Institut des Sciences Moléculaires d'Orsay



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Accueil > Séminaires > Année 2010 > Séminaire Klaus Muller-Dethlefs (10 juin 2010)

Séminaire Klaus Muller-Dethlefs (10 juin 2010)

The Photon Science Institute School of Chemistry - The University of Manchester Alan Turing Building U K

For ZEKE spectroscopy the experimental conditions are usually set to produce an ensemble of only weakly interacting, very high-n Rydberg states at low density (typically < 105/cm3), very far away from plasma conditions. In contrast, the formation of a Rydberg plasma by ZEKE excitation can be expected when increasing the ion/electron density. We have produced such an ultra-cold molecular Rydberg plasma with ion densities around 1015/cm3 for two molecules, para-difluorobenzene (pDFB) and nitric oxide. For NO (in Ne as carrier gas) we produce such an ultra-cold, very long lifetime Rydberg plasma by two photon excitation into the threshold region, resonant via the A-state (N=0), in the expansion region of a supersonic jet, close to the nozzle. Collisions in the jet expansion cool the ions in the plasma to ca. 0.1K thus avoiding disorder heating as in MOT Rydberg plasma experiments. After 320ms, when the plasma hits a 4mm diam. aperture, a dramatic increase in density is experimentally observed just behind this aperture. These observations can be explained by a compression of the plasma, which exhibits the properties of a sponge like material, i.e. a plasma crystal. These observations substantiate the evidence that this experimental route creates a strongly-coupled plasma with condensed phase properties. The experimental observations are consistent with the formation of a strongly-coupled, ultra-cold plasma, crystallising into a “jellium” metal-like solid, possibly a new state of matter.

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