori et al., OPTICS EXPRESS 13, 10801 (2005).[4] M. Nagai et al., J. Int. Infrared Millimeter Waves 27, 505 (2006).

• Reflection-type measurement near the critical angle

more sensitive than normal reflection (->WedB3-1)

• Reference is easily measured by removing water.

A. ATR

C. Normal

020.~ r

10/19

8

6

4

2

0

Im[

]

43210

Frequency [THz]

i295 K (22 ºC)

10

8

6

4

2

0

Re[

]

rWater

8

6

4

2

0

Im[

]

43210Frequency [THz]

i

362 K (89°C)335 K (62°C)313 K (40°C)295 K (22°C)278 K (5°C) 267 K (-6°C)

10

8

6

4

2

0

Re

[] r

Water

8

6

4

2

0Im

[]

43210

Frequency [THz]

i295 K (22 ºC)

10

8

6

4

2

0

Re

[] r

Water

Temperature dependence

•Small increase in real part

•Significant increase in Imaginary part

-> GHz Debye mode

Temperature dependence of complex dielectric constants of water

Room temperature

•Rapid Increase in Im() in low frequency

-> GHz Debye mode

•Gradual increase in Im() in high frequency

-> Vibration in 5 THz

11/19

Temperature dependence of complex dielectric constants of heavy water

•The temperature dependence is almost the same with water.

->GHz Debye mode

10

8

6

4

2

0

Re[

] r

Heavy water

8

6

4

2

0

Im[

]

43210

Frequency [THz]

i

362 K (89°C)336 K (63°C)313 K (40°C)295 K (22°C)278 K (5°C)267 K (-6°C)

12/19

10080604020

0

Re

[] r

40302010

0

Im[

]

0.0001 0.001 0.01 0.1 1 10 100

Frequency [THz]

i363 K (90ºC)333 K (60ºC)313 K (40ºC)293 K (20ºC)279 K (6ºC)267 K (-6ºC)

Temperature dependence of the GHz Debye mode

D

S

i

11

[1] R. J. Speedy and C. A. Angell, J. Chem. Phys. 65, 851 (1976).[2] P. S. Yastremskii, J. Structural Chemistry 29, 483 (1988). [3] C. Rønne, et al., Phys. Rev. Lett. 82, 288 (1999).[4] G. A. Vidulich, D. F. Evans, and R. L. Key, J. Phys. Chem. 71, 656 (1985).

water

51 fix

13/19

Frequency [THz]

0.001

0.01

0.1

1

10

i

0.0001 0.001 0.01 0.1 1 10 100

i

WaterH2O 20 ºC

Decomposition into 4 components

21

320

211

122

1

3

022

0

2

2

11

11)(~

AAA

i

A

i

A

i

A

i D

S

[1] M. N. Afsar et al., J. Opt. Soc. Am., 67, 116 (1977). [2] U. Kaatze, J. Chem. Eng. Data 34, 371 (1989).[3] J. M. Alison et al., Meas. Sci. Tech. 2, 975 (1991). [4] A. N. Rusk et al., J. Opt. Soc. Am. 61, 895 (1971).

Intermolecular stretching vibration mode5.4 THz

Libration mode 14 THz

THz component1.5 THz

?Collective Relaxationmode20 GHz

14/19

THz component at room temperature

[1] M. N. Afsar and J. B. Hasted, L. J. Opt. Soc. Am., 67, 116 (1977) .

Rønne Amp 2 [fs]

H2O 1.90±0.4 170±40

D2O 2.07±0.11 147±8

Amp 2 [fs]

H2O 1.68±0.02 245±6

D2O 1.76±0.07 289±17

C. Rønne, et al., J. Mol. Liq. 101, 199 (2002).

Our results1.5

1.0

0.5

0.0

Im[

]

43210

Frequency [THz]

i

THz component

2.0

1.5

1.0

0.5

0.0

Re

[]

r

Water 295 K (22ºC)

We connect our data to far-infrared results [1].

The relaxation time is longer both in H2O and D2O.

15/19

Decomposition into 4 componentsWe reduce the fitting parameters for stretching vibration and libration mode.

[1] H. R. Zelsmann, J. Mol. Structure 350, 95 (1995).

Temperature dependences of amplitudes are determined so that integral of the imaginary part can be constant.

Temperature dependence of resonant frequencies are determined by referring to far-infrared result [1].

The values at room temperature are used.

20

320

211

122

1

3

022

0

2

2

11

11)(~

AAA

i

A

i

A

i

A

i D

S

16/19

Temperature dependence of the THz component

[1] C. Rønne, et al., J. Chem. Phys. 107, 5319 (1997).

TkAmplitude

B3

2

•The amplitude is almost constant. • Relaxation times are longer and almost constant.• Isotope shift is observed.

17090022

22 ..)(

)(

OD

OH

600

400

200

0

2 [fs

]

360340320300280

Temperature [K]

H2OD2O

RønneH2O D2O

5

4

3

2

1

0Am

plit

ude

[arb

. un

its]

360340320300280

Temperature [K]

H2OD2O

RønneH2O D2O

17/19

Discussion 1

[1] K. Okada, M. Yao, Y. Himejima, H. Kohno, and Y. Kajihara, J. Chem. Phys. 110, 3026 (1998).

Our findings

• Little temperature dependence of relaxation time of THz component

• Isotope shift of the relaxation time of THz component

T

P

491 K, 218 atm.

Liquid water

•Collective mode (Large)

•THz Debye mode (small)

This is observed in GHz dielectric measurement [1].

Supercritical waterThe temperature is high.The density is low.

•Collective mode

•THz Debye mode (remain)

If it is individual mode.

individual mode ?

18/19

Discussion 2

[1] K. Okada, et al., J. Chem. Phys. 110, 3026 (1999).[2] A Luzar and D. Chandler, Nature 379, 55 (1996).

9502

2

22

22 .)(

)(

OD

OH

m

m

OD

OH

800

600

400

200

0

2 [f

s]

360340320300280

Temperature [K]

H2OD2O

H2O CollisionD2O Collision

17090022

22 ..)(

)(

OD

OH

• 10 % of hydrogen bondings are broken. (Thermal experiment)

• Forming and breaking of hydrogen bondings ~ 0.3 ps (MD)

THz component is Individual mode.

Collision model

Tk

m

rnv

l

Beff

24

1

Hit

misseffr relV

Hard sphere

Individual mode

Collective mode

19/19

Summary

• We have determined temperature dependence of dielectric constants of water and heavy water in the range from 0.2 THz to 3.5 THz, -6 ºC to 91 ºC by THz-TD-ATR spectroscopy.

• We have decomposed the dielectric constants into four components, GHz Debye mode, THz Debye mode, stretching vibration mode, and libration mode.

• In terms of the temperature dependence and isotope shift, THz component has been assigned to individual relaxation mode.

成果：研究発表および共同研究（ ATR 法の技術協力）の議論ができ、意義深い国際会議であった。