Kβ X-ray emission spectroscopy offers unique chemical bonding insights: revisiting the electronic structure of ferrocene

Kβ X-ray emission spectroscopy (XES) is emerging as a powerful tool for the study of chemical bonding. Analyses of the Kβ XES of ferrocene (Fc) and ferrocenium (Fc(+)) are presented as further demonstrations of the capabilities of the technique. Assignments of the valence to core (V2C) region of these spectra as electric dipole-allowed cyclopentadienyl (Cp) → Fe 1s transitions demonstrate that XES affords electronic structural insight into the energetics of ligand-based molecular orbitals (MOs). Combined with K-edge X-ray absorption spectroscopy (XAS), we show that XES can provide analogous information to photoemission spectroscopy (PES). Density functional theory (DFT) analyses reveal that the V2C transitions in Fc/Fc(+) derive their intensity from Fe 4p admixture (on the order of 5-10%) into the Cp-based MOs from which they originate. These 4p admixtures confer bonding character to the Cp-based a(2u) and e(1u) MOs to at least the extent of backbonding contributions to frontier MOs from higher-lying Cp π* MOs.     

Synthesis and Structure of Amido‐ and Imido(pentafluorophenyl)borane Zirconocene and Hafnocene Complexes: N?H and B?H Activation

Treatment of Me₂S ? B(C₆F₅)_nH_3?n (n=1 or 2) with ammonia yields the corresponding adducts. H₃N ? B(C₆F₅)H₂ dimerises in the solid state through N? H???H? B dihydrogen interactions. The adducts can be deprotonated to give lithium amidoboranes Li[NH₂B(C₆F₅)_nH_3?n]. Reaction of the n=2 reagent with [Cp₂ZrCl₂] leads to disubstitution, but [Cp₂Zr{NH₂B(C₆F₅)₂H}₂] is in equilibrium with the product of β‐hydride elimination [Cp₂Zr(H){NH₂B(C₆F₅)₂H}], which proves to be the major isolated solid. The analogous reaction with [Cp₂HfCl₂] gives a mixture of [Cp₂Hf{NH₂B(C₆F₅)₂H}₂] and the N? H activation product [Cp₂Hf{NHB(C₆F₅)₂H}]. [Cp₂Zr{NH₂B(C₆F₅)₂H}₂] ? PhMe and [Cp₂Hf{NH₂B(C₆F₅)₂H}₂] ? 4(thf) exhibit β‐B‐agostic chelate bonding of one of the two amidoborane ligands in the solid state. The agostic hydride is invariably coordinated to the outside of the metallocene wedge. Exceptionally, [Cp₂Hf{NH₂B(C₆F₅)₂H}₂] ? PhMe has a structure in which the two amidoborane ligands adopt an intermediate coordination mode, in which neither is definitively agostic. [Cp₂Hf{NHB(C₆F₅)₂H}] has a formally dianionic imidoborane ligand chelating through an agostic interaction, but the bond‐length distribution suggests a contribution from a zwitterionic amidoborane resonance structure. Treatment of the zwitterions [Cp₂MMe(μ‐Me)B(C₆F₅)₃] (M=Zr, Hf) with Li[NH₂B(C₆F₅)_nH_3?n] (n=2) results in [Cp₂MMe{NH₂B(C₆F₅)₂H}] complexes, for which the spectroscopic data, particularly ¹J(B,H), again suggest β‐B‐agostic interactions. The reactions proceed similarly for the structurally encumbered [Cp′′₂ZrMe(μ‐Me)B(C₆F₅)₃] precursor (Cp′′=1,3‐C₅H₃(SiMe₃)₂, n=1 or 2) to give [Cp′′₂ZrMe{NH₂B(C₆F₅)_nH_3?n}], both of which have been structurally characterised and show chelating, agostic amidoborane coordination. In contrast, the analogous hafnium chemistry leads to the recovery of [Cp′′₂HfMe₂] and the formation of Li[HB(C₆F₅)₃] through hydride abstraction.     

