Threshold electroproduction experiments and the axial vector form factor

Data from three coincidence experiments which measure the cross section for π⁺ electroproduction around threshold are compared. Application of the PCAC motivated pseudovector Born approximation model yields corresponding values of the nucleon axial vector form factor for spacelike momentum transfer up to 0.6 GeV². Attention is paid to possible theoretical uncertainties and to the influence of the first pion-nucleon resonance. (Recent single arm SLAC results are also included.)     

Calculated beam intensities for low energy positron diffraction

The intensity of the specular beam for low energy positron diffraction (LEPD) from the Cu(111) surface is calculated in the energy range 20–150 eV. Close agreement is found with the first experimental data for LEPD published recently. This result indicates that LEPD may be exploited as a technique for determining surface structures in the near future. It is suggested that LEPD may have advantages in surface structure analysis in comparison with low energy electron diffraction (LEED).     

Kaon electroproduction

The simple Regge absorption model used previously for high-energy charged kaon photoproduction is here directly extended to electroproduction, thus providing a framework for theoretical discussion and interpretation of future experimental efforts.     

Near-threshold electron impact excitation of ultraviolet-emitting levels of helium atoms

The excitation by electron impact of levels of helium atoms that decay by emission of ultraviolet light has been studied as a function of incident energy up to approximately the first ionization energy. The width (FWHM) of the energy spread of the incident beam was less than 30 meV. A crossed-beam interaction region was used and UV photons emitted approximately normally to the electron and gas beam directions were detected by a channel electron multiplier. Precautions were taken to avoid detection of scattered electrons and metastable atoms by the photon detector. The onset position of the lowest excited level was used in calibrating the incident energy scale. The energies of resonance structures in the cross-sections could therefore be obtained and are compared with the results of experiments detecting other products of the interaction.     

Magnetic properties of ferromagnetic VFe alloys near the critical concentration for ferromagnetism

Magnetic measurements on a series of FeV alloys in the composition range 29–35 at .% Fe have been interpreted in terms of a local environment model. Values for the moment and density of magnetic clusters have been determined. Good agreement is obtained between values obtained from Curie constants, and those estimated from the critical coefficients. The results may be understood in terms of a random distribution of solute atoms.     

Conversion of alpha-haloaldehydes into acylating agents by an internal redox reaction catalyzed by nucleophilic carbenes

Reactivity umpolung allows us to consider nontraditional bond disconnections. We report herein that treatment of an alpha-haloaldehyde with a nucleophile in the presence of catalytic amounts of nucleophilic carbenes results in an internal redox reaction giving rise to a dehalogenated acylating agent as an intermediate by a new reaction manifold. A brief illustration of the scope of this reaction is presented along with evidence supporting the direct intervention of the carbene in the acylation step.