VIBRATIONAL PREDISSOCIATION SPECTROSCOPY OF $CI (H_{2}O)_{n} (n= 1-5)$,

Abstract

The equilibrium geometries of halide-water complexes, $X^{-}(H_{2}O)_{n}$, have, to date, not been determined conclusively. We have obtained infrared spectra of $Cl^{-} (H_{2}O)_{n} (n= 1-5)$ that, in conjunction with ab initio calculations, give us some ability to predict likely optimal strctures. For $Cl^{-} (H_{2}O)$, the observation of an intense band at $3285 cm^{-1}$ is evidence that water forms one nearly-linear hydrogen bond to chloride. For $Cl (H_{2}O)_{2}$, we observed two intense bands at $3245 cm^{-1}$ and $3317 cm^{-1}$, but saw no band in the $3500-3650 cm^{-1}$ region. This suggests that in the n = 2 cluster, both waters bind strongly to chloride ion, but not to each other. The complexity of the spectra for n=3-5 suggests that a mixture of structural isomers may have been present in our supersonic beam.