Geometry of the magic number H + ( H 2 O ) 21 water cluster by proxy † Mauritz

Abundance mass spectra, obtained upon carefully electrospraying solutions of tert-butanol (TB) in water into a mass spectrometer, display a systematic series of peaks due to mixed H(TB)m(H2O)n clusters. Clusters with m + n = 21 have higher abundance (magic number peaks) than their neighbours when m r 9, while for m 4 9 they have lower abundance. This indicates that the mixed TB–H2O clusters retain a core hydrogen bonded network analogous to that in the famous all-water H(H2O)21 cluster up to the limit m = 9. The limiting value corresponds to the number of dangling O–H groups pointing out from the surface of the degenerated pentagonal dodecahedral, considered to be the lowest energy form of H(H2O)21; the experimental findings therefore support this geometry. The experimental findings are supported by ab initio quantum chemical calculations to provide a consistent framework for the interpretation of these kinds of experiments.