Spectroscopic snapshot for neutral water nonamer (H2O)9: Adding a H2O onto a hydrogen bond-unbroken edge of (H2O)8

Structural characterization of neutral water clusters is crucial to understanding the structures and properties of water, but it has been proven to be a challenging experimental target due to the difficulty in size selection. Here, we report the size-specific infrared spectra of confinement-free neutral water nonamer (H2O)(9) based on threshold photoionization, using a tunable vacuum ultraviolet free-electron laser. Distinct OH stretch vibrational fundamentals in the 3200-3350 cm(-1) region are observed, providing unique spectral signatures for the formation of an unprecedented (H2O)(9) structure evolved by adding a ninth water molecule onto a hydrogen bond-unbroken edge of the (H2O)(8) octamer with D-2d symmetry. This nonamer structure coexists with the five previously identified structures that can be viewed as derived by inserting a ninth water molecule into a hydrogen bond-broken edge of the D-2d/S-4 octamer. These findings provide key microscopic information for systematic understanding of the formation and growth mechanism of dynamical hydrogen-bonding networks that are responsible for the structure and properties of condensed-phase water.

Automated summary

In this study, size-specific infrared spectra of neutral water nonamer (H2O)9 were obtained using threshold photoionization and a tunable vacuum ultraviolet free-electron laser. The spectra revealed distinctive OH stretch vibrational fundamentals, providing unique spectral signatures for the formation of an unprecedented (H2O)9 structure. This structure coexists with five previously identified structures, shedding light on the formation and growth mechanism of hydrogen-bonding networks in condensed-phase water.