Structure and vibrational spectra of H+(HF)n (n=2-9) clusters: An ab initio study

The morphological development of the hydrogen bond network in the protonated hydrogen fluoride clusters, H+(HF)(n) (n=2-9), is investigated in detail by ab initio methods. We find a dominance of the linear morphology, which is energetically well separated from the other minimum energy morphologies of the clusters. The geometry for these clusters shows a pattern due to the cooperativity effect prevalent in the hydrogen bonds, as a result of the difference in electronegativities of hydrogen and fluorine atom in the HF molecule. The variations in the covalent HF and hydrogen bond distances in the clusters are in turn reflected in the vibrational spectra. Distinct HF stretching modes for the linear and ring with tail structures were identified. We have discussed the signature peaks for the two possible ion-core morphologies present in the clusters. The highly corrosive nature of HF makes it difficult to study using experiments. We, thus, believe that our structure and vibrational spectra calculations would be useful in understanding the key features in these systems.