Quasi-fission — The mass-drift mode in heavy-ion reactions

The binary and ternary products from reactions of ²³⁸U beams with targets of ¹⁶O, ²⁷Al, ⁴⁸Ca, ⁴⁵Sc, ⁴⁸Ti, ⁵⁸Fe, ⁶⁴Ni and ⁸⁹Y have been recorded at 6.0 MeV/u bombarding energy with four position-sensitive avalanche detectors, operated in coincidence. A few runs at 5.4 MeV/u have also been performed. Accurate triple-differential cross sections, $\text{d}{}^3\text{σ}\text{d}\text{A}\text{d}\text{θ}{}_{\mathrm{<mtext>c.m.</mtext>}}\text{dTKE}$, are obtained for the binary events within the full range of mass A and total kinetic energy TKE, and within almost the full range of center-of-mass angle θ_c.m.. Similar cross sections are obtained with somewhat less accuracy for triple events stemming from the sequential fission of uranium-like products. The distributions are discussed in terms of quasielastic and strongly damped scattering, where the products have partially relaxed energies and negligible average drift in mass, as opposed to capture where the products emerge with fully relaxed energies after a more or less pronounced mass drift towards symmetry. Apart from the reaction with ¹⁶O, all the capture product distributions are dominated by the non-equilibrium quasi-fission (or fast fission) process. The central feature of this reaction mechanism is the evolution of the reaction complex towards mass symmetry. With the ²⁷Al target the evolution towards symmetry is almost complete, whereas the heavier targets show very broad mass distributions with clear evidence of dissociation taking place before symmetry is reached. At the same time, the cross section for quasi-fission diminishes as the target Z-value increases. With the ⁸⁹Y target the strongly damped scattering component dominates completely. The capture cross sections are discussed in terms of the extra-push concept, and the mass and angular distributions in quasi-fission are analyzed in terms of interaction time and mass rearrangement as functions of target Z-value and excess kinetic energy in the entrance channel.     

Channel spin mixing ratios in high resolution proton inelastic scattering

A simple method of determining both the magnitudes and phase for channel spin mixing is described. An example is presented and a variety of applications discussed.     

Ziegler-Natta-Katalysatoren. 11. Mitt. Kinetik des Metathese-Abbaues von teilweise chloriertem Polybutadien

Ohne Zusammenfassung     

Reaktionen koordinierter Liganden. IX [1]. Reaktionen und Molekülstruktur von Tetracarbonyl(1,1,2,3,3-pentaphenyltriphosphan-P2)eisen(0) – einem Monosubstitutionsprodukt des Pentacarbonyleisens mit äquatorialem Phosphanliganden

Die Struktur von Tetracarbonyl(1,1,2,3,3-pentaphenyltriphosphan-P²)-eisen(0) ( I ) wurde röntgenographisch bestimmt. I kristallisiert in der Raumgruppe P1 . Es weist trigonal bipyramidale Koordination am Fe-Atom auf. Der Phosphanligand befindet sich in äquatorialer Position mit einem Fe? P? ;Abstand von 226,2(1) pm. Der mittlere Abstand Fe? C für die axial gebundenen CO-Gruppen beträgt 178,8(3) pm und unterscheidet sich nicht signifikant von dem für die äquatorial gebundenen CO-Gruppen. Die P? P? Abstände im Triphosphanliganden unterscheiden sich um 1,9 pm [225,6(2) und 223,7(1) pm]. Mit PtCl₂ bildet I einen Komplex ( III ) der Zusammensetzung (CO)₄FePPh(PPh₂)₂PtCl₂, in dem die terminalen Phosphoratome an das Platin koordiniert sind und einen viergliedrigen Ring bilden. Beim Erhitzen lagert sich I unter Wanderung der Fe(CO)₄-Einheit von der medialen in die terminale Position der Triphosphankette in den isomeren Komplex II um. Die Bestrahlung von I mit UV-Licht liefert als Hauptprodukte Ph₂P? PPh₂ und (CO)₄Fe? PPhH? PPh₂. Reactions of Coordinated Ligands. IX. Reactions and Molecular Structure of Tetracarbonyl(1,1,2,3,3-pentaphenyltriphosphane-P²)iron(0) – a Monosubstitution Product of Pentacarbonyliron with an Equatorial Phosphane Ligand The structure of tetracarbonyl(1,1,2,3,3-pentaphenyltriphosphane-P²)iron(0) (I) was determined by X-ray analysis. The molecule displays a trigonal-bipyramidal coordination geometry at the iron atom with the phosphane ligand in an equatorial position and an Fe? P distance of 226.2(1) pm. The average Fe? C axial distance of 178.8(3) pm is not significantly different from that of 178.0(5) pm for the average Fe? C equatorial distance. A difference of 1.9 pm is observed between the two P? P distances [225.6(2) and 223.7(1) pm]. With PtCl₂ I yields a complex of composition (CO)₄FePPh(Ph₂P)₂PtCl₂ (III) in which the terminal phosphorus atoms of I are coordinated to platinum forming a four membered ring system. On heating, complex II , an isomer of I , is formed by migration of the Fe(CO)₄-unit from the medial to the terminal position within the triphosphane chain. Irradiation of I with UV light affords Ph₂P? PPh₂ and Fe(CO)₄? PPhH? PPh₂ as main products.     

