Dynamics of intermolecular interactions in CCl₄via the isotope effect by femtosecond time-resolved spectroscopy

Abstract

We report our study on the ultrafast dynamics of intermolecular interactions in liquid CCl4. A transient transmission time domain signal, obtained in the 40 ps delay range, exhibits beating at the difference frequency of the totally symmetric stretching vibrations of the tetrachloride isotopologues. We show that the spectra obtained as the windowed Fourier transform of different parts of the time domain signal in the range of this totally symmetric vibration, split due to the isotope effect, carry the information about the dynamics of the coherently excited, coupled molecules. We use a simple theoretical model in order to prove that the intermolecular interaction influences the relative amplitudes of the isotopologue peaks in the spectrum. Moreover, we demonstrate that the pump induced coherence in the system leads to additional strengthening of the interaction, which can be observed in the spectra obtained from the experimental time domain signal.

The influence of interactions between isotopoloques on coherent, ultrafast vibrational dynamics of liquid C2Cl4

“…The strong pump pulse coherently excites molecules in a medium, which, in turn, modifies transmission of the delayed pulse. The parameter, which is directly measured, is the intensity of the transmitted probe pulse in the case of the transient transmission experiment 1 and the change of transmitted probe pulse polarization in the case of the optical Kerr effect experiment. 23,24 Both variables carry information about the nonlinear refractive index, which becomes modulated with all frequencies of intra-and inter-molecular vibrations under the condition that these frequencies are less than the spectral width of the pump pulse.…”

“…In both techniques we obtain the modulation of the nonlinear refractive index of a medium with vibrational frequencies of both intramolecular and intermolecular modes. 1,19 In the spectral range 200-600 cm À1 the intramolecular symmetric stretching vibrations are of particular interest for us, because the apparent isotopic splitting of their spectral bands is the subject of discussion in the present paper. Application of two techniques allowed us to separate the isotropic response, independent of molecular rotations, and anisotropic response.…”

“…We have shown in our previous paper on CCl 4 , 1 that, due to the natural abundance of Cl isotopes, the isotopically split Raman band of the symmetrical stretching vibration carries the information about intermolecular interactions in a liquid. It manifests in different ratios of component peak heights and becomes more apparent when molecules are coherently excited.…”

“…2 In such a configuration the effect of intermolecular coupling is strong enough to be observed in a coherent response of the system. 1 In our previous paper 1 we came to the conclusion that the strength and dynamics of intermolecular interactions between isotopoloques in liquids, composed of molecules containing a few Cl isotopes, can be read out from the structure of the isotopically split Raman band, obtained as FFT of the femtosecond time-resolved signal. In order to support this idea and to study the dependence of a coherent response on the local order in a liquid, in the present paper we take into account a molecule which also has four Cl atoms but has different symmetry to carbon tetrachloride, i.e.…”

“…The natural abundance of chlorine isotopes in the ratio 75.77% of 35 Cl and 24.23% of 37 Cl should result in isotopic splitting of infrared and Raman bands. 1,12,17 The fine structure of these bands corresponds to the contributions of five isotopologues X 35 Cl 4 , X 35 Cl 3 37 Cl, X 35 Cl 2 37 Cl 2 , X 35 Cl 37 Cl 3 , X 37 Cl 4 , occurring with the distributions 32.96%, 42.16%, 29.22%, 4.31% and 0.35% respectively. 1,17 Although this problem has been widely studied in CCl 4 , 1,18 one can hardly find any appropriate papers on tetrachloroethylene.…”