Theoretical Estimates of the IR Spectrum of Water Intercalated Into Kaolinite

Calculations at AM1, PM3, and HF/6-31G levels of part of the IR spectrum of the water-kaolinite intercalated system based on a 96-atom cluster of kaolinite with one water molecule are reported. Only the water molecule conformation is optimized. Frequencies and intensities for just the water vibrations and stretchings of four cluster hydroxyls were calculated through partial Hessian matrices and polar tensors obtained by numerical differentiation of energy gradients and dipole moment. The water molecule Was found to attach to the cluster mainly through a double hydrogen bond to the siloxane inner surface, partially entering the siloxane ring hexagonal hole. Though the theoretical results predict that the water OH stretching frequencies decrease from the gas-phase state to the intercalated state, they are stilt higher than expected with respect to the observed spectrum. (C) 2008 Wiley Periodicals, Inc. Int J Quantum Chem 109: 594-604, 2009