Femtosecond Optical Kerr Effect Studies of Liquid Methyl Iodide

Abstract

The collective polarizability anisotropy dynamics of liquid methyl iodide at room temperature and ambient pressure was studied by using optical heterodyne-detected Raman-induced Kerr effect spectroscopy (OHD-RIKES) with 45 fs laser pulses. The OHD-RIKES data are analyzed by using both the model-dependent approach, which assumes four distinct temporal responses, and the model-independent Fourier transform approach, which generates a spectral density. Near zero time, the OHD-RIKES transient is dominated by the instantaneous electronic response. The short-time nuclear response is characterized by two components. The first component is interpreted as arising from an inhomogeneously broadened (fwhm ≈ 62 cm -1 ) underdamped intermolecular vibrational mode with a mean frequency of ∼60 cm -1 . The second component is an intermediate quasi-exponential response with a 1/e time constant of ∼200 fs. At longer times, the OHD-RIKES transient decays exponentially with a 1/e time constant of 1.76 ( 0.05 ps, which corresponds to the collective reorientation time of CH 3 I. The spectral density peaks at ∼24 cm -1 and has a fwhm of ∼80 cm -1 . The spectral density can be well fitted by an ohmic distribution function with ω c ≈ 30 cm -1 . The spectral density obtained from the OHD-RIKES data is consistent with previously measured depolarized Rayleigh scattering and low-frequency far infrared absorption spectra for liquid CH 3 I.

Cation and anion substitution effects on the ultrafast dynamics of interionic interaction in imidazolium based ionic liquids

“…6 ] well agrees with the previously reported data [23,24]. As shown in Figure 1, we observed two-period oscillations in the fs-OHD-RIKES signal of [31][32][33][34][35][36][37]. As for the ILs systems, researchers generally converted their time domain fs-OHD-RIKES signals into frequency domain through FFT theorem, and then decomposed the fs-OHD-RIKES FFT spectra with either a summation of one Ohmic or BL function and several antisymmetrized Gaussian functions or a summation of several BOs [18][19][20][21][22][23][24][25][26].…”

“…The BO model has been successfully employed to analyze the fs-OHD-RIKES signal in time domain in simple molecular liquid [31][32][33][34][35][36][37]. Here, we applied the BO model into the ILs system.…”

“…(6), where this exponential decay form was the most commonly used formula for the OD oscillator in refs. [31,33,34].…”

Optically-heterodyne-detected optical Kerr effect (OHD-OKE): Applications in condensed phase dynamics

“…This component is assigned to di usive molecular reorientation. Some quite detailed attempts have been made to analyse the relaxation times in terms of the Debye model of orientational relaxation [42,47,49], which predicts, for a molecule represented by an ellipsoidal shape with two equal axes [57±59],…”

Molecular dynamics of thiophene homologues investigated by femtosecond optical Kerr effect and low frequency Raman scattering spectroscopies

“…By these spectroscopic techniques in time and frequency domains, intermolecular dynamics of a simple molecular liquid such as CS 2 , 5,6,11,25 halogenated methanes, 11,32,39 benzene 6,11,39 and its derivatives, 18,21 and more complicated hydrogen-bonded molecular liquid such as water, [22][23][24] alcohol, 16 ethylene glycol 19 and their solutions 8,9,20 has been studied. General agreement exists in the intermolecular dynamics in terms of relaxation modes and oscillation modes that are closely related to the microscopic environment in which the molecules are located.…”