Hydrogen Bonds in Solid Hydrates of Aqueous Salts studied by
Quantum Simulations and Sub-picosecond Infrared Spectroscopy
EMSL Project ID
37507
Abstract
Solid hydrates of salts containing a fixed ratio of water molecules in their crystal structures have attracted special interest due to their importance in geology, chemistry, and physics. The quest for deciphering the properties of hydrogen bonds makes those materials ideal candidates for studying the spectral signatures of water in different, well-defined environments with varying bonding partners and distances. Organic salts and several gases are also capable of forming hydrates, the latter category being the subject of intensive investigation lately. Several efforts have previously aimed in predicting the properties of hydrates from simple thermodynamic parameters of the binary components, namely the corresponding salt and water. Frenkel characterized the water in hydrates to be in an 'ice-like' state, and this expression has henceforth been used to qualitatively describe the state of the water molecules in the hydrate crystal. Dunitz suggested that each water molecule in the hydrate contributes on average the same amount to the standard entropy, this amount being roughly equal to the standard entropy of ice at its freezing point. Of special interest is the 'difference rule' suggested by Glasser and Jenkins, demonstrating that many thermodynamic properties of hydrates are additive with respect to the bound solvent. The discussion of the thermodynamic properties of hydrates is still continuing today, as some salt hydrates are harder to form than others and others do not form at all. Many salt hydrates can easily be formed at ambient conditions, but oftentimes the aqueous solution has to be cooled considerably to enable hydrate formation. In fact, the formation of a given hydrate from the corresponding aqueous salt solution can be quite challenging, and the literature to this day lacks predictions on whether a given salt will form a stable hydrate or not.We propose to investigate the ability of aqueous salt solutions to form hydrates by a joint experimental-theoretical effort. The experimental approach, which will be carried out at the Physics Department of the Technical University of Munich at Garching, will be based on infrared (IR) spectroscopy whereas the theoretical part that will be used to calculate the IR spectra from first principles Born-Oppenheimer Molecular Dynamics (BOMD) simulations and therefore assign the underlying structures of the salt hydrates, will be performed using the resources of the High-Performance Computing Center at EMSL. To this end, we have performed preliminary experiments and simulations for the NaCl dihydrate in order to indicate the synergy between experimental and theoretical approaches towards understanding the nature of hydrogen bonding in aqueous salt hydrates.
Project Details
Project type
Exploratory Research
Start Date
2009-12-02
End Date
2010-12-05
Status
Closed
Released Data Link
Team
Principal Investigator
Team Members