Professor Dr. Frédéric Merkt Laboratorium für Physikalische Chemie Einladung zu einem Seminar über Theoretische Chemie, Molekülspektroskopie und Dynamik Referent: Professor Thomas F. Gallagher Department of Physics University of Virginia, Charlottesville Thema: Dipole-Dipole Interactions of Rydberg Atoms Ort: HCI J 6 Datum/Zeit: Freitag, 7. März, 2008 16:45 Uhr At room temperature and down to 1 K dipole-dipole interactions in Rydberg atoms are most clearly manifested in binary resonant energy transfer collisions, which have enormous cross sections and long temporal durations. Since both the cross sections and the durations of the collisions increase with decreasing temperature, one might expect to observe even larger cross sections and longer collision times if the cold atoms in a magneto optical trap (MOT) are excited. While this is true, the high density of Rydberg atoms allowed by the MOT opens the way to a new regime in which the atoms are, on an experimentally interesting time scale, nearly frozen in place. An atom can interact with many atoms at the same time, so energy transfer in the frozen Rydberg gas is more like an amorphous solid than a conventional gas. The dipole-dipole interaction also leads to ionization of the initially frozen Rydberg gas. It occurs by a many-body form of molecular autoionization, roughly the bound-continuum analog of the bound-bound energy transfer mentioned above, and by motion of the atoms along attractive dipole-dipole potentials. Both of these processes play a role in the spontaneous evolution of the frozen Rydberg gas into an ultracold plasma. Gäste sind willkommen Prof. Frédéric Merkt Prof. Martin Quack Prof. Markus Reiher
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