Knowledge Bank

Water clusters (H$2$O) in the range $n$ = 1 -- 30 have been studied in helium droplets. Spectral bands of clusters with $n$ = 1 -- 6 are observed and infrared intensities of water dimers, trimers and tetramers relative to that of $\nu$$3$ band of H$2$O molecule have been determined. We found non-additive enhancement of the IR intensity in water clusters, which can be used as a probe for cooperative effects. Gradual transformation of the spectrum from a relatively narrow band of small clusters to a broad spectrum, characteristic for a bulk ice, is observed.