Anisotropic X-Ray Scattering of Transiently Oriented Water

Open Access

Anisotropic X-Ray Scattering of Transiently Oriented Water

Kyung Hwan Kim, Alexander Späh, Harshad Pathak, Cheolhee Yang, Stefano Bonetti, Katrin Amann-Winkel, Daniel Mariedahl, Daniel Schlesinger, Jonas A. Sellberg, Derek Mendez, Gijs van der Schot, Harold Y. Hwang, Jesse Clark, Owada Shigeki, Togashi Tadashi, Yoshihisa Harada, Hirohito Ogasawara, Tetsuo Katayama, Anders Nilsson, and Fivos Perakis

Phys. Rev. Lett. 125, 076002 – Published 11 August 2020

Abstract

We study the structural dynamics of liquid water by time-resolved anisotropic x-ray scattering under the optical Kerr effect condition. In this way, we can separate the anisotropic scattering decay of 160 fs from the delayed temperature increase of $\sim 0.1 K$ occurring at 1 ps and quantify transient changes in the O-O pair distribution function. Polarizable molecular dynamics simulations reproduce well the experiment, indicating transient alignment of molecules along the electric field, which shortens the nearest-neighbor distances. In addition, analysis of the simulated water local structure provides evidence that two hypothesized fluctuating water configurations exhibit different polarizability.

Received 28 April 2020
Accepted 8 July 2020

DOI:https://doi.org/10.1103/PhysRevLett.125.076002

Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article’s title, journal citation, and DOI. Funded by Bibsam.

Published by the American Physical Society

Physics Subject Headings (PhySH)

X-ray lasers

Water

Molecular dynamics Ultrafast pump-probe spectroscopy X-ray diffuse scattering

Condensed Matter, Materials & Applied Physics

Authors & Affiliations

Kyung Hwan Kim^1,2,*, Alexander Späh¹, Harshad Pathak¹, Cheolhee Yang ², Stefano Bonetti ^1,3, Katrin Amann-Winkel¹, Daniel Mariedahl¹, Daniel Schlesinger ^1,4, Jonas A. Sellberg⁵, Derek Mendez⁶, Gijs van der Schot ⁷, Harold Y. Hwang⁸, Jesse Clark⁹, Owada Shigeki¹⁰, Togashi Tadashi¹⁰, Yoshihisa Harada ¹¹, Hirohito Ogasawara⁹, Tetsuo Katayama¹⁰, Anders Nilsson ¹, and Fivos Perakis ^1,†

¹Department of Physics, AlbaNova University Center, Stockholm University, SE-10691 Stockholm, Sweden
²Department of Chemistry, POSTECH, Pohang 37673, Republic of Korea
³Department of Molecular Sciences and Nanosystems, Ca’ Foscari University of Venice, 30172 Venice-Mestre, Italy
⁴Department of Environmental Science and Bolin Centre for Climate Research, Stockholm University, 114 18 Stockholm, Sweden
⁵Biomedical and X-Ray Physics, Department of Applied Physics, AlbaNova University Center, KTH Royal Institute of Technology, SE-10691 Stockholm, Sweden
⁶Molecular Biophysics and Integrated Bioimaging Division, Lawrence Berkeley National Laboratory, Berkeley, CA 94720, USA
⁷Department of Cell and Molecular Biology, Laboratory of Molecular Biophysics, Uppsala University, SE-75124 Uppsala, Sweden
⁸Department of Chemistry, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA
⁹SLAC National Accelerator Laboratory, Menlo Park, California 94025, USA
¹⁰Japan Synchrotron Radiation Research Institute, Kouto 1-1-1, Sayo, Hyogo 679-5198, Japan
¹¹Institute for Solid State Physics, The University of Tokyo, Kouto 1-1-1, Sayo, Hyogo 679-5148, Japan

^*kimkyunghwan@postech.ac.kr
^†f.perakis@fysiks.su.se

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Issue

Vol. 125, Iss. 7 — 14 August 2020

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Images

Figure 1
The experimental setup using anisotropic x-ray scattering under OKE condition. The alignment of liquid water is triggered by a linearly polarized optical laser pulse. Subsequently, a time-delayed x-ray pulse probes the anisotropy decay, obtained by subtracting the perpendicular ( $S_{⊥}$ ) from the parallel ( $S_{∥}$ ) scattering pattern.
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Figure 2
(a) Experimental difference scattering curves for anisotropy (left, $S_{∥} − S_{⊥}$ ) and heating (right, $S_{laser_on} − S_{laser_off}$ ) measured at four different time delays at 298 K. (b) Time-dependent changes of anisotropy (top) and heating (bottom) and the corresponding fits. The anisotropy decays biexponentially with the relaxation time of $\sim 160 fs$ and 1 ps and the heating signal increases with the timescale of $\sim 1 ps$ . The four delay points shown in (a) are indicated with blue dashed lines.
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Figure 3
MD simulation of the transiently oriented water and the comparison with the experimental results. (a) Difference scattering curve for anisotropy calculated from MD simulations at 50 fs after the external electric field (red line) is compared with the experiment (black square). (b) Time-dependent $⟨ \cos^{2} (θ) ⟩ - ⅓$ of water molecules in the simulation (blue solid line) is compared with the experimental time-dependent anisotropy (open circle). The angle $θ$ is the angle between the dipole of the water molecule and the polarization of the external electric field. When $⟨ \cos^{2} (θ) ⟩ - ⅓$ is convoluted with the instrument response function ( $\sim 210 fs$ ), it exhibits qualitatively good agreement with the experiment. (c),(d) The O-O radial distribution functions calculated from the MD at $- 1 ps$ (solid black line), 50 fs (dashed red line), and 2 ps (dotted blue line) are compared at the first peak (c) and the second peak (d). (Insets) The difference signals.
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Figure 4
LSI-dependent analysis. (a) Time-dependent $⟨ \cos^{2} (θ) ⟩ - ⅓$ of HDL species (red) and LDL species (blue) are shown. The LDL species are more susceptible to alignment than HDL species, indicated by the higher amplitude. (b) Difference between the averaged oxygen-oxygen partial radial distribution functions for the time range from 0.0 to 0.5 ps and the reference ( $- 1$ to $- 0.5 ps$ ) for the HDL and LDL species. Again here, the LDL species are affected more by the electric field than HDL species, indicated by larger difference signal. (Inset) Details of the curves at larger distances.
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