Coherent X-rays reveal the influence of cage effects on ultrafast water dynamics

• DOI: 10.1038/s41467-018-04330-5
• Publication Date: 2018-05-09T10:37:50Z
• Authors: Fivos Perakis; Gaia Camisasca; Thomas J. Lane; Alexander Späh; Kjartan Thor Wikf...; Jonas A. Sellberg; Felix Lehmkühler; Harshad Pathak; Kyung Hwan Kim; Katrin Amann-Winkel; Simon Schreck; Sanghoon Song; Takahiro Sato; Marcin Sikorski; Andre Eilert; Trevor McQueen; Hirohito Ogasawara; Dennis Nordlund; Wojciech Roseker; Jake Koralek; Silke Nelson; Philip Hart; Roberto Alonso-Mori; Yiping Feng; Diling Zhu; Aymeric Robert; Gerhard Grübel; Lars G. M. Petter...; Anders Nilsson
• Keywords: LIQUID WATER; 0303 health sciences; Science; Q; 500; DIFFRACTION; Article; TIME; TIP4P/2005; 03 medical and health sciences; FREE-ELECTRON LASER; MOLECULAR-DYNAMICS; 13. Climate action; SPECKLE-VISIBILITY SPECTROSCOPY; SCATTERING; PHOTON-CORRELATION SPECTROSCOPY; AMBIENT; info:eu-repo/classification/ddc/500

AbstractThe dynamics of liquid water feature a variety of time scales, ranging from extremely fast ballistic-like thermal motion, to slower molecular diffusion and hydrogen-bond rearrangements. Here, we utilize coherent X-ray pulses to investigate the sub-100 fs equilibrium dynamics of water from ambient conditions down to supercooled temperatures. This novel approach utilizes the inherent capability of X-ray speckle visibility spectroscopy to measure equilibrium intermolecular dynamics with lengthscale selectivity, by measuring oxygen motion in momentum space. The observed decay of the speckle contrast at the first diffraction peak, which reflects tetrahedral coordination, is attributed to motion on a molecular scale within the first 120 fs. Through comparison with molecular dynamics simulations, we conclude that the slowing down upon cooling from 328 K down to 253 K is not due to simple thermal ballistic-like motion, but that cage effects play an important role even on timescales over 25 fs due to hydrogen-bonding.