Dresden 2011 – wissenschaftliches Programm
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MO: Fachverband Molekülphysik
MO 7: Poster: Cluster
MO 7.2: Poster
Montag, 14. März 2011, 16:00–18:00, P1
Melting of size-selected, free water clusters — •Adam Piechaczek, Christian Hock, Raphael Kuhnen, Martin Schmidt, and Bernd v.Issendorff — Fakultät für Mathematik und Physik, Universität Freiburg, Stefan-Meier Str.19, 79104 Freiburg
An experimental study on free, size-selected water clusters has been performed. Negatively charged water clusters are thermalized in a temperature controlled radio frequency multipole trap by collisions with helium buffer gas at a pressure of about 10−3 mbar, transferred into high vacuum, mass-selected, and photofragmented by a laser pulse (1064 nm). The recorded fragment mass spectra are sensitive to the inner energy of the thermalized clusters, which allows us to link temperature and energy and deduce caloric curves. The curves are bulklike at low temperatures, demonstrating that the vibrational density of states of the clusters is similar to that of bulk ice. At particle-size specific temperatures, a sudden increase of the heat capacity occurs, which marks the onset of a gradual melting transition. Above the transition temperatures the caloric curves bend upwards and deviate significantly from that of the bulk. Recently the caloric curves have been measured for a wide range of cluster sizes. A strong size dependence of the melting temperature has been observed.
[1] C. Hock et al., Physical Review Letters 103, 073401 (2009)