Molecular dynamics of liquid acetone determined by Depolarized Rayleigh and low-frequency Raman scattering spectroscopy M.G. Giorgini1, F. Palombo2, M. Paolantoni2, P. Sassi2 and A. Morresi2 1 Department of Physical and Inorganic Chemistry, University of Bologna, Viale del Risorgimento 4, I-40136 Bologna, Italy. Email: mariagrazia.giorgini@unibo.it 2 Department of Chemistry, University of Perugia, Via Elce di Sotto 8, I-06123 Perugia, Italy. ABSTRACT Depolarized Rayleigh and low-frequency Raman scattering (DRS-LFR) spectra of liquids such as polar solvents enable the slow to ultrafast molecular dynamics of the condensed phase to be assessed. Time correlation functions of the polarizability anisotropy can be extracted from the (DRS-LFR) spectra, and suitably compared with corresponding responses from OKE time-resolved experiments [1]. The application of such frequency-domain approach to the study of dynamics of the liquid acetone at different temperatures (T=5.8–44.3 °C) revealed the presence of ultra-fast, fast (sub-picoseconds) and slow (picoseconds) processes. The slow dynamical process, which is attributable to the collective orientational dynamics, shows an increasing rate with the temperature (1=1.45 ps, at T=5.8 °C, and 1.01 ps, at 44.3°C) and closely compares with the characteristic time obtained from the long-time Kerr transient decay (1,DRS=1.17 ps, at T=25.1 °C, and 1,OKE=1.09 ps, at 24.0°C) [2]. Being acetone an approximate oblate symmetric-top rotor,[3] a unique component of the anisotropy polarizability tensor (0) activates the DRS spectrum, whilst only the anisotropy polarizability derivative tensor (k0, where k indicates a totally symmetric normal mode) activates the anisotropic Raman spectrum. The reorientational motion of acetone proved to be better described by a model based on microviscosity rather than the Stokes-Einstein-Debye hydrodynamic theory. The fast process results largely temperature independent (2=0.42 ps, at T=5.8 °C, and 0.38 ps, at 44.3°C) and may be attributed to a structural relaxation of “solvent cages” around librating molecules in the liquid. Evidences of librational dynamics were obtained from the analysis of reduced susceptibility spectra, ”(̃). Information obtained from the spectra of neat liquid acetone will be applied to the study of complex systems such as ionic solutions of acetone, in a further development of this work. REFERENCES [1] McMorrow, D., Lotshaw, W. T., and Kenny-Wallace, G. A., “Femtosecond optical Kerr studies on the origin of the nonlinear responses in simple liquids” IEEE Journal of Quantum Electronics 24 (2), 443-454 (1988) [2] Shirota, H., Fujisawa, T., Fukazawa, H., and Nishikawa, K., “Ultrafast dynamics in aprotic molecular liquids: a femtosecond Raman-induced Kerr effect spectroscopic study” Bulletin of the Chemical Society of Japan 82 (11), 1347-1366 (2009) [3] Bródka, A., and Zerda, T. W., “Dynamics of liquid acetone: Computer simulation” Journal of Chemical Physics 104 (16), 6313-6318 (1996)

Molecular dynamics of liquid acetone determined by Depolarized Rayleigh and low-frequency Raman scattering spectroscopy.

GIORGINI, MARIA GRAZIA
2011

Abstract

Molecular dynamics of liquid acetone determined by Depolarized Rayleigh and low-frequency Raman scattering spectroscopy M.G. Giorgini1, F. Palombo2, M. Paolantoni2, P. Sassi2 and A. Morresi2 1 Department of Physical and Inorganic Chemistry, University of Bologna, Viale del Risorgimento 4, I-40136 Bologna, Italy. Email: mariagrazia.giorgini@unibo.it 2 Department of Chemistry, University of Perugia, Via Elce di Sotto 8, I-06123 Perugia, Italy. ABSTRACT Depolarized Rayleigh and low-frequency Raman scattering (DRS-LFR) spectra of liquids such as polar solvents enable the slow to ultrafast molecular dynamics of the condensed phase to be assessed. Time correlation functions of the polarizability anisotropy can be extracted from the (DRS-LFR) spectra, and suitably compared with corresponding responses from OKE time-resolved experiments [1]. The application of such frequency-domain approach to the study of dynamics of the liquid acetone at different temperatures (T=5.8–44.3 °C) revealed the presence of ultra-fast, fast (sub-picoseconds) and slow (picoseconds) processes. The slow dynamical process, which is attributable to the collective orientational dynamics, shows an increasing rate with the temperature (1=1.45 ps, at T=5.8 °C, and 1.01 ps, at 44.3°C) and closely compares with the characteristic time obtained from the long-time Kerr transient decay (1,DRS=1.17 ps, at T=25.1 °C, and 1,OKE=1.09 ps, at 24.0°C) [2]. Being acetone an approximate oblate symmetric-top rotor,[3] a unique component of the anisotropy polarizability tensor (0) activates the DRS spectrum, whilst only the anisotropy polarizability derivative tensor (k0, where k indicates a totally symmetric normal mode) activates the anisotropic Raman spectrum. The reorientational motion of acetone proved to be better described by a model based on microviscosity rather than the Stokes-Einstein-Debye hydrodynamic theory. The fast process results largely temperature independent (2=0.42 ps, at T=5.8 °C, and 0.38 ps, at 44.3°C) and may be attributed to a structural relaxation of “solvent cages” around librating molecules in the liquid. Evidences of librational dynamics were obtained from the analysis of reduced susceptibility spectra, ”(̃). Information obtained from the spectra of neat liquid acetone will be applied to the study of complex systems such as ionic solutions of acetone, in a further development of this work. REFERENCES [1] McMorrow, D., Lotshaw, W. T., and Kenny-Wallace, G. A., “Femtosecond optical Kerr studies on the origin of the nonlinear responses in simple liquids” IEEE Journal of Quantum Electronics 24 (2), 443-454 (1988) [2] Shirota, H., Fujisawa, T., Fukazawa, H., and Nishikawa, K., “Ultrafast dynamics in aprotic molecular liquids: a femtosecond Raman-induced Kerr effect spectroscopic study” Bulletin of the Chemical Society of Japan 82 (11), 1347-1366 (2009) [3] Bródka, A., and Zerda, T. W., “Dynamics of liquid acetone: Computer simulation” Journal of Chemical Physics 104 (16), 6313-6318 (1996)
New outlook on molecular liquids: from short scale to long scale dynamics
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F. Palombo; P. Sassi; M. Paolantoni; A. Morresi; M.G. Giorgini
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Utilizza questo identificativo per citare o creare un link a questo documento: http://hdl.handle.net/11585/108477
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