Hydrogen transitions between (HF)n Cnh structures (n=2−5) via Dnh transition states as models for hydrogen tunneling in hydrogen fluoride clusters

In order to obtain a realistic model of hydrogen tunneling in hydrogen fluoride clusters, a concerted transfer of hydrogens comparable to the well-known Grotthus mechanism discussed for the hydrogen transfer in water was investigated. Hydrogen tunneling barriers between two Cnh clusters (mirror images) were calculated at the MP2 level of theory with a 6-311++G(3df, 3pd) basis set. The corresponding A′ (respectively Ag) tunneling frequencies of the Cnh structures and the force constants in the direction corresponding to A1′ and A2′ (respectively A1g and A2g, Ag and B1g) in the related Dnh barrier structures were investigated to estimate the shape of the tunneling path.