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  • 1
    Electronic Resource
    Electronic Resource
    Production of medium-weight isotopes by fragmentation in 750 A MeV 238U on 208Pb collisions (1998)
    Springer
    The European physical journal 2 (1998), S. 193-198 
    Details
    ISSN: 1434-601X
    Keywords: PACS:25.75.-q – 25.70.Mn – 21.10.Ft – 21.10.Gv – 27.50.+e – 27.50.+j – 24.10.Pa
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract: Projectile fragmentation of 238U in a lead target was investigated at a bombarding energy of 750 A MeV. Isotopic production cross sections of about 250 different projectile fragments in the element range Z= 30–53 were measured with the FRagment Separator (FRS). The magnetic selection and the kinematical analysis of the measured isotopes allowed to disentangle fission and fragmentation residues. The mass loss of these residues indicates a violent collision where a large amount of energy is dissipated. The position of the fragmentation corridor defined by the measured residues was used to determine an effective proton-evaporation barrier.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s100500050108
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  • 2
    Electronic Resource
    Electronic Resource
    Fission of highly excited fragments from collisions of 750 A.MeV 238U-ions on 208Pb (1998)
    Springer
    The European physical journal 2 (1998), S. 179-191 
    Details
    ISSN: 1434-601X
    Keywords: PACS:25.85.-w Fission reactions – 25.75.-q Relativistic heavy-ion collosions
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract: Fragments of relativistic 750 A.MeV U-projectiles were investigated by using the fragment separator FRS for magnetic selection of reaction products including ray-tracing and ΔE-ToF techniques. For elements between Ge and Sb, measurements of isotopic yield distributions and velocities revealed three processes: fragmentation, low-energy fission, and high-energy fission. The last of these regimes is presently reported. First and second moments of distributions of mass numbers, atomic numbers and velocities of the corresponding fragments allowed us to identify 101 43Tc56 as the most probable fragment of a high energy symmetric fission reaction. Moreover, we could deduce a hypothetical mean fissioning fragmentation product 208Rn and its highly excited pre-fragmentation parent 227Ra produced in a primary abrasion reaction at an excitation energy of about 290 MeV.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s100500050107
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  • 3
    Electronic Resource
    Electronic Resource
    β-decay half-lives of very neutron-rich isotopes of elements from Ti to Ni (1998)
    Springer
    The European physical journal 1 (1998), S. 275-283 
    Details
    ISSN: 1434-601X
    Keywords: PACS:23.40.-s β decay, double β decay, electron and muon capture – 27.30.+t 20 ≤ A ≤ 38 – 27.50.+e 59 ≤ A ≤ 89
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract: The unknown β-decay half-lives of 22 isotopes far off stability (5 〈 T Z 〈 10) in the region from Ti to Ni were measured at GSI, Darmstadt. The nuclei were produced in a fragmentation reaction of 500 A.MeV 86Kr-projectile impinging on a thick Be target. The isotopes of interest were separated and identified with the fragment separator, FRS, by a combination of Bρ,Z, and ToF techniques. An additional range separation was performed by a selective implantation into granular detectors. The spatial and time correlations of the implant with the consecutively detected β-particles were used to determine the unknown half-lives. For nuclei far off stability, β-decay chains were measured and analyzed as well, leading to an even more reliable evaluation of the lifetimes. The large discrepancies found between the measured and the theoretical values emphasize that most recent theoretical work is not an improvement over calculations made almost a decade ago.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s100500050062
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  • 4
    Electronic Resource
    Electronic Resource
    Low-energy fission investigated in reactions of 750 AMeV 238U-ions on 208Pb. II: Isotopic distributions (1998)
    Springer
    The European physical journal 1 (1998), S. 407-426 
    Details
    ISSN: 1434-601X
    Keywords: PACS:25.85.-W Fission reactions
