Planar clusters of Rydberg matter KN (N=7, 14, 19, 37, 61) detected by multiphoton fragmentation time-of-flight mass spectrometry

We report a direct observation of large planar clusters characteristic for Rydberg matter. This state of matter has low density with interatomic distances of the order of tens of nanometers. We observe the laser multiphoton-induced fragmentation and ionization of potassium clusters KN+ with N (the magic numbers) =7, 14, 19, 37 and 61 in processes due to 5–12 photons of 2.2 eV (564 nm) in 5 ns pulses, using time-of-flight (TOF) mass spectrometry. The clusters are formed by desorption of K* Rydberg atoms from a basal graphite surface, which is intercalated by a weak molecular beam of K. The fragmentation is strongly influenced by the electric field used, below 4 V/cm. The efficient multiphoton fragmentation is probably due to the low rate of E–V transfer in the cluster.