Isomerization and melting-like transition of size-selected water nonamers

The vibrational OH-stretch spectra of size-selected pure water (H(2)O)(9) clusters, measured at two different temperatures, have been used to identify isomeric transitions. The broad, featureless high-temperature, liquid-like spectrum resembles that of water, while the structured low- temperature, solid-like spectrum differs appreciably from that of ice. Accompanying calculations suggest that the low-temperature spectra originate from two cube-like structures. The high-temperature spectra appear to be above an isomeric transition to more open amorphous arrangements of fused three- to five-membered rings.