Charge-exchange mechanisms at the threshold for inelasticity in Ne+ collisions with surfaces

We present a study on scattering of 100–1400 eV Ne+ ions off Mg, Al, Si, and P surfaces. Exit energy distributions and yields of single-scattered Ne+ and Ne2+ were separately measured to investigate charge exchange mechanisms occurring at the onset of inelastic losses in binary hard collision events. At low incident energies, collisions appear elastic and projectile ion survival is dominated by nonlocal Auger-type neutralization involving the target valence band. However, once a critical Rmin (distance of closest approach) is reached, three phenomena occur simultaneously: Ne2+ generation, reversal of the Ne+ yield trend, and inelastic losses in Ne+ and Ne2+. Rmin values for the Ne2+ turn-on agree very well with the L-shell overlap distances of the colliding partners, suggesting that electron transfer involving the highly promoted 4fsigma molecular orbital (correlated to the Ne 2p) at close internuclear distance (~0.5 Å) is responsible. For the Ne+ yield, a clear transition from nonlocal neutralization to Rmin-dependent collision induced neutralization was observed. Binary collision inelasticities (Qbin) were evaluated for Ne+ and Ne2+ off Al and Si by taking into account electron straggling. Saturation-like behavior at RminNe** (2p43s2, 41–45 eV) and Ne+-->Ne+** (2p33s2/3s3p, 69–72 eV), followed by autoionization as the projectile leaves the surface region to give Ne+ and Ne2+. In contrast, Qbin values for Ne2+ at the +2 turn-on were seen much lower (35–40 eV off Al, 55–60 eV off Si) than that required for double promotion—eliminating the possibility that Ne2+ is only generated in double excitation of surviving Ne+. Thus single-electron excitation appears to be more important in the threshold region compared to the two-electron events seen at higher collision energies. In addition, the Ne+[Single Bond]P system shows striking similarities with the other target cases from the perspective of a well-defined Ne2+ turn-on, continually increasing Ne2+ yield with impact energy, and inelasticity values which point to the same 4fsigma excitation pathway. The decreasing Rmin requirement for higher target Z in terms of Ne2+ production has been confirmed for the Mg through P series, where hard collision excitation is governed by L-shell orbital overlaps

Evidence of Simultaneous Double-Electron Promotion in F+ Collisions with Surfaces

A high-flux beam of mass-filtered F+ at low energy (100–1300 eV) was scattered off Al and Si surfaces to study core-level excitations of F0 and F+. Elastic scattering behavior for F+ was observed at energies 450 (700) eV off Al (Si) produces F2+—behavior which is remarkably similar to Ne+ off the same surfaces. Inelasticities measured for single collision events agree well with the energy deficits required to form (doubly excited) F** and F+** states from F0 and F+, respectively; these excited species most likely decay to inelastic F+ and F2+ via autoionization

Reactions of cyclomanganated complexes with carbon disulfide: routes to η²-aryldithiocarboxylate-Mn(CO)₄ complexes and to the trithiocarbonate complex (μ₃-CS₃)₂Mn₄(CO)₁₆

Reaction of cyclomanganated aryl ketones with CS₂ proceeds with insertion into the Mn–C bond to give η²-dithiocarboxylato–Mn(CO)₄ compounds. With other cyclomanganated substrates such as that from Ph₃P=S and also with Mn₂(CO)₁₀, CS₂ gives (μ₃-CS₃)₂Mn₄(CO)₁₆ with bridging trithiocarbonate ligands

Manganese carbonyl-mediated reactions of azabutadienes with phenylacetylene, methyl acrylate and other unsaturated molecules

Reaction of PhCH₂Mn(CO)₅ with l,4-di-aryl-1-aza-1,3-butadienes gave substituted pyrrolinonyl rings which were η⁴-coordinated to a Mn(CO)₃ group. These are formed by intramolecular CO insertion into a (non-isolated) cyclomanganated intermediate, followed by cyclisation. Other unsaturated reagents (PhC≡CH, CH2=CHCOOMe, PhNCO) gave products arising from insertion of these, including a structurally characterised tri-aryl-η⁵-azacyclohexadienyl-Mn(CO)₃ complex from the reaction with the alkyne. PhCH₂Mn(CO)₅ reacts with l,4-di-aryl-1-aza-1,3-butadienes in the presence of unsaturated substrates to give products based on a cyclomanganated intermediate

A phylogenetic analysis of revolution and afterlife beliefs

Beliefs about the fate of humanity and the soul after death may structure behaviours of religious groups. Here we test theories from religious studies: that belief in an imminent apocalypse co-evolved with and facilitated revolutionary violence, whereas belief in reincarnation caused people to acquiesce to existing social orders and withdraw from political activism. We test these hypotheses by building a cultural phylogeny of historical Islamic sects and schools from the seventh to twentieth centuries and use phylogenetic comparative methods to show that these two types of belief display distinct relationships with intergroup violence. There is substantial evidence that apocalyptic beliefs co-evolved with revolutionary violence, whereas reincarnation beliefs were evolutionarily stable in peaceful groups. In both cases, violence precedes the emergence of beliefs, which suggests that conditions that generate revolutionary violence changed beliefs rather than beliefs generating violence. We also found that apocalyptic beliefs are associated with accelerated group extinction, although causal relationships cannot be determined

Electron-acoustic plasma waves: oblique modulation and envelope solitons

Theoretical and numerical studies are presented of the amplitude modulation of electron-acoustic waves (EAWs) propagating in space plasmas whose constituents are inertial cold electrons, Boltzmann distributed hot electrons and stationary ions. Perturbations oblique to the carrier EAW propagation direction have been considered. The stability analysis, based on a nonlinear Schroedinger equation (NLSE), reveals that the EAW may become unstable; the stability criteria depend on the angle $\theta$ between the modulation and propagation directions. Different types of localized EA excitations are shown to exist.Comment: 10 pages, 5 figures; to appear in Phys. Rev.