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Diffraction and IR/Raman data do not prove tetrahedral water

M Leetmaa ; K T Wikfeldt ; M P Ljungberg ; M. Odelius ; Jan Swenson (Institutionen för teknisk fysik, Kondenserade materiens fysik) ; A. Nilsson ; L G M Pettersson
Journal of Chemical Physics Vol. 129 (2008), 8, p. 084502.
[Artikel, refereegranskad vetenskaplig]

We use the reverse Monte Carlo modeling technique to fit two extreme structure models for water to available x-ray and neutron diffraction data in q space as well as to the electric field distribution as a representation of the OH stretch Raman spectrum of dilue HOD in D2O; the internal geometries were fitted to a quantum distribution. Forcing the fit to maximize the number of hydrogen (H) bonds results in a tetrahedral model with 74% double H-bond donors (DD) and 21% single donors (SD). Maximizing instead the number of SD species gives 81% SD and 18% DD, while still reproducing the experimental data and losing only 0.7-1.8 kJ/mole interaction energy. By decomposing the simulated Raman spectrum we can relate the models to the observed ultrafast frequency shifts in recent pump-probe measurements. Within the tetrahedral DD structure model the assumed connection between spectrum position and H-bonding indicates ultrafast dynamics in terms of breaking and reforming H bonds while in the strongly distorted model the observed frequency shifts do not necessarily imply H-bond changes. Both pictures are equally valid based on present diffraction and vibrational experimental data. There is thus no strict proof of tetrahedral water based on these data. We also note that the tetrahedral structure model must, to fit diffraction data, be less structured than most models obtained from molecular dynamics simulations. © 2008 American Institute of Physics.



Denna post skapades 2008-12-09. Senast ändrad 2016-07-21.
CPL Pubid: 80773

 

Institutioner (Chalmers)

Institutionen för teknisk fysik, Kondenserade materiens fysik (1900-2015)

Ämnesområden

Fysik
Den kondenserade materiens fysik
Vätskefysik

Chalmers infrastruktur