ABSTRACT
We present a new nucleosynthesis process that may take place on neutron-rich ejecta experiencing an intensive neutrino flux. The nucleosynthesis proceeds similarly to the standard r process, a sequence of neutron captures and beta decays with, however, charged-current neutrino absorption reactions on nuclei operating much faster than beta decays. Once neutron-capture reactions freeze out the produced r process, neutron-rich nuclei undergo a fast conversion of neutrons into protons and are pushed even beyond the ß stability line, producing the neutron-deficient p nuclei. This scenario, which we denote as the νr process, provides an alternative channel for the production of p nuclei and the short-lived nucleus ^{92}Nb. We discuss the necessary conditions posed on the astrophysical site for the νr process to be realized in nature. While these conditions are not fulfilled by current neutrino-hydrodynamic models of r-process sites, future models, including more complex physics and a larger variety of outflow conditions, may achieve the necessary conditions in some regions of the ejecta.
ABSTRACT
The mergers of neutron stars expel a heavy-element enriched fireball that can be observed as a kilonova1-4. The kilonova's geometry is a key diagnostic of the merger and is dictated by the properties of ultra-dense matter and the energetics of the collapse to a black hole. Current hydrodynamical merger models typically show aspherical ejecta5-7. Previously, Sr+ was identified in the spectrum8 of the only well-studied kilonova9-11 AT2017gfo12, associated with the gravitational wave event GW170817. Here we combine the strong Sr+ P Cygni absorption-emission spectral feature and the blackbody nature of kilonova spectrum to determine that the kilonova is highly spherical at early epochs. Line shape analysis combined with the known inclination angle of the source13 also show the same sphericity independently. We conclude that energy injection by radioactive decay is insufficient to make the ejecta spherical. A magnetar wind or jet from the black-hole disk could inject enough energy to induce a more spherical distribution in the overall ejecta; however, an additional process seems necessary to make the element distribution uniform.
ABSTRACT
The heteroleptic lithium amide, [(Me3Sn)(Me3Ge)NLi.(Et2O)]2 (2), reacts with MCl(2) (M = Sn, Ge, Pb) to yield the corresponding cubane complexes [M(mu3-NGeMe3)]4 [M = Sn (3), Ge (4), Pb (5)]. In an analogous reaction with SnCl2, the lithium stannylamide, [(Me3Sn)2NLi.(Et2O)]2 (1), produces the mixed-valent Sn congener [Sn(mu3-NSnMe3)]4 (6). All imidocubanes contain both di- and tetravalent group 14 metals that are bridged by N. These structures are comprised of M4N4 (M = Sn, Pb, Ge) cores that possess varying distortion from perfect cube geometry. The Pb derivative (5) exhibits enhanced volatility and vapor-phase integrity.
ABSTRACT
NH-Bridged tetradentate ligands were synthesized to achieve stable trans Ru(II) bis(polypyridyl) complexes. The polypyridyl part of the ligand was either symmetric, as in N,N-bis(1,10-phenanthroline-2-yl)amine (phen-NH-phen), or asymmetric, as in N-(1,10-phenanthroline-2-yl)-N-(6-yl-dipyridyl[2,3-a:2',3'-c]phenazine)amine (dppz-NH-phen). Protonation of phen-NH-phen with trifluoroacetic acid and the subsequent reaction with RuCl3 yield trans-[Ru(phen-NH-phen)Cl2]. The chloro ligands in this compound can easily be replaced by stronger ligands, such as CH3CN and DMSO. In this way, complexes trans-[Ru(phen-NH-phen)(CH3CN)(DMSO)](PF6)2 (1), trans-[Ru(phen-NH-phen)(DMSO)2](PF6)2 (2), and trans-[Ru(phen-NH-phen)(CH3CN)2](PF6)2 (3) were obtained. X-ray structures were determined for 1 and 3. Following a procedure similar to that used with phen-NH-phen, the complex trans-[Ru(dppz-NH-phen)(CH3CN)2](PF6)2 (4) was obtained. To our knowledge, this is the first reported trans ruthenium(II) bis(polypyridyl) complex with two different polypyridyl ligands in the equatorial plane.
