Protonated water clusters with 60 to 79 molecules have been studied by a new option of nano calorimetry. The technique is based on multi-collision excitations of the accelerated clusters with helium. The caloric curves indicate phase transitions that resemble those of water clusters charged by an excess electron, but the transition temperatures of the protonated clusters are higher. The charging impurity in the clusters of the investigated size range seems to have a stronger influence onto the melting points than classical simulations indicate. Glass transitions temperatures of amorphous ice are close to the transitions observed in free clusters, while melting of ice in the bulk or in nanopores occurs at temperatures well above. Therefore, the relation between melting, glass transitions and continuous melting in the context of small clusters will be discussed.
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