Two-amplitude model of pion DCX applied to the 18O angular distribution and excitation function

An earlier model developed to fit the DCX excitation function of ¹⁸O has been extended to account for the $\text{T}{}_{\mathrm{\pi }}\text{= 164}\text{MeV}{}^{18}\text{O DCX}$ angular distribution in terms of that for ¹⁶O and a double-isobaric-analog transition.     

Isomeric cross-section ratios in (n,t) reactions on some medium- and heavy-mass nuclei at 14.6 MeV

Cross sections were measured for the first time for the reactions ⁷⁹Br(n, t)^77mSe, ⁸⁸Sr(n, t)(^86mRb, ¹¹³In(n, t)^111mCd, ¹²⁷I(n, t)^125mTe, ¹⁴¹Pr(n, t) ^139mCe, ¹⁶⁹Tm(n, t)^167mEr and ¹⁸¹Ta(n, t)^179mHf at 14.6±0.4 MeV using the activation technique, wherever necessary radiochemical separations, and high-resolution γ-ray spectroscopy. The data lie between 10 and 120 μb. A brief review of isomeric cross-section ratios measured in (n, t) reactions is given, and the ratios are compared qualitatively with those obtained in low-energy (n, γ) reactions as well as in high-energy (n, 2n) processes. The isomeric cross-section ratios are influenced by the reaction energy available and are dependent on the spin of the isomeric state. In (n, t) reactions nuclear states with spins between $\text{3}\text{2}$ and 3 seem to be preferentially populated.     

Study of the reactions of pyridinium poly(hydrogen fluoride) with some ternary oxides

The products of the reaction of pyridinium poly(hydrogen fluoride), PPHF, with KIO₃, Na₂SnO₃, NaBiO₃, K₂CrO₄, Na₂MoO₄ and Na₂WO₄ were KIO₂F₂; Na₂SnF₆; NaHF₂, BiF₃; K₃CrF₆, KHF₂, (PyH)₃CrF₆; NaHF₂, (PyH)₂MoO₂F₄·2NaHF₂; and (PyH)₂WO₂F₄·2NaHF₂, respectively, while KClO₃, KBrO₃ and KIO₄ react with complete decomposition to form KHF₂ as the fluorinated product. This differential reactivity and mode of reaction has been discussed in terms of the oxidation state of the central atom, the nature and strength of the bonds and the complex behaviour of the formed intermediate or fluorinated products that undergo complexation or solvation with pyridine and/or hydrogen fluoride.     

Reactions of transition-metal carbonyls with anhydrous HF

The reactions of a wide range of transition-metal carbonyls with anhydrous HF are described. In particular, Ru₃(CO)₁₂, Os₃(CO)₁₂ and Ir₄(CO)₁₂ give the solution stable [Ru₃(CO)₁₂H]⁺, [Ru(CO)₅H]⁺, [Os₃(CO)₁₂H]⁺, [Os(CO)₅H]⁺ and [Ir₄(CO)₁₂H₂]²⁺ respectively, which have been characterised by a combination of ¹H and ¹³C NMR spectroscopy.     

Reactions of pentafluorophenylxenon(II) hexafluoroarsenate [C6F5Ze] [AsF6] with halide anions in acetonitrile

Reactions of [C₆F₅Xe]⁺ [AsF₆]⁻ in acetonitrile with halide anions X⁻ show different results depending on X. If X = I, Br or Cl, then C₆F₅X is obtained. If X = F, then C₆F₅H and C₆F₅---C₆F₅ are produced, and if X = HF₂, then C₆F₆, C₆F₅H and C₆F₅---C₆F₅ are formed.     

Darstellung Fluorhaltiger Hexahalogenorhenate(IV)

Preparation of Fluorine Containing Hexahalorhenates(IV) By oxidative ligand exchange on hexahalorhenates(IV) with BrF₃, KBrF₄, IF₅ and Br₂ or by substitution reactions in organic solvents as well as by solid state exchange processes 20 fluorine containing mixed ligand complexes are prepared for the first time: cis-[ReFBrI₄]^2?, fac-[ReFBr₂I₃]^2?, mer-[ReFBr₃I₂]^2?, trans-[ReFBr₄I]^2?, [ReFBr₅]^2?, trans-[ReFCl₄I]^2?, trans-[ReFCl₄Br]^2?, [ReFCl₅]^2?, cis-[ReF₂I₄]^2?, fac-[ReF₂BrI₃]^2?, all-cis-[ReF₂Br₂I₂]^2?, cis-[ReF₂BrI₂]^2?, mer-[ReF₂Br₃I]^2?, cis-[ReF₂Br₄]^2?, cis-[ReF₂Cl₄]^2?, fac-[ReF₃I₃]^2?, fac-[ReF₃BrI₂]^2?, fac-[ReF₃Br₂I]^2?, fac-[ReF₃Br₃]^2? and fac-[ReF₃Cl₃]^2?. The isolation of the pure complexes has been achieved by ion exchange chromatography on DEAE-cellulose. They are characterized by stereospecific exchange reactions in solution and by elementary analyses.     

