Web Release Date: June 8,
Hydration and Dissociation of Hydrogen Fluoric Acid (HF)
and
Department of Chemistry, Pai Chai University, Daejeon 302-735, Korea, Korea Institute of Science and Technology, Seoul 130-650, Korea, and Center for Supefunctional Materials, Department of Chemistry, Division of Molecular and Life Science, Pohang University of Science and Technology, Pohang 790-784, Korea
Received: January 9, 2006
In Final Form: March 19, 2006
Abstract:
The hydration and dissociation phenomena of HF(H2O)n (n 
10) clusters have been studied by using both
the density functional theory with the 6-311++G**[sp] basis set and the M
ller-Plesset second-order
perturbation theory with the aug-cc-pVDZ+(2s2p/2s) basis set. The structures for n 
8 are first reported
here. The dissociated form of the hydrogen-fluoric acid in HF(H2O)n clusters is found to be less stable at 0
K than the undissociated form until n = 10. HF may not be dissociated at 0 K solely by water molecules
because the HF H bond is stronger than the OH H bond, against the expectation that the dissociated HF(H2O)n
would be more stable than the undissociated one in the presence of a number of water molecules. The
dissociation would be possible for only a fraction of a number of hydrated HF clusters by the Boltzmann
distribution at finite temperatures. This is in sharp contrast to other hydrogen halide acids (HCl, HBr, HI)
showing the dissociation phenomena at 0 K for n 4. The IR spectra of dissociated and undissociated structures
of HF(H2O)n are compared. The structures and binding energies of HF(H2O)n are found to be similar to those
of (H2O)n+1. It is interesting that HF(H2O)n=5,6,10 are slightly less stable compared with other sizes of clusters,
just like the fact that (H2O)n=6,7,11 are slightly less stable. The present study would be useful for the experimental/spectroscopic investigation of not only the dissociation phenomena of HF but also the similarity of the HF-water clusters to the water clusters.
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