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Gamma and conversion electron radiations following the decay of 1.7 s 123mC~ and 5.9 min lZsCs have been studied in singles and coincidence with mass-separated sources at the ISOLDE facility. Evidence for a 61.7 keV E3 transition, de-exciting the yisomeric state of I2ks, has been found. A scheme for the 123Cs ground-state decay including 11 new low-spin levels has been constructed. Log ff values have been calculated; limits on possible spins are deduced which invalidate in particular the previous J = { assignment for the 180.6 keV level in '"Xe. The results are discussed in the frame of odd-mass neutrondeficient Cs and Xe systematics. RADIOACTIVITY 123mC~, 123Cs (from La(p, 3p14n)), E,= 600 MeV, on-line massseparated sources; measured T1/2, E,, I,, E,, I,, yy coin, y ce coin; L23Cs, L23Xe; deduced levels, J , n, log fl. Ge(Li), Si(Li) and plastic detectors.

The structures and stabilities of the van der Waals clusters (N 2 ) n (n = 2-8) have been evaluated using ab initio calculations at the MP2(full)/6 311+G* and CCSD(full)/6 311+G* level of theory. At n = 2-4, the formation of planar and three dimensional structures is possible. At n > 4, only "globular" structures can be formed, whose formation energies increase with the cluster size. As the number of interacting molecules increases, the examined systems exhibit cooperative effects associated with non additive enhancement of nonbonded intermo lecular interactions.Key words: nitrogen clusters, nonbonded interactions, cooperative effects, ab initio quan tum chemical calculations, MP2(full)/6 311+G* method, CCSD(full)/6 311+G* method.Recently, the van der Waals complexes formed by means of weak long range intermolecular forces and be ing at the edge of stable systems have been attracting an increased attention of experimentalists and theorists.

Positive DC breakdown voltages of various NZ-02 gas mixtures have been measured with point-to-plane gaps over a temperature range 293 K-113 K, the gas density being kept constant at any temperature. The breakdown voltage in Nz increased at low temperatures. The increase in breakdown voltages became small, when a small amount of O Z (less than 1 %) was mixed into Nz. The breakdown voltage in synthetic air decreased at low temperatures. When small pulses were superposed on DC voltages, the breakdown voltage changes only slightly with temperature in both Nz and synthetic air.