Theoretical fluid mechanics

Experiments and Models for Young Physicists. By A. D. Bulman. (London: John Murray, 1966.) [Pp. iv + 87.] 18s.

The Velocity of Light. By J. H. Sanders. [Pp. x + 144.]

Early Electrodynamics. The First Law of Circulation. By R. A. R. Tricker. [Pp. vii + 217.]

Kinetic Theory: Volume 1. The Nature of Gases and of Heat. By S. G. Brush. [Pp. xi + 181.]

Men of Physics: Irving Langmuir. By Albert Rosenfeld. [Pp. 369.]

Phyiics is Fun. Book Three. By Jim Jardine. (London: Heinemann Educational Books Ltd., 1966.) [Pp. vii + 168.] Hard cover, 13s. 6d.; paper cover, 11s. 6d.

Transformations in Optics. By Lawrence Metz. (Wiley &; Sons, 1965.) [Pp. viii + 116.] 70s.

Relativity and Common Sense. By Hermann Bondi. (Heinemann, 1965.) [Pp. xi + 177.] 8s. 6d.

Introduction to the Theory of Relativity and the Principles of Modern Physics. Hüseyin Yilmaz. (Blaisdell Publishing Co., 135 West 50th Street, New York, 1965.) [Pp. xiv + 216.] 68s.

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Direct Generation of Electricity. Edited by K. H. Spring. (Academic Press, 1966.) [Pp. x + 410.] 105s.

Heat Bibliography. (Published for the Ministry of Technology by H.M.S.O., 1965.) [Pp. viii + 478.] £2 7s. 6d.

Physics of Quantum Electronics. By P. L. Kelley, B. Lax and P. E. Tannenwald. (McGraw Hill, Maidenhead, Berks., 1966.) [Pp. xxvii + 861.] £9 12s. Od.

Nuclear Forces. By D. M. Brink. (Pergamon, 1966.) [Pp. viii + 232.] 17s. 6d.

Physics of the Solar Corona. (2nd Edition.) By I. S. Shklovskii. (Pergamon Press, 1966.) [x + 475.] £6.

Interstellar Gas Dynamics. (2nd revised edition.) By S. A. Kaplan. (Pergamon Press, 1966.) [Pp. xii + 126.] 40s.

Quantum Mechanics. By A. S. Davydov. (Pergamon Press, 1966.) [Pp. xiii + 680.] 90s.

Radioactivity and its Measurement. By Wilfred B. Mann and S. B. Garfinkel. (Van Nostrand, 1966.) [Pp. 160.] 18s.

Nonequilibrium Thermodynamics in Physics. By A. Katchalsky and Peter F. Curran. (O.U.P., 1966.) (Source of book, Harvard University Press.) [Pp. x + 248.] 68s.

Magnetic Domains and Techniques for their Observation. By R. Carey and E. D. Isaac. (English Universities Press, 1966.) [Pp. viii + 168.] 50s.

The Quantum Equation and the Theory of Fields. By H. T. Flint. (Methuen, 1966.) [Pp. xii + 146.] 36s.

Diffraction. Coherence in Optics. By M. Françon. (Pergamon, 1966.) [Pp. ix + 139.] 20s.

Variation Principles. By B. L. Moiseiwitsch. (Wiley, 1966.) [Pp. x + 310.] 90s.

O Level Examples in Physics. By C. W. Kearsey and E. L. Clark. (Longmans Green &; Co. Ltd., 1966.) [Pp. vi + 232.] 8s.

Junction Transistors. By J. J. Sparkes. (Pergamon Press, 1966.) [Pp. viii + 249.] 25s.

Concise Applied Thermodynamics. By J. Phillips and J. B. Owen-Jones. (D. Van Nostrand Co. Ltd., 1966.) [Pp. xii + 302.] Students' edition (paper), 21s.; Library (cloth), 45s.

The Physics Teachers Handbook. By L. A. Redman. (Spectrum Books Ltd., 1966.) [Pp. 232.] 15s.

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Physics Education. (The Institute of Physics and the Physical Society.)     

