Berlin 2001 – scientific programme
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MO: Molekülphysik
MO 5: Clusters II: Non-Metal Clusters, Fullerenes, Nano-tubes (joint session A and MO)
MO 5.11: Talk
Tuesday, April 3, 2001, 18:15–18:30, H1012
Vapour Pressure Measurements of Fullerenes — •W. Kamke and R. Jaensch — Fakultät für Physik, Universität Freiburg, Hermann-Herder-Straße 3, 79104 Freiburg
For the measurement of absolute cross sections of free molecules reliable data must be available on the density of the species under study. In contrast to gaseous substances atoms and molecules of solid or liquid material are typically evaporated into the gas phase at suitable temperatures, the density being controlled by the temperature of the evaporating surface. The relation between temperature and vapor pressure or density must therefore be known precisely.
Typically, the vapor pressure is determined through measurements of mass loss or evaporation rate from Knudsen type cells. Basic Knudsen effusive conditions are generally assumed in these experiments, only corrections for the dimensions of the orifice being accounted for. A very basic problem, however, arises when large molecules like fullerenes are studied and the mean free path thus may be small compared with the dimensions of the orifice. A practical treatment of these cases ist discussed, and the results are illustrated by numerical simulations.
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