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract: Projectile fission of 750 AMeV 238U-ions interacting with a Pb target was studied by means of the spectrometer FRS, GSI-Darmstadt. One of the two fission fragments was detected with a transmission of few percent and identified in mass and charge. Low-energy fission (E* 〈 25 MeV) events were selected by their magnetic rigidity. Whereas the production of asymmetric fission events is dominated by the GDR excitation, very asymmetric fission and symmetric fission take place after a GQR or DGDR excitation or after a nuclear interaction. Cross sections of more than 250 isotopes were measured. Isotopic distributions of low-energy fission were reconstructed for elements from Se to Te. The fission modes SI, SII and SL were clearly shown in these distributions and in the mass and TKE distributions. Charge polarization and mass dispersion were deduced for each fission mode. Finally, the characteristics of the low-energy fission process explain the production rates of neutron-rich species.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s100500050076
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  • 5
    Electronic Resource
    Electronic Resource
    [2.2]Paracyclophane-4,7,12,15-tetrone, [2.2](1,4)Naphthalenophane-4,7,14,17-tetrone, and 1,4,8,11-Pentacenetetrone Radical Anions - A Comparative ESR Study (1998)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1998 (1998), S. 221-227 
    Details
    ISSN: 1434-193X
    Keywords: 1,4-Benzoquinones ; [2.2]Paracyclophanes ; 1,4,8,11-Pentacenetetrones ; Cyclic voltammetry ; Radical anions ; ESR/ENDOR spectroscopy ; Intramolecular electron transfer ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Three types of tetrone radical anions in which two 1,4-benzoquinone units are connected by ethano (1·-, 2·-), [2.2]paracyclophane (3·-, 4·-), and anthracene bridges (5·-, 6·-) have been studied by ESR and ENDOR spectroscopy. The displacement of the unpaired electron over the two π moieties in the [2.2]cyclophane radical anions 1·--4·- and the marked difference between the first and second reduction potentials, ΔE = |E20 - E10| ≥ 0.20 V, are evidence for a substantial intramolecular electronic interaction between the two electrophores. Similar ΔE data for the syn- (3) and anti-naphthalenophanes (4) indicate that most of the intramolecular electronic interaction takes place through the [2.2]paracyclophane bridge. When ion pairing is inhibited by complexation of the cation, the unpaired electron in 5·- and 6·- is also delocalized over the whole pentacenetetrone system at temperatures as low as 160 K.
    Type of Medium: Electronic Resource
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  • 6
    Electronic Resource
    Electronic Resource
    Distance Dependence of Photoinduced Electron Transfer: Syntheses and Properties of Anthracene-Spacered Porphyrin-Quinone Cyclophanes (1998)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1998 (1998), S. 631-642 
    Details
    ISSN: 1434-193X
    Keywords: Electron transfer, distance dependence of ; Anthracene-spacered porphyrin-quinone cyclophanes ; Syntheses ; Characterizations ; Structures ; Physical properties ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: In our previous work on benzene- and naphthalene-spacered porphyrin-quinone cyclophanes[1][2], the dependence of electron-transfer rates on reduction potentials of the acceptors and oxidation potentials of the porphyrins was studied. The present paper, dealing with the distance dependence of electron transfer, reports on the synthesis of anthracene-spacered analogues and on the electron-transfer rates, which are found to be drastically reduced.
    Type of Medium: Electronic Resource
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  • 7
    Electronic Resource
    Electronic Resource
    Intramolecular Electron Transfer between 2,5-Dimethoxy-1,4-phenylene Units in [n.n]Paracyclophane Radical Cations (1998)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1998 (1998), S. 139-148 
    Details
    ISSN: 1434-193X
    Keywords: Paracyclophanes ; Cyclic voltammetry ; Radical cations ; ESR/ENDOR spectroscopy ; Intramolecular electron transfer ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A range of [n.n]paracyclophane radical cations (4·+-12·+), in which two 2,5-dimethoxy-1,4-phenylene units are connected by alkano bridges of varying length, have been studied by ESR and ENDOR spectroscopy. In the [2.2]- and [3.3]paracyclophane radical cations 4·+-6·+, 10·+ and 11·+ the delocalization of the unpaired electron over both π-moieties and the distinct difference between the first and second oxidation potentials, ΔE = E20 - E10, are evidence for a strong intramolecular electronic interaction between the two electrophores. The [5.5] and [7.7] species (8·+ and 9·+) are localized radical cations at low temperature (ca. 220 K). At room temperature, the higher molecular flexibility leads to a significant increase in the number of internal collisions between the electrophores, resulting in a fast (ESR time scale) intramolecular electron transfer. The intermediate [4.4]paracyclophane radical cations 7·+ and 12·+ are apparently also localized radical cations. The close interplanar distance between the two π-moieties, however, facilitates their mutual contacts. In 7·+, the intramolecular electron transfer becomes fast on the ESR time scale at room temperature; in 12·+ the transfer is fast over the temperature range 200-300 K.
