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ZEKE Rydberg states in a crowd and "Condensed Rydberg Clusters": |
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| Klaus Muller-Dethlefs | |
| The University of Manchester | |
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We have produced an ultracold molecular Rydberg plasma by threshold ionisation in the high density region of a pulsed supersonic jet expansion close to the nozzle. In the present experiments para-difluorobenze (pDFB) was chosen because a single laser allows the excitation to Rydberg levels very close to the ionisation threshold while simultaneously being resonant with the S1¬S0 transition in the neutral molecule. The experimental results demonstrate the formation of a new giant size “Condensed Rydberg Cluster” state, which is compatible with the condensation of a number of cations n, probably at a distance of hundreds of nanometers, by a number of electrons m (m £ n) to form a collectively excited state of matter. Condensed Rydberg Clusters with mass to charge ratios (setting the mass of pDFB+º1) of 2, 3, 9 and 23 are observed. A possible interpretation of the experimental results is that the laser excitation results in the formation of a strongly coupled ultracold Rydberg plasma. Upon application of a small pulsed electric field this breaks up into CRC’s of various size and various mass to charge ratio, which are then detected according to their specific time-of-flight. Most recently we have verified CRC formation for another molecule, nitric oxide, by using two-colour, two-photon excitation to the Rydberg threshold region. For the CRC with m/e=65 we have also shown that Coulomb explosion after pulsed field ionisation leads to an NO+ kinetic energy of ca. 30 meV, corresponding to an estimated ion distance in the CRC of around hundred nm Jingwei Guo, Mervash Varnasseri, Xin Tong, Mikko Riese and Klaus Müller-Dethlefs The Photon Science Institute |