QUANTITATIVE AB INITIO PREDICTION OF THE VIBRATIONAL SPECTRA OF INTERACTING PAIRS OF WATER $MOLECULES^{\ast}$
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Date
1982
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Ohio State University
Abstract
Infrared spectra of hydrogen banded species are characterized by frequency shifts and intensity changes from the corresponding monomer vibration. The water dimer is the simplest model system for detailed studies leading to understanding of the vibrational spectroscopic properties of hydrogen-bonded species. The water dimer is believed to be most stable in the linear form, but cyclic and bifurcated structures have also been considered. We have used 4-31G basis functions with the Gaussian 76 program to carry out ab initio quantum-mechanical calculations of the energies and dipole moments of water dimers as a function of vibrational displacements. The displacements are made in a molecule-fixed cartesian coordinate system and the results are analyzed to obtain force constants and intensity parameters (atomic polar tensors). These are then used to predict the frequency and the intensity for each of the vibrations of water monomer and of water dimers. The resulting predicted spectra are compared with each other and with experimental studies of the spectra of water isolated in inert matrices. Predictions for water pairs in different conformations and for different distances of interaction provide both qualitative and quantitative insight into the nature of vibrational spectral changes occurring when molecules interact, including for example, indications of which effects are due to charge transfer in hydrogen bond formation, and which are due only to static and dynamic charges and charge polarizations, Predictions of the infrared spectrum of isolated $H_{3}O^{+}$ ions are also presented.
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$^{\ast}$Support from the National Science Foundation Grant No. CHESI-01131 is gratefully acknowledged.