Inter and intramolecular interactions and rotational tunneling of methyl groups in tetramethyltin J. Chem. Phys. 94, 1765 (1991); 10.1063/1.459950The intramolecular potential of water molecules engaged in hydrogen bonding from analysis of the overtone spectrum of ice I
Using a simple one-dimensional model of H bonds, vibrational-energy eigenvalues, eigenfunctions, transition moments, and absorption intensities are calculated for a series of symmetric and asymmetric double-minimum (D.M.) potentials. On the basis of the results obtained, the necessary requirements for observing doublets in the infrared spectra of H-bonded solids are given. In most cases an asymmetric D.M. potential does not give rise to such doublets. Attention is drawn to the rapid ``switch-over'' from even-odd, odd-even to ``left-left,'' ``right-right'' selection rules when a slight asymmetry is introduced into a symmetric D.M. potential. Also, a very rapid uncoupling of resonance interaction between accidentally coincident ``left'' and ``right'' levels of strongly asymmetric D.M. potentials is predicted. The importance of obtaining accurate relative intensity values and of determining the infrared and Raman spectra of both the H-bonded solids and their deuterated analogs at several temperatures is emphasized.
Photoelectric Raman spectra of HDO in 5-mole % isotopically substituted water show single, broad, slightly asymmetric bands in both of the regions containing the uncoupled fundamental stretching motions. An empirical correlation between O–H or O—D stretching frequency and O···O hydrogen-bonded distance has been used to map the frequency coordinate of the spectra onto an intermolecular distance scale, and the Raman bands are replotted on this abscissa. The resulting intermolecular distribution functions for liquid water agree with x-ray results and support the suggestion that the breadth of the HDO uncoupled stretching bands reflects the variation of intermolecular distance. Moreover, it is noted that the corresponding infrared and Raman bands are almost superposable, and that this indicates little hydrogen-bond breakage in liquid water. The distribution of intermolecular distances represented by the spectra is compared to that incorporated in some of the structural models for liquid water. It appears that a successful model should incorporate the homogeneity, isotropy, coherence, and disorder of the liquid in its local structure.
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