Rotational dynamics in supercooled water from nuclear spin relaxation and molecular simulations.
(2012) In Journal of Chemical Physics 136(20). Abstract
 Structural dynamics in liquid water slow down dramatically in the supercooled regime. To shed further light on the origin of this superArrhenius temperature dependence, we report highprecision (17)O and (2)H NMR relaxation data for H(2)O and D(2)O, respectively, down to 37 K below the equilibrium freezing point. With the aid of molecular dynamics (MD) simulations, we provide a detailed analysis of the rotational motions probed by the NMR experiments. The NMRderived rotational correlation time τ(R) is the integral of a time correlation function (TCF) that, after a subpicosecond librational decay, can be described as a sum of two exponentials. Using a coarsegraining algorithm to map the MD trajectory on a continuoustime random walk... (More)
 Structural dynamics in liquid water slow down dramatically in the supercooled regime. To shed further light on the origin of this superArrhenius temperature dependence, we report highprecision (17)O and (2)H NMR relaxation data for H(2)O and D(2)O, respectively, down to 37 K below the equilibrium freezing point. With the aid of molecular dynamics (MD) simulations, we provide a detailed analysis of the rotational motions probed by the NMR experiments. The NMRderived rotational correlation time τ(R) is the integral of a time correlation function (TCF) that, after a subpicosecond librational decay, can be described as a sum of two exponentials. Using a coarsegraining algorithm to map the MD trajectory on a continuoustime random walk (CTRW) in angular space, we show that the slowest TCF component can be attributed to largeangle molecular jumps. The mean jump angle is ∼48° at all temperatures and the waiting time distribution is nonexponential, implying dynamical heterogeneity. We have previously used an analogous CTRW model to analyze quasielastic neutron scattering data from supercooled water. Although the translational and rotational waiting times are of similar magnitude, most translational jumps are not synchronized with a rotational jump of the same molecule. The rotational waiting time has a stronger temperature dependence than the translation one, consistent with the strong increase of the experimentally derived product τ(R) D(T) at low temperatures. The present CTRW jump model is related to, but differs in essential ways from the extended jump model proposed by Laage and coworkers. Our analysis traces the superArrhenius temperature dependence of τ(R) to the rotational waiting time. We present arguments against interpreting this temperature dependence in terms of modecoupling theory or in terms of mixture models of water structure. (Less)
Please use this url to cite or link to this publication:
http://lup.lub.lu.se/record/2859801
 author
 Qvist, Johan ^{LU} ; Mattea, Carlos ^{LU} ; Persson Sunde, Erik ^{LU} and Halle, Bertil ^{LU}
 organization
 publishing date
 2012
 type
 Contribution to journal
 publication status
 published
 subject
 in
 Journal of Chemical Physics
 volume
 136
 issue
 20
 publisher
 American Institute of Physics
 external identifiers

 wos:000304818400037
 pmid:22667569
 scopus:84862527001
 ISSN
 00219606
 DOI
 10.1063/1.4720941
 language
 English
 LU publication?
 yes
 id
 cedc62777f2541e4969c83512ad9fdc6 (old id 2859801)
 date added to LUP
 20120713 12:45:21
 date last changed
 20170820 03:02:46
@article{cedc62777f2541e4969c83512ad9fdc6, abstract = {Structural dynamics in liquid water slow down dramatically in the supercooled regime. To shed further light on the origin of this superArrhenius temperature dependence, we report highprecision (17)O and (2)H NMR relaxation data for H(2)O and D(2)O, respectively, down to 37 K below the equilibrium freezing point. With the aid of molecular dynamics (MD) simulations, we provide a detailed analysis of the rotational motions probed by the NMR experiments. The NMRderived rotational correlation time τ(R) is the integral of a time correlation function (TCF) that, after a subpicosecond librational decay, can be described as a sum of two exponentials. Using a coarsegraining algorithm to map the MD trajectory on a continuoustime random walk (CTRW) in angular space, we show that the slowest TCF component can be attributed to largeangle molecular jumps. The mean jump angle is ∼48° at all temperatures and the waiting time distribution is nonexponential, implying dynamical heterogeneity. We have previously used an analogous CTRW model to analyze quasielastic neutron scattering data from supercooled water. Although the translational and rotational waiting times are of similar magnitude, most translational jumps are not synchronized with a rotational jump of the same molecule. The rotational waiting time has a stronger temperature dependence than the translation one, consistent with the strong increase of the experimentally derived product τ(R) D(T) at low temperatures. The present CTRW jump model is related to, but differs in essential ways from the extended jump model proposed by Laage and coworkers. Our analysis traces the superArrhenius temperature dependence of τ(R) to the rotational waiting time. We present arguments against interpreting this temperature dependence in terms of modecoupling theory or in terms of mixture models of water structure.}, articleno = {204505}, author = {Qvist, Johan and Mattea, Carlos and Persson Sunde, Erik and Halle, Bertil}, issn = {00219606}, language = {eng}, number = {20}, publisher = {American Institute of Physics}, series = {Journal of Chemical Physics}, title = {Rotational dynamics in supercooled water from nuclear spin relaxation and molecular simulations.}, url = {http://dx.doi.org/10.1063/1.4720941}, volume = {136}, year = {2012}, }