    Type of Medium: Electronic Resource
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  • 8
    Electronic Resource
    Electronic Resource
    Distance Dependence of Photoinduced Electron-Transfer: Syntheses and Properties of Biphenylene-Spacered Porphyrin-Quinone Cyclophanes (1998)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1998 (1998), S. 2149-2160 
    Details
    ISSN: 1434-193X
    Keywords: Porphyrin-quinone systems ; Biphenylene-spacered cyclophanes ; Syntheses, structures, spectroscopic properties ; Electron-transfer rates, distance dependence of ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: In continuation of previous syntheses of benzene-, naphthalene-, and anthracene-spacered porphyrin-quinone cyclophanes 1, 2, and 4, biphenylene-spacered porphyrin-quinone cyclophanes of structure 3 as the “missing link” between 2 and 4 were prepared in multistep syntheses. These donor-acceptor systems are of interest since, with regard to electron-transfer rates, they complete the series of 1, 2, and 4. As expected the electron-transfer of 3 proceeds between that of 2 and 4 in an especially steep region of distance dependences of electron-transfer rates.
    Type of Medium: Electronic Resource
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  • 9
    Electronic Resource
    Electronic Resource
    Porphyrin-Cyclophanes with 7,7,8,8-Tetracyanoquinodimethane as an Especially Strong Electron-Acceptor: Syntheses, Properties, Electron-Transfer Interactions (1998)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1998 (1998), S. 2703-2711 
    Details
    ISSN: 1434-193X
    Keywords: Porphyrin-acceptor cyclophanes ; 7,7,8,8-Tetracyanoquinodimethane (TCNQ)-bridged porphyrins ; Electron-transfer-related properties ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Previous work on intramolecular electron-transfer compounds of the quinone-porphyrin cyclophane type with gradually increasing electron-acceptor strength was now extended to acceptor-porphyrin cyclophanes with 7,7,8,8-tetracyanoquinodimethane (TCNQ) as an especially strong electron-acceptor. The vertically stacked TCNQ-porphyrin cyclophane 1 was prepared in a multi-step synthesis. Physical properties related to structure and electron-transfer processes of 1 are reported. To determine the distance dependence of the interaction between the electron-acceptor TCNQ and the porphyrin, first results on the synthesis of the corresponding naphthalene-spacered TCNQ-porphyrin cyclophane 15 are presented.
    Type of Medium: Electronic Resource
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  • 10
    Electronic Resource
    Electronic Resource
    Intramolecular Electron Transfer between Terminal 1,4-Dimethoxybenzene Units in Radical Cations with a [2.2](1,4)Naphthalenophane, [2.2](1,4)Anthracenophane, and Pentacene Skeleton (1998)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1998 (1998), S. 1161-1170 
    Details
    ISSN: 1434-193X
    Keywords: [2.2](1,4)Naphthalenophanes ; [2.2](1,4)Anthracenophane ; Pentacene ; Cyclic voltammetry ; Radical cations ; ESR/ENDOR spectroscopy ; Intramolecular electron transfer ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Various radical cations, in which two terminal 1,4-dimethoxybenzene units are anellated to [2.2]paracyclophane (2b•+, 3b•+), [2.2](1,4)naphthalenophane (4d•+), and anthracene bridges (5•+), have been studied by ESR and ENDOR spectroscopy. In the syn- and anti-naphthalenophane radical cations 2b•+ and 3b•+ the delocalization of the unpaired electron over both π-moieties and the distinct difference between the first and second oxidation potentials, ΔE = E20 - E10, are evidence for a substantial intramolecular electronic interaction between the two electrophores. Extension of the bridge in 4d•+ and 5 by benzo anellation results in a localized radical cation. Strong intramolecular electronic interaction between the two electrophores is found in the 1,4,8,11-tetramethoxy-pentacene radical cation (5•+). The syntheses of 4d are described.
    Type of Medium: Electronic Resource
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