UNRAVELING THE INTENSITY PATTERNS IN THE INFRARED SPECTRA OF X$^-$($^{1,2}$HO$^{1,2}$H) [X=F,Cl]
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Date
2007
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Ohio State University
Abstract
The distortions from equilibrium and changes in the infrared spectra of a single water molecule when it is complexed with a halide ion (F$^-$, Cl$^-$, and Br$^-$) have been of great interest for the past several years.}}, 7688 (2005).}$^,$}}, 571 (2005).} In these systems the bonded hydrogen stretch ($\nu_2$), the so-called ``proton-transfer'' mode, as well as the in-plane ($\nu_4$) and the out-of-plane ($\nu_6$) bending modes have displayed unexpected intensity patterns in the experimental infrared spectra.}}, 4943 (2006).} An example of such anomalies can be seen in the $\nu_2$ mode of F$^-$(H$_2$O). This vibrational mode exhibits significant intensity in the fundamental transition, over ten times that of any other fundamental, and its frequency is shifted by nearly 1500 cm$^{-1}$ to the red of the free OH stretch. Analysis of the first and second overtones in $\nu_2$ indicates that anharmonicity is not as significant as one might expect from such a large redshift of the fundamental.\newline\newline We investigate the underlying motions associated with the $\nu_2$, $\nu_4$, and $\nu_6$ modes by calculating the potential energy and dipole moment surfaces at the MP2 level of theory using aug-cc-pVTZ basis sets. The X$^-$(H$_2$O) vibrational energies and wave functions are determined using one- and two-dimensional}}, 1982 (1992).} variational calculations. Our theoretical results reproduce the experimental findings extremely well and provide insight into the physics behind these intriguing spectral features.
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Author Institution: Department of Chemistry, The Ohio State University, Columbus, OH 43210