Infrared spectroscopy of large protonated water clusters H+(H2O)20–50 cooled by inert gas attachment

Abstract

We report infrared spectra of protonated water clusters H+(H2O)n (n=20–50) cooled by H2 tagging. IR spectra show sharper features, validating the cooling effect of the H2 attachment even for the large clusters. Furthermore, the H2–mediated spectrum has indicated the origin of the first antimagic number (n=22), which is a dangling water molecule on the cluster surface [K. Mizuse, A. Fujii, J. Phys. Chem. Lett. 2 (2011) 2130]. On the other hand, for the second magic (n=28) and antimagic (n=29) number clusters, no apparent difference is observed by the H2 tagging. IR spectra of Ar-tagged H+(H2O)20–22 are also measured. These spectra also show sharper features, however, no signature for the dangling water molecule is seen in n=22. This result implies there are multiple isomer types in the n=22 cluster and the observable type might vary with the choice of the inert gas for tagging.