The reaction of malononitrile with enamines of β-ketocarbothionic acid anilides

The reaction of -morpholino-thiocinnamic acid anilides1 with malononitrile yielded 2-arylimino-thiopyrans3, which in turn were converted under alkaline conditions into 6-thioxo-pyridines5. Their structures were elucidated on the basis of chemical properties and spectral data. The mechanism of the conversion3 into5 is discussed.

---

Die Reaktion von Malononitril mit Enaminen von -Ketocarbothionsäureaniliden

Zusammenfassung Die Reaktion von -Morpholino-thiozimtsäureaniliden1 mit Malononitril lieferte 2-Arylimino-thiopyrane3, die unter alkalischen Bedingungen zu 6-Thioxo-pyridinen5 umgesetzt wurden. Die Struktur der dabei erhaltenen Verbindungen wurde mittels chemischer und spektroskopischer Eigenschaften zugeordnet. Der Mechanismus der Konversion von3 zu5 wird diskutiert.

     

Monoenergetic neutron sources below 100 MeV

Monoenergetic neutron sources are essential for fundamental studies in radiobiology and dosimetry, for measurement of cross sections and kerma coefficients, for calibration of detectors, for activation analysis and for fusion research. Monoenergetic neutrons below energies of 20 MeV are most conveniently produced by reactions between the hydrogen isotopes or between protons and ⁷Li. By proper choice of reaction type monoenergetic neutrons up to 20 MeV can be produced with negligible secondary background radiation. These reactions cannot provide monoenergetic beams between about 8 and 14 MeV and in this “gap” region inverse reactions are most favourable. The most practical way of producing quasi-monoenergetic neutron beams in the energy range from 20 to 100 MeV is by the bombardment of light elements with protons. Because of the relative simplicity of manufacturing suitable isotopically-pure targets and the large 0° cross section, the ⁷Li(p,n)⁷Be reaction is a convenient source of quasi-monoenergetic neutrons over this range of energies, although the ⁹Be(p,n)⁹B reaction is also used.     

Determination of the neutron electric form factor in the D(e,e′n)p reaction and the influence of nuclear binding

The electric form factor of the neutron G _E,n has been determined at the Mainz Microtron MAMI at the low momentum transfer Q ²= 0.15 (GeV/c)² in a measurement of the recoil polarisation ratio P _x/P_z in the quasifree reaction D(e,e′n)p. At this Q ² the influence of the nuclear binding is strong. A purely kinematical model is used to get some insight into the effect of the initial Fermi momentum distribution of the neutron. The influence of the final state interaction is determined quantitatively by a model of Arenh?vel et al.. After the corresponding corrections a value of G _E,n(0.15 (GeV/c)²) = 0.0481±0.0065_stat±0.0053_syst is obtained. Received: 12 April 1999     

高分子载体Lewis酸催化剂——四氯化碲-聚苯乙烯复合物

<正> 高分子催化剂作为功能性高分子的重要组成部分具有许多独特的优点和功能,是目前催化剂研究的发展方向之一,日益受到重视。 Neckers等将AlCl_3与聚苯乙烯反应制成的高分子载体催化剂,对酯化、缩醛等反应有较好的催化作用,我们也曾制备了一系列聚苯乙烯与强Lewis酸的复合物催化剂,如聚苯乙烯-五氯化锑复合物(Ps-SbCl_5)、聚苯乙烯-四氯化钛复合物(Ps-TiCl_4)、聚苯乙烯-四氯化锡复合物(Ps-SnCl_4)、聚苯乙烯-三氯化铁复合物(Ps-FeCl_3)等,它们具有较高的稳定性和良好的催化效能.为了研究弱Lewis酸与高分子载体的复合能力以及它们是否还具有催化活性,为了研究各种Lewis酸用高分子载体固载化的规律