Water-soluble phosphines. 17.(1) novel water-soluble secondary and tertiary phosphines with disulfonated 1,1'-biphenyl backbones and dibenzophosphole moieties

Reaction of 2,2'-difluoro-1,1'-biphenyl with chlorosulfonic acid and subsequent hydrolysis followed by neutralization with potassium or sodium hydroxide affords disodium or dipotassium 5,5'-disulfonato-2,2'-difluoro-1,1'-biphenyl (1a, 1b). On treatment of 1b with diphenyl- or phenylphosphine in the superbasic medium DMSO/KOH, phosphine ligand 2 or 3 with a disulfonated 1,1'-biphenyl backbone or a dibenzophosphole moiety is formed. The structure of the oxide of 5-phenyldibenzophosphole 3, which crystallizes as 4.2.5H(2)O in the monoclinic space group P2(1)/n with a = 13.799(3) A, b = 19.246(4) A, c = 17.764(4) A, beta = 105.63(3) degrees, and Z = 4, has been determined by X-ray analysis. Nucleophilic phosphination of 1a with NaPH(2) in liquid ammonia yields the sodium phosphide 5a which on protonation gives the water-soluble 5H-dibenzophosphole 5. Reaction of 1b with PH(3) in the superbasic medium DMSO/KOtBu affords 5b in addition to the oxidation product 6a. On oxidation of 5a or 5b with H(2)O(2), the sodium or potassium salts of the sulfonated phosphinic acids 6a or 6b, respectively, are formed. Alkylation of the sodium dibenzophospholide 5a with 2,2'-bis(chloromethyl)-1,1'-biphenyl or 1,4-di-O-p-toluenesulfonyl-2,3-O-isopropylidene-D-threitol yields the chiral water-soluble bidentate phosphine ligands 8 and 9, respectively.     

Some aspects of the synthesis and characterization of special polymers and oligomers by olefin metathesis

Homopolymers of 2-norbornene and 2,3-bis(trifluoromethyl)-2,5-norbornadiene and copolymers of these bicyclic olefins with 1,5-cyclooctadiene and cyclopentene were prepared via ring opening metathesis polymerization. The molecular weight distributions of the polymers were estimated by gel permeation chromatography.The polymers were degraded in a cross metathesis reaction with E-4-octene; only poly[2,3-bis(trifluoromethyl)-2,5-norbornadiene] was not degradable.All reactions were carried out with WCl₆/(CH₃)₄Sn as the catalyst system. The low molecular cyclic oligomers in the polymerization mixtures and the degradation products were analyzed by gas chromatography and identified using a gas chromatography/mass spectrometry coupling.The degradation experiments show reactivity differences for the double bonds situated in the polymer backbone. On the basis of these differences and the fact that this is the first time that a metathesis degradation of such polymers has been reported, the consequences on the ring opening metathesis copolymerization of cycloolefins are discussed in general terms, leading to some new aspects in the planning of the synthesis of special copolymers and oligomers.With reference to a lecture presented at the 4th International Symposium on Olefin Metathesis (ISOM 4), Belfast, 1–4 Sept. 1981.     

η3:η1⇌η2-tautomerism in carbonyliron complexes. Thermodynamic characteristics

The thermodynamic characteristics of the equilibrium between the chelate tricarbonylmethyl-π-allyl-σ-R-carbamoyliron complex (R = c-C₆H₁₁) and its π-olefinic isomer in hexane and in hexane/dichloromethane were determined. The observed values fit fairly well with the thermodynamic scale of tautomerism and allow a quantitative conclusion on the influence of solvent, temperature and polarity on the relative stabilities of the tautomeric forms to be reached.