Experimental determination of structural motifs of interference-free water undecamer cluster (H<sub>2</sub>O)<sub>11</sub>.
basic_science · Level V
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- Record sourced from PubMed, PMID 41390762.
- Also identified by DOI 10.1038/s41467-025-66717-5 and PMC identifier 12748990.
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Abstract
Structural characterization of archetypal water clusters is essential for exploring the nature of aqueous hydrogen-bonding interactions that are responsible for the properties of water. While spectroscopic measurement of interference-free neutral water clusters has been proven to be challenging due to the difficulty in size selection, recent studies have successfully measured the infrared spectra of small water clusters (H<sub>2</sub>O)<sub>n</sub> (n = 2-10). Thus far, experimental evidence for structural motifs of larger water clusters (H<sub>2</sub>O)<sub>n</sub> (n ≥ 11) without environmental perturbation such as an ultraviolet-chromophore label, a messenger tag, or a host matrix has been lacking. Here utilizing the recently-developed size-specific infrared spectroscopy apparatus with a tunable vacuum ultraviolet free electron laser (VUV-FEL) and quantum-chemical studies, we have provided experimental evidence to characterize the structure of interference-free neutral water undecamer (H<sub>2</sub>O)<sub>11</sub>. Distinct OH stretching bands provide the evidence for the three lowest-energy isomer families denoted as 515, 43'4, and 55'1 structural motifs. The 515 structure is found to be the dominant one, which features a "5 + 1 + 5" assembling of two stacked 5-membered rings with an additional H<sub>2</sub>O on the side. Formation mechanism of these three structural motifs is proposed based on calculated energetics. This work provides crucial insights into the microscopic development of hydrogen-bonding water networks and advances our capabilities toward size-dependence study of a diverse range of neutral hydrated clusters for exploring the stepwise mechanisms of solvation processes such as salt dissolution and acid dissociation.