Water vapor sorption in starch granules

A mathematical model proposed for diffusion in spherical particles can be solved on a digital computer. The model includes particle size distribution and variable diffusion coefficient of the form D = Doe^αC, where D is the diffusion coefficient, D₀ and α are constants, and C is the moisture content. Isothermal experimental measurements were made gravimetrically on a Cahn electrobalance by vacuum sorption techniques. The model adequately predicts the absorption characteristics of water vapor in starch granules. Although swelling is neglected in the model, it does contribute to sorption characteristics.     

Outer-sphere contributions to the electronic structure of type zero copper proteins

Bioinorganic canon states that active-site thiolate coordination promotes rapid electron transfer (ET) to and from type 1 copper proteins. In recent work, we have found that copper ET sites in proteins also can be constructed without thiolate ligation (called "type zero" sites). Here we report multifrequency electron paramagnetic resonance (EPR), magnetic circular dichroism (MCD), and nuclear magnetic resonance (NMR) spectroscopic data together with density functional theory (DFT) and spectroscopy-oriented configuration interaction (SORCI) calculations for type zero Pseudomonas aeruginosa azurin variants. Wild-type (type 1) and type zero copper centers experience virtually identical ligand fields. Moreover, O-donor covalency is enhanced in type zero centers relative that in the C112D (type 2) protein. At the same time, N-donor covalency is reduced in a similar fashion to type 1 centers. QM/MM and SORCI calculations show that the electronic structures of type zero and type 2 are intimately linked to the orientation and coordination mode of the carboxylate ligand, which in turn is influenced by outer-sphere hydrogen bonding.     

Laser-driven fast electron collimation in targets with resistivity boundary

We demonstrate experimentally that the relativistic electron flow in a dense plasma can be efficiently confined and guided in targets exhibiting a high-resistivity-core-low-resistivity-cladding structure analogous to optical waveguides. The relativistic electron beam is shown to be confined to an area of the order of the core diameter (50 μm), which has the potential to substantially enhance the coupling efficiency of electrons to the compressed fusion fuel in the Fast Ignitor fusion in full-scale fusion experiments.     

Realization of localized Bohr-like wave packets

We demonstrate a protocol to create localized wave packets in very-high-n Rydberg states which travel in nearly circular orbits around the nucleus. Although these wave packets slowly dephase and eventually lose their localization, their motion can be monitored over several orbital periods. These wave packets represent the closest analog yet achieved to the original Bohr model of the hydrogen atom, i.e., an electron in a circular classical orbit around the nucleus. The possible extension of the approach to create "planetary atoms" in highly correlated stable multiply excited states is discussed.     

Coexistence of magnetic fluctuations and superconductivity in the pnictide high temperature superconductor SmFeAsO1-xFx measured by muon spin rotation

Muon spin rotation experiments were performed on the pnictide high temperature superconductor SmFeAsO1-xFx with x=0.18 and 0.3. We observed an unusual enhancement of slow spin fluctuations in the vicinity of the superconducting transition which suggests that the spin fluctuations contribute to the formation of an unconventional superconducting state. An estimate of the in-plane penetration depth lambda ab(0)=190(5) nm was obtained, which confirms that the pnictide superconductors obey an Uemura-style relationship between Tc and lambda ab(0);(-2).     

The local determination of Jordan bases for H-self-adjoint operators

Let H be an invertible self-adjoint operator on a finite dimensional Hilbert space $\text{X}$. A linear operator A is said to be H-self-adjoint (or self-adjoint relative to H) if HA = A¹H. Let σ(A) denote, as usual, the spectrum of A. If A is H-self-adjoint, then A is similar to A¹ and λ ∈ σ(A) implies λ̄ ∈ σ (A), so that the spectrum of A issymmetric with respect to the real axis. Given spectral information for A at an eigenvalue λ₀ (≠ λ̄₀), we investigate the corresponding information at λ̄₀ and, in particular, the unique pairing of Jordan bases for the root subspaces at λ₀ and λ̄₀.