Infrared detection of (H₂O)₂₀ isomers of exceptional stability: a drop-like and a face-sharing pentagonal prism cluster

Abstract

Water clusters with internally solvated water molecules are widespread models that mimic the local environment of the condensed phase. The appearance of stable (H2O)n cluster isomers having a fully coordinated interior molecule has been theoretically predicted to occur around the n = 20 size range. However, our current knowledge about the size regime in which those structures become energetically more stable has remained hypothetical from simulations in lieu of the absence of precisely size-resolved experimental measurements. Here we report size and isomer selective infrared (IR) spectra of (H2O)20 clusters tagged with a sodium atom by employing IR excitation modulated photoionization spectroscopy. The observed absorption patterns in the OH stretching region are consistent with the theoretically predicted spectra of two structurally distinct isomers of exceptional stability: a drop-like cluster with a fully coordinated (interior) water molecule and an edge-sharing pentagonal prism cluster in which all atoms are on the surface. The drop-like structure is the first experimentally detected water cluster exhibiting the local connectivity found in liquid water.

The temperature and size distribution of large water clusters from a non-equilibrium model

“…[34][35][36][37] We detected by their characteristic absorption pattern in the OH stretching region two cluster isomers of exceptional stability, a pentagonal edge sharing prism (isomer A) and a drop-like cluster (isomer B) with an internally solvated water molecule. 38 The two isomers are shown in Fig. 9.…”

Accurate vibrational spectra via molecular tailoring approach: A case study of water clusters at MP2 level

“…Out of these, intramolecular O-H stretching region serves as the "fingerprint" region and displays distinctively different features for the HB networks. 4,7 The current study concentrates on both bending and stretching regions. The antiboat isomer contains either tetra-coordinated (DDAA) or tri-coordinated water molecules (DDA and DAA type water molecules, where D = proton donor and A = proton acceptor) connected through a total of 26 HBs.…”

“…3 Several studies, reporting the theoretically calculated vibrational spectra of a variety of molecular clusters, are available in the literature. [4][5][6][7][8][9][10][11][12][13] Among these, most of the investigations are reported on water clusters. Xantheas and coworkers [4][5][6][7] have explored the energetics and vibrational spectra of water clusters of various sizes, during the last decade.…”

“…[4][5][6][7][8][9][10][11][12][13] Among these, most of the investigations are reported on water clusters. Xantheas and coworkers [4][5][6][7] have explored the energetics and vibrational spectra of water clusters of various sizes, during the last decade. Vibrational signatures of different hydrogen bond (HB) networks of small-sized (H 2 O) 6 to large-sized (H 2 O) 20 clusters have been analyzed at Møller-Plesset second order (MP2) level of theory.…”

Nanometer patterning of water by tetraanionic ferrocyanide stabilized in aqueous nanodrops

“…Water molecules at the surface of neutral clusters are free to orient with non-bonded hydrogens facing away from the cluster, which has been observed experimentally by the unique absorption band at ∼3700 cm –1 . 37,38 Using IRPD spectroscopy of mass-selected, ion-containing water clusters, orientation effects on water by a single solvated ion free of any counterion contributions can be measured. 21,39,40 The sensitivity of this technique is not limited by the ratio of water molecules to ions.…”