Intermolecular Dynamics of Room-Temperature Ionic Liquids: Femtosecond Optical Kerr Effect Measurements on 1-Alkyl-3- methylimidazolium Bis ((trifluoromethyl)sulfontl)imides Byung-Ryool Hyun, Sergei V. Dzyuba, Richard A. Bartsch, and Edward L. Quitevis J. Phys. Chem. A 2002, 106,

1.Introduction 2.Experimental Methods A.Synthesis and Physical Characterization B.OHD-RIKES Apparatus 3.Experimental Results 4.Analysis and Discussion A.Temporal Response B.Spectral Response 5.Concluding Remark

Ionic Liquid1.Introduction 100 o C 이하의 온도에서 액체로 존재하는 이온성 염 Fig1. 일반적인 ionic liquid 의 구조식 [1] Fig2.ionic 의 대표적인 예와 구조식 [1] 1 -Butyl-3-methylimidazolium hexafluorophosphate Ionic liquid 의 장점  Green designer solvents for use in catalysis  Chemical synthesis  Separations

 Molecular dynamics of ionic liquids  Intermolecular interaction in ionic liquid  sub-ps time region  ultrafast time-resolved technique  Raman-induced Kerr Effect(RIKE) measurement

2.Experimental Methods A.Synthesis and Characterization Fig3.Structure of1-Alkyl-3-methylimidazolium bis((trifluoromethyl)sulfontl) imides and synthetic scheme anion alkyl chain cation C2,C4,C5,C6,C8,C10

TABLE1:Physical Properties of Ionic Liquids at C C C C C C =density; =viscosity  Densities were measured by use of 1mL pycnometers or an Anton-PARR density Measurement System  Dynamic viscosities were measured with an Oswald viscometer

B.OHD-RIKES Apparatus optical Input 에 따른 매질의 굴절률의 변화가 생기는 현상 Pump beam Probe beam Kerr medium Polarizer Analyser OKE(Optical Kerr Effect) [2]

Polarizer1(Linear polarizer) Polarizer2(Linear polarizer) Transmission axis at <45+1 o Wave plate Kerr medium OHD(Optical Heterodyne Detector) [2] Fast axis Slow axis

45 o 로선형편광된 polarizer1 Isotropic 한 sample -45 o 로선형편광된 polarizer2 Jones matrices(Homodyne)

Jones matrices(Heterodyne) Wave plate Fast axis vertical -45 o 로선형편광된 polarizer2 Isotropic 한 sample 46 o 로선형편광된 polarizer1 I local oscillator I signal I heterodyne

RIKE(Raman Induced Kerr Effect) [3] 3 차비선형분극계수 는 의 값이 분자의 Raman 천이 고유주파수 에 접근하면 증가한다

Fig4.Schematic of optical heterodyne-detected Raman-induced Kerr effect spectroscopy (OHD-RIKES) apparatus[4] :  Ti:sapphire laser (800nm,40fs) 50mW PUMP beam, 10mW PROBE beam  BS : pellicle beam splitter  L : 10cm focal length  lock-in amplifier  P1,P2,P3 : Glane Taylor air-gap polarizer  PD : Si photodiode P1 P2 P3 PD LIA CHOPPER L SAMPLE Delay stage B/S L probe pump Ti:sapphire laser computer

Fig5.Normalized OHD-RIKES signal forC2,C4,C5,C6,C8 and C10 at room temperature and ambient pressure. Signal are offset in order to better show the difference 3.Experimental Result Electronic response Nuclear response

Fig6.Semilogarithmic plot comparing OHD-RIKES responses for C5(solid curve) and C8(dashed curve) at short time(t 1.5ps). The vertical lines above the OHD-RIKES for C5 indicate the 230-fs-period oscillation 230fs Intermolecular vibration noise level

4.Analysis Discussion A.Temporal Response The OHD-RIKES signal is the convolution of and the nonlinear impulse response, : The impulse response is given by the sum of an electronic response function, and a nuclear response function, : long-time tail of the nuclear response is associated with diffusive dynamics arising from collective reorientation short time behavior of nuclear response is mainly associated with nondiffusive dynamics arising from the intermolecular vibrational motions

Fig7.Typical fit of the OHD-RIKES data for C5 between 0.5 and 8 ps to a biexponential decay function TABLE2:OHD-RIKES Biexponential Fit Parameters C C C C C ps Intermolecular response

B.Spectral Response In the Fourier-transform procedure, the OHD-RIKES response is represented by a frequency response function Where denotes a forward complex Fourier-transform Operator. Is obtained by the complex division of the Fourier-transform of the OHD-RIKES signal,,by the Fourier-transform of the pulse autocorrelation

Is the Bucaro-Litovitz line shape function Is the antisymmetrized Gaussian line shape function C C C C C TABLE3:Line Shape Parameters for Fit of Reduced Spectral Densities The reduced spectral densities are well described by the sum of two bands

Fig8.Reduced spectral densities for C2,C4,C5,C6, and C8 with fits to the superposition model. The solid curve in each plot is given by the sum of the Bucaro-Litovitz function(dashed curve) and the antisymmetrized Gassial function (dotted curve) ~22cm -1 ~84cm -1

5.Concluding Remarks 140cm It is proposed that the 140cm -1 oscillation arises from collective motions of locally ordered domains in the liquid 2. The intermolecular vibrational spectra for these RITLs obtained from the reduced OHD-RIKES data by using a Fourier transform procedure extend from 0to 200cm -1 and are bimodal with a low-frequency component at ~22cm -1 and a high-frequency component at ~84cm -1

[1] Reference [2]Nonlinear Optics Robert W. Boyd [3] 비선형광학 이범구 [4]Femtosecond Optics Kerr Effect Studies of Liquid Methyl Iodide, Edward L, Quitevis and Manickam Neelakandan, J. Phys. Chem 1996,100,10005