Inelastic electron scattering from He

The spectra of electrons scattered inelastically from ⁴He have been measured at incident energies from 150 MeV to 400 MeV for scattering angles from 38° to 90°. Through the use of a liquid ⁴He target, a high momentum resolution (≈0.25%) was obtained, and the 20 MeV 0⁺ state of the -particle was observed for the first time in electron scattering. The excitation energy and the total width of this state were determined and are in good agreement with the results from other experimental methods. It was found that the total disintegration cross section appears be smaller than 2(σ_p+σ_n) by more than an order of magnitude at the lowest q²(≈ 0.33 fm⁻²). In earlier work the assumption of a total cross section of 2(σ_p+σ_n) was found to be quite accurate for higher q². As a new result, the partial radiative width for the 0⁺ state is determined to be Γ_rad = 1.1±0.3 meV.     

(e, 2e) spectroscopy of N2—valence momentum distributions and configuration interaction

The noncoplanar symmetric (e, 2e) reaction has been applied to N₂ at 1200, 600 and 400 eV. Separation energy spectra are obtained in the valence region, the observed structure extending to above 60 eV. Electron momentum profiles are measured at a number of separation energies. They agree very well with the momentum distributions for valence orbitals given by SCF calculations. Considerable configuration interaction structure is observed, being primarily due to configuration interaction in the 2σ_g hole state. At 1200 eV the spectroscopic sum rule is satisfied within experimental error, confirming the validity of the analysis.     

Experimental and theoretical binding energy spectra and momentum distributions for the valence orbitals of H2O

The binding energy spectra (10–46 eV) and momentum distributions of the valence orbitals of H₂O have been measured using a new high-sensitivity binary (e,2e) electron spectrometer employing position-sensitive detectors. The binding energy spectrum shows a previously unreported feature at = 27 eV which is shown to be associated with the (2a₁)^?1 ionization process. The region between 25 and 46 eV is compared with previous (e,2e) and X-ray photoelectron measurements as well as with several existing and new many-body calculations indicating a splitting of the 2a₁ ionization pole strength. In addition the separate momentum distributions of the three outer valence orbitals of H₂O have been obtained from deconvoluted binding energy spectra run at a series of azimuthal angles. The results, which show considerably improved signal-to-noise ratio over earlier measurements using single-channel instrumentation are compared with spherically averaged momentum distributions calculated with a variety of wavefunctions.     

Explicit non-'t Hooft rational solutions of the Atiyah-Drinfeld-Hitchin-Manin instanton matrix equations for SU(2r)

The Atiyah-Drinfeld-Hitchin-Manin instanton matrix equations may be written as a pair, one quadratic and one linear. The explicit general solution of the quadratic equation is given in terms of rational functions of free parameters, thus reducing the ADHM equations to a single equation. For SU(2r), large families of explicit solutions, rational in free parameters, are constructed by this method. These new families are generally about twice as large as the previously known 't Hooft families, and contain non-'t Hooft solutions for every r ? 1.     

Matchings in graphs II

Proofs are given of theorems of Lovász and Brualdi on the existence in a finite simple graph of matchings required to meet vertices in a given set A of vertices. An alternating chain condition is obtained for a maximum matching to meet all the vertices in A.     

Crystal structure and single-crystal polarized spectrum of 1,4,7,10-tetraazadecanebis(N-methylimidazole)-nickel(II) perchlorate

The Ni(II) complex of 1,4,7,10-tetraazadecane (trien) andN-methylimidazole (Meim), [Ni(trien)(Meim)2](ClO₄)₂, crystallizes in the triclinic system witha=7.934(1),b=9.770(2),c=16.108(2) Å,=98.54(1),gb=97.16(1), and =98.10(1)°, The structure was refined by least-squares techniques to anR factor of 0.049 for 3729 observed reflections. The complexed nickel ion is octahedral. The trien ligand is bonded through its four nitrogens in the usual fashion, so that the terminal nitrogen atoms occupy;trans-positions on the octahedron. The remaining two coordination sites are filled by the Meim ligands. The Ni-N bond distances are normal, and range from 2.103(3) to 2.156(3) Å. The polarized single-crystal spectra are interpreted on the basis of an octahedral ligand field having a tetragonal distortion along the H₂N-Ni-NH₂ axis.     

NMR studies in the heterocyclic series. XX—a carbon-13 NMR study of the structures of N-hydroxybenzotriazole and its acylated derivatives

Assignment of the carbon resonances in nine derivatives of N-hydroxybenzotriazole has been carried out. The ¹³C NMR method enables tautomeric N-hydroxy and N-oxide and isomeric O- and N-acyl structures to be identified. In DMSO, the predominant tautomer of N-hydroxybenzotriazole was found to be the N-hydroxy form. The structure of the benzoate and methyl and phenyl carbonate esters were likewise established, but for the two latter compounds, hydrolysis of the equilibrating O- and N-acyl isomers imposed some limitations on the usefulness of the technique.