Vibrational spectra of polycrystallineMNCO (M = K,Rb, Cs)

IR and Raman spectra are reported for polycrystalline samples of the isomorphousMNCO (M=K,Rb,Cs). The lattice modes are generally assignable to the symmetry species of the factor groupD _4h by analogy with those ofMN₃, but the internal modes are not, in general, interpretable by any known practical analysis. These spectral features may be associated with the disorder of the NCO^– ions in the crystal structure.     

Gas electron diffraction study of the vapour over dimethylamine-gallane leading to an improved structure for dimeric dimethylamidogallane, [Me2NGaH2]2: a cautionary tale

Dimethylamine-gallane is relatively slow to decompose in a closed system and vaporises at low temperature primarily as Me2(H)N.GaH3 molecules which can be trapped in a solid Ar matrix and characterised by their IR spectrum. Under the conditions needed to secure a useful gas electron diffraction (GED) pattern, however, the vapour was found to consist of dimeric dimethylamidogallane molecules, [Me2NGaH2]2, formed from the secondary amine adduct by elimination of H2, and the most reliable structure for which has been determined. Salient structural parameters (r(hl) structure) were found to be: r(Ga-N) 202.6(2), r(Ga-H) 155.6(8), r(N-C) 148.0(3), r(C-H) 111.2(6) pm; Ga-N-Ga 90.7(1), C-N-C 109.3(5), N-C-H 109.9(10) and H-Ga-H 119.4(42) degrees.     

The vibrational spectra of the cyanide ligand revisited: terminal cyanides

A comparison is made between the vibrational characteristics of the carbonyl and cyanide ligands. There are significant differences; the latter has a smaller dipole moment and a larger quadrupole moment associated with the bond stretch. This quadrupole moment may be linked to the observation that the totally symmetric nu(CN) mode does not lie at the highest frequency for some cyanide complexes. There are problems with the pi-bonding model commonly used to interpret the nu(CN) data. For instance, for the first transition row hexacyanoanions, the spectra are almost independent of t2g occupancy but are very sensitive to the formal charge. It is suggested that the observed nu(CN) frequency shifts on complex formation are in large measure determined by the effective charge on the cation to which the cyanide group is attached, and a new model, the Internal Vibrational Stark Effect, is suggested to account for this. The model is supported by DFT calculations. Raman spectra of some cubic cyano species are reported, along with polarization and intensity data.     

Synthesis of a 5-alkoxypyrido[3,4-d]pyrimidin-4(3H)-one derivative via directed ortho-metallation of a pyridine analogue

The synthetic strategy towards a 5-alkoxypyrido[3,4-d]pyrimidin-4(3H)-one is described, utilizing palladium catalyzed amination of a bromopyridine, and subsequent directed ortho-metallation/carboxylation as the key steps.     

New limit on the lepton-flavor-violating decay μ+→e+γ

We present a new result based on an analysis of the data collected by the MEG detector at the Paul Scherrer Institut in 2009 and 2010, in search of the lepton-flavor-violating decay μ(+)e(+)γ. The likelihood analysis of the combined data sample, which corresponds to a total of 1.8×10(14) muon decays, gives a 90% C.L. upper limit of 2.4×10(-12) on the branching ratio of the μ(+)→e(+)γ decay, constituting the most stringent limit on the existence of this decay to date.     

Fabrication of Step-and-Flash Imprint Lithography (S-FIL) templates using XeF<Subscript>2</Subscript> enhanced focused ion-beam etching

The fabrication of Step-and-Flash Imprint Lithography (S-FIL) templates with line widths of 50 nm is described in this work. The structures have been patterned using a Ga⁺ focused ion beam (FIB) in a quartz template. FIB milling is generally accompanied with re-deposition effects, which represent a hindrance to densely patterned nanostructures required in most NIL applications. To reduce these re-deposition effects, in this research, xenon difluoride (XeF₂) enhanced FIB etching was applied that also increases the material removal rates in comparison to pure kinetic ion sputtering. To optimise the process when using XeF₂ gas the following ion scanning parameters have been examined: ion dose, beam current, dwell time and beam overlap (step size). It has been found that the assisting gases at very low doses do not bring significant etching enhancements whilst the sputtering rates have increased at high doses. Using the XeF₂ gas-assisted etching, FIB structuring has been used to fabricate <100 nm structures onto quartz S-FIL templates. The presence of XeF₂ considerably enhances the etching rate of quartz without any significant negative effects on the spatial resolution of the FIB lithographic process and reduces the template processing time.     

Angular distribution of the reaction np → dπ0

Differential cross sections of the reaction np → dπ⁰ have been measured for incident neutron energies between 470 MeV and 590 MeV. The angular distributions are fitted by a power series. A significant cos⁴θ contribution is found.     

Kinetic energy of π− p-atoms in liquid and gaseous hydrogen

We have measured the Doppler broadening of neutron time-of-flight spectra from the reaction π⁻ p → π⁰ + n in atomic states. From the data, we infer that the kinetic energy distribution of π⁻ p-atoms in liquid and gaseous hydrogen contains discrete ‘high-energy’ components with energies as high as 200 eV attributed to Coulomb de-excitation. In liquid hydrogen, evidence for Coulomb de-excitation transitions with Δn = 2 has been found. This revised version was published online in August 2006 with corrections to the Cover Date.