[en] The doubly excited ^1,3D⁰ resonance states of Ps^- associated with N=3, N=4 and N=5 Ps thresholds have been investigated using highly accurate correlated wave functions with exponents generated by a quasi-random process. Resonance parameters (both resonance positions and widths) are extracted in the framework of the stabilization method and the complex coordinate rotation method. In addition to many Feshbach resonances below the various Ps thresholds, we have identified two ¹D⁰ shape resonances with one each lying above the N=3 and N=4 thresholds, respectively, and two ³D⁰ shape resonances with one each lying above the N=3 and N=5 thresholds, respectively. The 1^D0 shape resonance associated with N=3 Ps threshold and some other Feshbach resonances are reported for the first time in the literature. (authors)

[en] The fine-structure intervals of the lowest two triplet D states of ⁴He have been obtained by a new method: Ground-state atoms are excited by a discharge to the triplet metastable state, which then undergoes a two-step optical excitation to the triplet D states, where level-crossing measurements are made. The experimental results for ³D₁-³D₃ (MHz) are 1400.67 plus-or-minus 0.29 and 591.25 plus-or-minus 0.14 for the 3 ³D and 4 ³D states, respectively; for ³D₂-³D₃ (MHz) they are 75.97 plus-or-minus 0.23 and 36.15 plus-or-minus 0.24 for 3 ³D and 4 ³D. These values are much more precise than the previously available data, obtained by optical, particle-bombardment level crossing, or beam-foil quantum-beat spectroscopy, and are consistent with the previous data except for one case, where a previous measurement of 3 ³D₂-3 ³D₃ by electron bombardment level-crossing spectroscopy is believed to be in error. These new experimental values for the fine structures of the triplet D state of ⁴He clearly indicate the inadequateness of existing theoretical calculations of these fine structures

[en] Theoretical estimates of the radiative and annihilative decays of the 1¹D₂ charmonium level are discussed within the framework of the nonrelativistic potential model of charmonium. It is argued that the state CHI(3.45) possibly seen in PSI' radiative decay cannot be identified with the 1¹D₂ charmonium level

[en] Highlights: • Two 3d orbitals of iron are critical for activating methane, explaining why high spin atomic iron is inactive. • Emptying the 4s orbital of iron increases activity. • The coordination of Iron can effect its ability to activate methane. Theoretical studies on the activation of the C-H bond in methane by an Iron atom bound to four different sites on a silica model support indicate that the lowest activation barrier is found for the case when the Fe is bound to three exposed silicon sites. A molecular orbital analysis reveals that the transition state is stabilized by two filled 3d orbitals that mix with the HOMO and LUMO of methane respectively, indicating how the energy and occupation of the 3d orbitals determine the reaction barrier. The studies offer a strategy for identifying candidates with optimal electronic structure for maximizing C-H bond activation using non-precious metals.

[en] From a study of experimental phase shifts for p+⁴He elastic scattering at proton energies below 50 MeV we conclude that small D-state admixtures to the dominant S-state configuration exist in the ⁴He ground state. This result is obtained by evaluating a forward dispersion relation for the p+⁴He spin-flip scattering amplitude

[en] Doubly excited or Feshbach-type resonances in helium-like systems have been calculated using the complex-rotation method. Using Hylleraas-type wavefunctions up to 680 terms, we predict resonance parameters (both resonance positions and widths) below the N = 3, 4 thresholds of the hydrogenic systems with the nuclear charge from Z = 2-10. The present results for the lowest ^1.3D^o states in helium below the N = 3 threshold agree well with those of Lindroth. Comparisons are also made with the other calculations for Z > 2 in the literature. (Author)

[en] The D₁ resonance line of francium, which corresponds to the transition 7s²Ssub(1/2)-7p²Psub(1/2), has been observed in a laser spectroscopy experiment performed on line with the mass separator ISOLDE at C.E.R.N. on the isotope of mass 212. A preliminary measurement of the wavelength has been carried out: lambdasub(D1)(²¹²Fr) = (816.90+-0.02) mm, and the fine structure splitting of the excited level has been deduced using a previous measurement of the lambdasub(D2):Δσsub(FS)(7p²Psub(3/2)-7p²Psub(1/2) = (1.686.8+-0.5) cm^-1

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No abstract available

[en] Lifetime observations have been made on 49 energy levels of helium. Good overall agreement with theory is obtained, with significant exceptions, the most striking of which are the 3¹D and 3³D states, where 50% discrepancies with theory and some of the older measurements are found. The new measurements are, however, in harmony with recent results using the Hanle effect. The existance of the upper-state process is clearly delineated by the results of n>6. (author)