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Non-Markovian nature of the fluctuation of the polarizability in molecular liquids by time-domain and frequency-domain measurements


  • This article is from the ECONOS part of the joint special issue on the European Conference on Nonlinear Optical Spectroscopy (ECONOS 2012) with Guest Editors Johannes Kiefer and Peter Radi and the II Italian Conference of the National Group of Raman Spectroscopy and Non-Linear Effects (GISR 2012) with Guest Editor Maria Grazia Giorgini.


We measured the low-frequency regions of several molecular liquids at various temperatures using time-domain and frequency-domain spectroscopy to investigate the origin of the relaxation mode. We employed high-resolution light scattering spectroscopy in the frequency domain and femtosecond optical Kerr effect spectroscopy in the time domain. By comparing the light scattering spectra of a relaxation mode with a Lorentzian function fitted to the spectra, we found that the spectra only follow the Lorentzian curve within a limited wavenumber range around the peak, which is comparable with the half width at half maximum of each Lorentzian curve. We evaluated the spectral range and compared it with the half width of the Lorentzian curve for several liquid samples at various temperatures together with the data obtained by the time-domain method. We found that they were surprisingly correlated with each other regardless of the sample and temperature used, which indicates that the relaxation mode systematically deviates from the Lorentzian function. This suggests that the dynamics governing the relaxation mode is clearly non-Markovian. Copyright © 2013 John Wiley & Sons, Ltd.