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

We report infrared spectra of protonated water clusters H+(H2O)(n) (n = 20-50) cooled by H-2 tagging. IR spectra show sharper features, validating the cooling effect of the H-2 attachment even for the large clusters. Furthermore, the H-2-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 H-2 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. (C) 2012 Elsevier B. V. All rights reserved.