Delayed onset of intermolecular bonding in the water adlayer on Ru(001) due to the presence of preadsorbed oxygen

Infrared reflection absorption spectroscopy has been employed to study adsorption of water on Ru(001) at liquid nitrogen temperatures. For even the lowest H₂O coverages a broad absorption band at ≈3400 cm^?1 is observed on the clean surface, indicating formation of hydrogen-bonded clusters Small amounts of preadsorbed oxygen delay the clustering process.     

Reactions of transition-metal carbonyls with anhydrous HF

The reactions of a wide range of transition-metal carbonyls with anhydrous HF are described. In particular, Ru₃(CO)₁₂, Os₃(CO)₁₂ and Ir₄(CO)₁₂ give the solution stable [Ru₃(CO)₁₂H]⁺, [Ru(CO)₅H]⁺, [Os₃(CO)₁₂H]⁺, [Os(CO)₅H]⁺ and [Ir₄(CO)₁₂H₂]²⁺ respectively, which have been characterised by a combination of ¹H and ¹³C NMR spectroscopy.     

High fidelity sorting of remarkably similar components via metal-mediated assembly

Subtle differences in ligand coordination angle and rigidity lead to high fidelity sorting between individual components displaying identical coordination motifs upon metal-mediated self-assembly. Narcissistic self-sorting can be achieved between highly similar ligands that vary minimally in rigidity and internal coordination angle upon combination with Fe(ii) ions and 2-formylpyridine. Selective, sequential cage formation can be precisely controlled in a single flask from a mix of three different core ligands (and 33 total components) differing only in the hybridization of one group that is uninvolved in the metal coordination process.     

Synthesis and characterization of colloidal ternary ZnCdSe semiconductor nanorods

For the synthesis of colloidal ternary ZnCdSe nanorods, CdSe nanorods were first prepared under a mixture of tetradecylphosphonic acid/trioctylphosphine oxide surfactants at 250 degrees C, and then ZnSe shell layer was grown onto CdSe nanorods at 180 degrees C, forming CdSeZnSe core/shell nanorods. Green-yellow emitting ternary ZnCdSe nanorods were obtained by a subsequent alloying process at 270 degrees C for 1-3 h through the diffusion of Zn ions into CdSe nanorods. The photoluminescence quantum yield (QY) of ZnCdSe nanorods was 5%-10%, which is higher than that from pristine CdSe nanorods (0.6%). The QY of these alloy nanorods depends on the alloying time and is discussed in terms of compositional disorders and defects produced by the alloying process. The Raman and time resolved photoluminescence spectroscopies were used to understand the detailed alloying process from CdSeZnSe core/shell to ZnCdSe alloy nanorods.     

Blocks with nonabelian defect groups which have cyclic subgroups of index p

In representation theory of finite groups, one of the most important and interesting problems is that, for a p-block A of a finite group G where p is a prime, the numbers k(A) and ℓ(A) of irreducible ordinary and Brauer characters, respectively, of G in A are p-locally determined. We calculate k(A) and ℓ(A) for the cases where A is a full defect p-block of G, namely, a defect group P of A is a Sylow p-subgroup of G and P is a nonabelian metacyclic p-group M _n+1(p) of order p ⁿ⁺¹ and exponent p ⁿ for n \geqslant 2{n \geqslant 2}, and where A is not necessarily a full defect p-block but its defect group P = M _n+1(p) is normal in G. The proof is independent of the classification of finite simple groups.     

ATMOSPHERIC SUN PROTECTION FACTOR ON CLEAR DAYS: ITS OBSERVED DEPENDENCE ON SOLAR ZENITH ANGLE AND ITS RELEVANCE TO THE SHADOW RULE FOR SUN PROTECTION

Global irradiances measured in seven 5-nm bands of UV-B at Rockville, MD (39.1 degrees N, 77.1 degrees W) on 28 clear days near the summer solstice are convoluted with the erythemal action spectrum of human skin to determine dose rates at various hours of the day. These rates are averaged with respect to solar zenith angle to obtain the diurnal variation of mean dose rate and of the Sun Protection Factor (SPF) of the atmosphere (reciprocal of the normalized atmospheric transmissivity) on a typical clear summer day in Rockville. At a 45 degrees zenith angle the atmospheric SPF is computed to be 2.7 and increases rapidly to greater than 7 at 60 degrees. Dose rates are integrated with respect to time to obtain estimates of mean doses for various periods during clear days at Rockville in mid summer and near the autumnal equinox. In mid summer the effective erythemal UV-B exposure during the period when the solar zenith angle is less than 45 degrees is about five times greater than that during the remainder of the day. These observations provide scientific basis for a shadow rule for solar UV-B protection: when shadows are shorter than objects casting them, sunburn is much more likely than at other times.     

Formal total synthesis of salicylihalamides A and B

An efficient synthesis of the macrolactone 3 of the salicylihalamides in 10 linear steps from alkene 6 is described. The key steps involved a Stille coupling between the chiral stannane 5 and benzyl bromide 4, which produced alkene 15 in good yield, and subsequent base-induced macrolactonization then gave compound 3. Macrolactone 3 was then converted into the known salicylihalamide A intermediate 18 in a three-step sequence. Compound 3 was also converted into another known salicylihalamide A and B intermediate 23 in a five-step sequence.     

The surface temperature dependence of the inelastic scattering and dissociation of hydrogen molecules from metal surfaces

High-dimensional, wave packet calculations have been carried out to model the surface temperature dependence of rovibrationally inelastic scattering and dissociation of hydrogen molecules from the Cu(111) surface. Both the molecule and the vibrating surface are treated fully quantum-mechanically. It is found, in agreement with experimental data, that the surface temperature dependence of a variety of dynamical processes has an Arrhenius form with an activation energy dependent on molecular translational energy and on the initial and final molecular states. The activation energy increases linearly with decreasing translational energy below the threshold energy. Above threshold the behavior is more complex. A quasianalytical model is proposed that faithfully reproduces the Arrhenius law and the translational energy dependence of the activation energy. In this model, it is essential to include quantized energy transfer between the surface and the molecule. It further predicts that for any process characterized by a large energy barrier and multiphonon excitation, the linear change in activation energy up to threshold has slope-1. This explains successfully the universal nature of the unit slope found experimentally for H2 and D2 dissociation on Cu.