Unraveling the electronic structure of transition metal dimers using resonant four‐wave mixing

The potential of two‐color resonant and degenerate four‐wave mixing spectroscopy for investigations of the complex spectra of transition metal dimers is explored. Two‐color resonant and degenerate four‐wave mixing spectroscopy scans of the well‐known A‐X and B‐X transitions in Cu₂ are reported and compared with previous experimental data obtained from standard single‐resonance techniques. The selectivity of the method is shown to enable the measurement of isotopologue pure spectra without the need for isotopically enriched metal targets. Specific subsets of the rovibronic structure are separated in a congested spectral region of overlapping transitions. The sensitivity of the method compares satisfactorily with linear spectroscopic methods such as laser‐induced fluorescence and cavity ring‐down. A new laser vaporization source for the production of transition metal dimers and clusters has been constructed. The new design aims for a high number density and maximum possible shot‐to‐shot stability. The possibilities of further applications of non‐linear four‐wave mixing spectroscopy to Cu₂ and other transition metal dimers are discussed. Copyright © 2015 John Wiley & Sons, Ltd.     

Optimal signaling with cheap talk and money burning

We study Sender-optimal signaling equilibria with cheap talk and money-burning. Under general assumptions, the Sender never uses money-burning to reveal all states, but always wants to garble information for at least some states. With quadratic preferences and any log-concave density of the states, optimal communication is garbled for all states: money-burning, if used at all, is used to adjust pooling intervals. This is illustrated by studying in depth the well-known uniform-quadratic case. We also show how the presence of a cost of being “caught unprepared” that gives rise to a small change in a common assumption on the Receiver’s utility function makes full revelation through money-burning Sender-optimal.     

Oxidative properties of a nonheme Ni(II)(O2) complex: Reactivity patterns for C-H activation, aromatic hydroxylation and heteroatom oxidation

Density functional theory calculations on the reactivity of a Ni(II)-superoxo complex in C-H bond activation, aromatic hydroxylation and heteroatom oxidation reactions have been explored; the Ni(II)-superoxo complex is able to react with substrates with weak C-H bonds and PPh(3).     

Time-resolved tryptophan fluorescence in flavodoxins

The time-resolved fluorescence characteristics of tryptophan in flavodoxins isolated from the bacteriaDesulfovibrio gigas, Desulfovibrio vulgaris, Clostridium beijerinckii, andMegasphaera elsdenii were examined. The fluorescence decays were recorded using pulsed synchrotron radiation as the excitation source and time-correlated single-photon counting in detection. The results were analyzed as lifetime distributions using the maximum entropy method. Comparison of the fluorescence decays of normal and flavin mononucleotide-depleted flavodoxins demonstrates that radiationless energy transfer from tryptophan to flavin occurs in all flavodoxins investigated. On comparing the lifetime distribution patterns of apo and holoflavodoxins, it was noticed that a certain amount of apoprotein is present in all holoflavodoxin samples. The three-dimensional structure of two flavodoxins allowed us to compare experimental with theoretical transfer rates and the results were in fair agreement.     

Liquid-crystalline phthalocyanines revisited

A Commentary on the paper “Homologous series of liquid-crystalline metal free and copper octa-n-alkoxyphthalocyanines„, by J. F. van der Pol, E. Neeleman, J. W. Zwikker, R. J. M. Nolte, W. Drenth, J. Aerts, R. Visser and S. J. Picken. First published in Liquid Crystals, 6, 577-592 (1989).     

Applications of TOF neutron diffraction in archaeometry

Neutron radiation meets the demand for a versatile diagnostic probe for collecting information from the interior of large, undisturbed museum objects or archaeological findings. Neutrons penetrate through coatings and corrosion layers deep into centimetre-thick materials, a property that makes them ideal for non-destructive examination of objects for which sampling is impractical or unacceptable. A particular attraction of neutron techniques for archaeologists and conservation scientists is the prospect of locating hidden materials and structures inside objects. Time-of-flight (TOF) neutron diffraction allows for the examination of mineral and metal phase contents, crystal structures, grain orientations, and microstructures as well as micro- and macro strains. A promising application is texture analysis which may provide clues to the deformation history of the material, and hence to specific working processes. Here we report on instructive examples of TOF neutron diffraction, including phase analyses of medieval Dutch tin-lead spoons, texture analyses of bronze specimens as well as of 16th-century silver coins. PACS 61.12.-q; 81.05.Bx; 81.70.Jd     

Photochemical and thermal (2+2)-cycloaddition of thioxanthenethione to some aliphatic pentatetraenes

Reaction of thioxanthene-9-thione 1 with the alkyl substituted pentatetraenes 2a-g gives mixtures of the thietanes 3a-g and 4a-g. The ratio $\text{3}\text{4}$ in the thermal reaction is strongly dependent on the substituents. In the case of 2a thermal rearrangement of the product leads to a stable thiete.     

Resistivity of single-crystalline UPt3 and its pressure dependence; Interpretation by a spin-fluctuation model

Resistivity measurements on a series of uranium-platinum compounds were carried out in the range 1.3 up to 300 K and pressures up to 5 kbar. The resistivity of single-crystalline UPt₃ is strongly anisotropic and points to pronounced spin-fluctuation effects that are partly suppressed at a pressure of 4 kbar. In paramagnetic UPt₂ and UPt₅ spin-fluctuation effects are less pronounced, whereas in ferromagnetic UPt the spin-disorder scatter is dominant above 27 K.     

PHOTOTAUTOMERISM OF LUMICHROME IN METHANOL-ACETIC ACID MIXTURES. A STEADY-STATE AND TIME-RESOLVED FLUORESCENCE STUDY

Abstract— Fluorescence lifetimes of 3-methyllumichrome dual fluorescence at 440 nm (alloxazinic) and 520 nm (isoalloxazinic) and of 1,3-dimethyllumichrome, which is unable to phototautomerize, at the same wavelengths have been measured in methanol-acetic acid mixtures. The fluorescence decays of both lumichromes studied are exponential and the phototautomeric fluorescence of 3-methyllumichrome is created within approximately 50 ps. From the initial values of about 0.9 ns (alloxazinic) and 6.4 ns (isoalloxazinic) in 5% acetic acid the lifetimes shorten considerably with increasing acid concentration reaching 0.2 ns for 1,3-dimethyllumichrome and 80 ps for the alloxazinic and 2.4 ns for the isoalloxazinic form of 3-methyllumichrome in pure acid. Static and dynamic fluorescence quenching constants were estimated. The differences in the quenching rate and equilibrium constants of both lumichromes are interpreted in terms of different equilibria of hydrogen bond formation in ground and excited state as influenced by steric effects of the methyl substituent at the N-l position in 1,3-dimethyl. The hydrogen bonding atN–10 of 3-methyllumichrome with acetic acid is a prerequisite for additional hydrogen bonding at N-l enabling excited state proton transfer.