Knowledge Bank

The equilibrium geometries of halide-water complexes, $X-(H2O)n$, have, to date, not been determined conclusively. We have obtained infrared spectra of $Cl-(H2O)n(n=1-5)$ that, in conjunction with ab initio calculations, give us some ability to predict likely optimal strctures. For $Cl-(H2O)$, the observation of an intense band at $3285cm-1$ is evidence that water forms one nearly-linear hydrogen bond to chloride. For $Cl(H2O)2$, we observed two intense bands at $3245cm-1$ and $3317cm-1$, but saw no band in the $3500-3650cm-1$ 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.