Calorimetric Observation of the Melting of Free Water Nanoparticles at Cryogenic Temperatures

Abstract

We present an experimental study of the thermodynamics of free, size-selected water cluster anions consisting of 48 and 118 molecules. The measured caloric curves of the clusters are bulklike at low temperatures but show a well-defined, particle-size specific transition at $93\ifmmode\pm\else\textpm\fi{}3\text{ }\text{ }\mathrm{K}$ for $({\mathrm{H}}_{2}\mathrm{O}{)}_{48}^{\ensuremath{-}}$ and $118\ifmmode\pm\else\textpm\fi{}3\text{ }\text{ }\mathrm{K}$ for $({\mathrm{H}}_{2}\mathrm{O}{)}_{118}^{\ensuremath{-}}$. At the transition temperature the heat capacity strongly increases, which marks the onset of melting.