Silicon-29 NMR studies of aqueous silicate solutions: Part II. Isotopic enrichment

Silicon-29 NMR spectra have been recorded for aqueous solutions of sodium silicate in the alkaline pH range using silica enriched in the ²⁹Si isotope. Work at low concentration shows that essentially only monomeric orthosilicate ions are present at ca. 0.01 M in silica. At higher concentrations, peaks which lack fine structure indicate species whose silicon nuclei are all equivalent. The experiments have assisted in the difficult process of assigning the spectra of silicate solutions.     

Scattering from impurities in copper,silver and gold-based alloys

Existing data for de Haas-van Alphen lifetime in copper-silver-and gold-based alloys is analyzed. Fitting parameters are given for the partial lifetimes using normalizations compatible with recent theoretical work, and the appropriate conversion factors are also tabulated.     

Measurements of atmospheric water vapour using the absorption band at 7250 cm-1

Measurements of the integrated absorption of the 7250 cm^-1 (1.38 μm) band of water vapour have been made for a 0.5 km horizontal path through the atmosphere. Using published band intensities the absorption values were converted to precipitable water amounts which were found to be about 10% smaller than values determined by wet and dry hygrometry. This difference is probably caused by inaccuracies in the published line parameter values, particularly those involving high rotational energy.     

μSR study of RNi5 intermetallics where R=La,Gd or Tb

Zero-field μSR studies of some hexagonal intermetallic compounds are described. Our LaNI₅ data provide information on the muon localisation site. This site could be one of the deuterium sites deduced from neutron diffraction. A comparison of the temperature dependence of the exponential damping rate, λ(T), of our samples shows that λ(T) is strongly influenced by crystal field effects. The TbNi₅ spectra exhibit two components forT<60 K. We discuss the possible explanations of this result. We see a μSR signal below the magnetic phase transition in GdNi₅. This makes the study of the spin-lattice relaxation rate possible in the ordered magnetic state.     

Infrared spectra and intermolecular potentials of matrix isolated methyl nitrate and methyl-d3-nitrate

The infrared spectra of protonated and deuterated methyl nitrate isolated in a nitrogen matrix have been recorded from 4000 to 250 cm⁻¹. Peaks have been assigned to monomers, pairs, and higher-ordered species by varying the concentration of methyl nitrate in the matrix and also by inducing diffusion of molecules in the matrix. Monomer frequencies were used to calculate the normal coordinates, force constants, and cartesian displacements. Configurations of a pair of methyl nitrate molecules were calculated using an approximate nonbonded atom-atom potential including both Lennard-Jones and electrostatic potentials. The position of minimum energy was established as a function of the distance between molecules as well as angular rotation of the two molecules with respect to one another. Calculations of exciton splittings and shifts for the pair configuration computed to be most stable were evaluated by two site exciton theory and compared to the assigned pair frequencies.     

Energy transfer by intranuclear cascade of pi-zeros produced in antiproton annihilation at rest in nuclear targets

The energy transfer by pi-zeros in the intranuclear cascade initiated by antiproton annihilation at rest in carbon and uranium has been measured to be 28 ± 43 and 232 ± 33 MeV respectively. We estimate the total energy transfer due to all pions to be 75 ± 53 and 447 ± 42 MeV respectively. The uranium value is ～ 17% larger than a recent theoretical prediction. No predictions for carbon are available. Given the expected increase in efficiency of energy transfer from antiproton beams at ～ 3 GeV/c momentum, the prospects for initiating multifragmentation and disintegration of heavy nuclei at these energies appear good.