Low-frequency depolarized Raman-spectral density of liquid water from femtosecond optical Kerr-effect measurements: Lineshape analysis of restricted translational modes

Abstract

A high-quality depolarized Raman-spectrum is obtained in the frequency range 0 p o p 600 cm À1 by Fouriertransformation of time-resolved dual-color heterodyne-detected optical Kerr-effect data of liquid water at 0 C. The time-resolution was sufficient to fully capture the restricted translational and part of the hindered rotational region of the Raman spectrum. This low-temperature spectrum is used to test the applicability of stochastic line broadening theories. A conventional Kubo line shape analysis indicates that restricted translational modes involving hydrogen-bond bending and stretching motions are predominantly in the slow modulation limit at temperatures close to the melting point. However, a pronounced residual fine structure exists which cannot be fully accounted for by the theory in its standard form. Instead, we propose to apply a modified Kubo model based on truncating its continued-fraction representation at a finite order N including a convolution with a quasi-static structural inhomogeneity in the liquid. In particular, a quantitative agreement of our experimental data with such an inhomogeneous N-state random-jump model is interpreted with a discrete size distribution of aggregates which can interconvert on a time scale of about 500 fs by breaking and making of hydrogen bonds.

Optical Kerr effect of liquid and supercooled water: The experimental and data analysis perspective

“…Few phenomenological models have been utilized to analyse the whole time-dependent OKE response in liquid water [42][43][44] . As well as, the mode-coupling theory has been used to simulate the water response 1,4,28 .…”

Probing the hydrogen-bond network of water via time-resolved soft X-ray spectroscopy

“…20,21,22,23,24 There is also abundant literature on the low-frequency spectral response of water between a few wavenumbers and the O···O stretching vibration ν O···O . 25,26,27,28,29,30 Static x-ray spectroscopy experiments have been used to investigate the oxygen K-edge of water, the near-edge region of which is shown in Fig. 1B.…”

Water Dynamics at Protein Interfaces: Ultrafast Optical Kerr Effect Study

“…1,2 Therefore, the understand- 27 ing of water at these interfaces is of great importance in 28 chemistry and biology. 3À7 29 Water molecules in aqueous solutions of proteins can be 30 grouped into three broad categories: (1) the internal waters that 31 occupy specific sites in the protein and can be identified crystal- 32 lographically, (2) the hydration water immediately surrounding 33 the protein, and (3) bulklike water. Hydration water has direct 34 contact with the protein surface and plays an essential role in 35 protein folding interaction of water with the hydrophobic groups, 36 causing them to collapse and become isolated in the protein core.…”