We studied simultaneously the 4 He(e, e p), 4 He(e, e pp), and 4 He(e, e pn) reactions at Q 2 = 2 (GeV/c) 2 and xB > 1, for an (e, e p) missing-momentum range of 400 to 830 MeV/c. The knocked-out proton was detected in coincidence with a proton or neutron recoiling almost back to back to the missing momentum, leaving the residual A = 2 system at low excitation energy. These data were used to identify two-nucleon short-range correlated pairs and to deduce their isospin structure as a function of missing momentum, in a region where the nucleon-nucleon (N N ) force is expected to change from predominantly tensor to repulsive. The abundance of neutron-proton pairs is reduced as the nucleon momentum increases beyond ∼500 MeV/c. The extracted fraction of proton-proton pairs is small and almost independent of the missing momentum. Our data are compared with calculations of two-nucleon momentum distributions in 4 He and discussed in the context of probing the elusive repulsive N N force.

Measurements of the quenchmg rate coefficients for hydrogen atoms in the 3s 'S and 3d *D states and of oxygen atoms in the 3p 'P state by rare gases and several combustion-relevant collision partners are presented. The excited atomic states are prepared by two-photon laser excitation. Quenching cross sections for most collision partners are found to be larger than classical collision cross sections; H atoms are mostly quenched faster than 0 atoms. For the quenching of H and 0 atoms by the rare gases, the rate coefficients increase significantly with the mass of the rare gas atom.

No abstract

No abstract

Das Carbanion SF5C(CF3)2− zersetzt sich langsam zu SF5− und (CF3)2CC(CF3)2. Die Pentafluorosulfate(IV) wachsen dabei in großen Kristallen, die in Gegenwart eines SF4‐Gasdruckes längere Zeit haltbar sind. Die Kristallstrukturanalyse des Rb+SF5− (Pbnm, a = 776,1(14), b = 990,3(5), c = 614,1(3) pm, Z = 4) zeigt das SF5−‐Anion in seiner erwarteten quadratisch‐pyramidalen Struktur. Die axiale Bindung ist beträchtliche 15,9 pm kürzer als die durchschnittliche äquatoriale SF‐Bindung. Auch befindet sich der Schwefel deutlich unterhalb der Ebene, die durch die vier äquatorialen Fluoratome gebildet wird. Vom reinen Cs+SF5− konnten bisher nur Zwillingskristalle erhalten werden. Durch Zufall gelang die Isolierung eines Doppelsalzes (Cs+)6(SF5−)4 (HF2−)2. Die Kristallstrukturanalyse (P4b2, a = 1031,7(15), c = 627,6(9) pm, Z = 1), zeigt das Vorhandensein der gleichen SF5‐Struktureinheiten wie im Rb+SF5−.