An amplitude analysis of ππ scattering from new data on the reaction π−p→π+π−n

We have carried out a partial-wave analysis of ππ scattering in the mass range 1.0 to 2.08 GeV/c². We find solutions similar to those obtained in previous analyses below 1.8 GeV/c² but, in addition, we obtain a new solution which does not suffer from violations of unitarity and is compatible with data from other channels. This solution, when continued to 2.08 GeV/c², shows a g meson with mass and width of 1.734± 0.010 GeV/c²and 0.322±0.035 GeV/c² respectively, and an h meson with mass 1.935±0.013 GeV/c²and width 0.263±0.057 GeV/c². The L = 2 partial wave contains the f meson and an additional resonance with parameters m = 1.502±0.025 Gev/c², Γ = 0.165±0.042 GeV/c²and x = 0.19±0.03. If we associate this state with the f′(1514), our ππ branching fraction is considerably higher than previous determinations. An SU(3) fit to the 2⁺ nonet yields a mixing angle of 38.4± 1.3°.     

Structure of Rb-III: novel modulated stacking structures in alkali metals

The crystal structure of Rb-III, stable between 13 and 17 GPa, has been determined from quasi-single-crystal x-ray diffraction data. It is orthorhombic, space group C222(1), with 52 atoms in the unit cell, and has an 8-10-8-8-10-8 stacking of 8- and 10-atom layers. The recently reported 84-atom structure of Cs-III can be understood as an 8-8-10-8-8-8-8-10-8-8 stacking of the same layers. These represent a new class of modulated elemental structures.     

Quantitative phase radiography with polychromatic neutrons

We develop and experimentally demonstrate a formalism that allows accurate phase imaging using neutron sources producing highly polychromatic beams. The results of measurements from a rectangular block of silicon compare favorably with theoretical simulations based upon the known composition and geometry of the block. The increased flux and reduced exposure times will permit a simple extension of the technique to tomographic phase imaging.     

Wideline NMR studies of oriented nylon 66 under tensile stress

NMR linewidth studies of nylon 66 as a function of temperature and applied tensile stress have been conducted. The principal motional transition temperature was found to be shifted to higher temperatures with stress application by 9°C./g./den. At any given temperature, increased stress resulted in an increased linewidth. An attempt was made to correlate the shift in the motional transition temperature with the concept that a segment experiencing motion must do work against the applied tensile stress.     

Production of muon pairs in the continuum region by 39.5 GeV/cπ±, K±, p and p beams incident on a copper target

General features of the inclusive hadroproduction of muon pairs of mass greater than 1.5 GeV/c² are shown. For incident π^?, the data extend up to M=5.7 GeV/c² (i.e.M²/s≈0.4). The scaling cross section M³dσ/dM for π^?N reactions is much flatter than that for pN reactions and exceeds the latter by two to three orders of magnitude at large M²/s.     

Ba-IV-type incommensurate crystal structure in group-V metals

The long-unknown crystal structure of Bi-III has been solved. It comprises a body-centered-tetragonal (bct) "host" and a bct "guest" component made up of chains that lie in channels in the host; the guest is incommensurate with the host along the tetragonal c axis. Diffraction data for Sb-II reveal that it too can be fitted with the same composite structure. The structures of these two high-pressure phases of Bi and Sb are similar to those reported recently in the alkaline-earth metals Ba and Sr.     

Triplet 1,3-diphenylpropynylidene (Ph-C-C-C-Ph)

Photolysis (lambda>571 nm) of 1,3-diphenyldiazopropyne (9) affords triplet 1,3-diphenylpropynylidene (3), as characterized by IR, UV/vis, and EPR spectroscopy in low-temperature matrices. Two conformational isomers of triplet 3 are spectroscopically distinguishable. The initially formed, non-relaxed conformer is believed to reflect the geometry of the diazo precursor, as enforced by the rigid matrix. Annealing the matrix permits the structure to relax to the equilibrium D2d geometry. The highly symmetric equilibrium structure of 3 is best envisioned as a 1,3-allenic diradical. Density functional theory calculations suggest that the equilibrium structure does not exhibit a bond-localized structure that would be characteristic of an acetylenic carbene. Chemical trapping with O2, however, affords products that are familiar as carbene trapping products: carbonyl oxide 10, ketone 11, and dioxirane 12. Irradiation (lambda>261 nm) of triplet 1,3-diphenylpropynylidene (3) results in cyclization to singlet diphenylcyclopropenylidene (6), a process that is photochemically reversible at lambda=232 nm. Diphenyl-1,2-propadienylidene (7) was not observed under any irradiation conditions.     

Photochemical charge transfer excitation of trans-4-stilbazole at a silver electrode

When adsorbed at the surface of a polycrystalline silver electrode, trans-4-stilbazole photoreacts, in the presence of dissolved oxygen, to form trans-4′-hydroxy-4-stilbazole. The structure of the photoproduct is confirmed by (1) a comparison of the surface Raman results with the normal Raman of trans-4′-hydroxy-4-stilbazole, and by (2) by ex-situ analysis of the irradiated electrode surface using high-resolution mass spectrometry. The surface photochemistry appears to be a one-photon process whose threshold wavelength lies in the middle of the visible range though neat trans-4-stilbazole absorbs only in the ultraviolet. The surface Raman intensity of the photoproduct increases synchronously with the Faradaic current of oxygen reduction. Attendant incorporation of oxygen exclusively at the 4′ position of end-on trans-4-stilbazole evidences a photo-initiated electron transfer from the electrode to oxygen reducing at the other end of the molecule. Scattering from stilbazole adsorbed at two different surface sites is evident in the surface Raman spectrum: charged (Ag⁺) sites and more neutral surface sites. We assign excitation profile maxima for stilbazole at Ag⁺ sites and the photochemical initiation to a silver-to-stilbazole charge transfer at those sites. Ab-initio molecular orbital calculations on a model composed of a ground state Li⁰-trans-4-stilbazole and the anion radical excited state Li⁺-trans-4-stilbazole⁻ reveal a low-energy transition that supports assignment of the visible excitation to a silver-to-stilbazole electron transfer.     

Charge compensation for imaging large insulating samples by using secondary ion tandem mass spectrometry

A charge compensation technique has been developed for secondary ion mass spectrometry and imaging of insulating samples as large as 1 cm² using a triple quadrupole-based microprobe. The microprobe secondary ion extraction field is synchronized with a periodic primary Cs⁺ beam to allow a sheetlike beam of 5-eV electrons to pass over the sample surface when the extraction field is zeroed. Electrons are attracted to, and neutralize, any points on the sample that have accumulated positive charge. Positive secondary ion images from Teflon®, a well-known insulator, illustrate the effectiveness of charge compensation. Locating and identifying analytes on dry filter paper by using tandem mass spectrometry are also demonstrated.