Observation of in-medium modifications of the omega meson

The photoproduction of omega mesons on nuclei has been investigated using the Crystal Barrel/TAPS experiment at the ELSA tagged photon facility in Bonn. The aim is to study possible in-medium modifications of the omega meson via the reaction gamma + A --> omega + X --> pi(0)gamma + X('). Results obtained for Nb are compared to a reference measurement on a LH2 target. While for recoiling, long-lived mesons (pi(0), eta, and eta;(')), which decay outside of the nucleus, a difference in the line shape for the two data samples is not observed, we find a significant enhancement towards lower masses for omega mesons produced on the Nb target. For momenta less than 500 MeV/c an in-medium omega meson mass of M(medium) = [722(+4)(-4)(stat)+35-5(syst)] MeV/c(2) has been deduced at an estimated average nuclear density of 0.6rho(0).     

Photoproduction of eta mesons off protons for 0.75 GeV<E(gamma)<3 GeV

Total and differential cross sections for the reaction p(gamma,eta)p have been measured for photon energies in the range from 750 MeV to 3 GeV. The low-energy data are dominated by the S11 wave which has two poles in the energy region below 2 GeV. Eleven nucleon resonances are observed in their decay into peta. At medium energies we find evidence for a new resonance N(2070)D15 with (M,Gamma)=(2068+/-22, 295+/-40) MeV. At gamma energies above 1.5 GeV, a strong peak in the forward direction develops, signaling the exchange of vector mesons in the t channel.     

Photoproduction of π 0 ω off protons for E γ ≤3 GeV

Differential and total cross-sections for photoproduction of γp→pπ ⁰ ω and γp→Δ ⁺ ω were determined from measurements of the CB-ELSA experiment, performed at the electron accelerator ELSA in Bonn. The measurements covered the photon energy range from the production threshold up to 3GeV.     

Untersuchungen über N-(Trichlormethylcarbimidoyl)guanidin. 1. Konformationsuntersuchungen am Molekül und am Kation

Studies on N-(Trichlormethylcarbimidoyl)guanidine. 1. Conformation Studies on the Molecule and its Cation On the foundation of infrared, nuclear magnetic resonance, and mass spectra the conformations of the title compound TCG (formula see ?Inhaltsübersicht”?) and of its cation [TCGH]⁺ have been studied in solid state, in solution, and in gaseous state. The free base and the cation have in solution the common endiamine structural fragment ? N?C(NH₂)₂. In solution the amino protons are involved in rapid interchange processes. The activation parameters of the interchanges have been approximately determined from temperature dependent ¹H-NMR experiments.     

Reassessment of the electronic absorption spectra of Cr(η6-C6H6)2, Cr(CO)6 and Cr(η6-C6H6)(CO)3

The UV absorption bands between approximately 330 and 200 nm have been assigned to Rydberg transitions for the d⁶ complexes Cr(η⁶-C₆H₆)₂, Cr(CO)₆ and Cr(η⁶-C₆H₆)(CO)₃     

Über Chalkogenolate. 196. Untersuchungen über N-(Methoxycarbimidoyl)guanidin 2. Umsetzungen mit Chlordithioameisensäureestern

On Chalcogenolates. 196. Studies on N-(Methoxycarbimidoyl)guanidine. 2. Reactions with Esters of Chlorodithioformic Acid N-(Methoxycarbimidoyl)guanidine reacts with esters of chlorodithioformic acid to produce the hitherto not known esters of N-(Methoxycarbimidoyl)guanidinedithiocarbonic acid (MCGT-R; formula see ?Inhaltsübersicht”?). By-product is the corresponding 2-amino-4-methoxy-6-alky(aryl)thio-1,3,5-triazine. MCGT-R, where R = CH₃, C₂H₅, C₆H₅, have been characterized by means of electron absorption, infrared, nuclear magnetic resonance, and mass spectra. The spectra and the related tautomeric structures of the dithioesters are discussed.     

Über Chalkogenolate. 166. Umsetzungen von Hydrazin mit Kohlenstoffdisulfid 5. Versuche zur Darstellung von Estern der 1,2-Hydrazin-bis(dithiocarbonsäuren) [1]

On Chalcogenolates. 166. Reactions of Hydrazine with Carbon Disulfide. 5. Attempts to Prepare Esters of 1,2-Hydrazine-bis(dithiocarboxylic Acids) Possible reactions to synthesize esters of 1,2-hydrazine-bis(dithiocarboxylic acids) are described:

• 1 The reaction of K₂[S₂C? NH? NH? CS₂] with H₃CI preponderantly forms 2,5-dimethylthio-1,3,4-thiadiazole Ia and a small quantity of bis(methylthio)-ketazine II (formula see ?Inhaltsübersicht”?).
• 2 Hydrazine reacts with Cl? CS? SC₂H₅ to give exclusively compound Ib
• 3 The reaction between K₂[S₂C=N? NH? CS? SCH₃] and H₃CI yields 94% compound Ia and 6% compound II
• 4 K₂[S₂C=N? NH? CS? SCH₃] reacts with C₆H₅? CH₂Br to form a mixture containing 25% dibenzyl sulfide, 15% 2,5-dibenzylthio-1,3,4-thiadiazole I e, and 60% 2-methylthio-5-benzylthio-1,3,4-thiadiazole I d

The compounds Ia , Id and II have been characterized by means of diverse spectroscopic methods. The mechanism of the formation of compounds I has been discussed.     

Helical Polyacetylene‐Based Switchable Chiral Columnar Phases: Frustrated Chain Packing and Two‐Way Shape Actuator

Chiral columns formed by a helical cis‐polyphenylacetylene (PPA) derivative P1 are reversibly switched during a phase transition between two chiral columnar phases: the frustrated Φ_h^3D‐SL phase containing four chains at low temperature and a hexagonal columnar phase Φ_h at high temperature, accompanied by a simultaneous conformational change. The helix–helix transition along the PPA backbone during the Φ_h^3D‐SL‐Φ_h transition makes the uniaxially oriented P1 capable of reversibly and reproducibly elongating (132 %) upon heating and contracting upon cooling, exhibiting the behavior of a two‐way shape actuator.     

Quasifree photoproduction of eta mesons off the neutron

Quasifree photoproduction of eta mesons off nucleons bound in the deuteron has been measured with the CBELSA/TAPS detector for incident photon energies up to 2.5 GeV at the Bonn ELSA accelerator. The eta mesons have been detected in coincidence with recoil protons and recoil neutrons, which allows a detailed comparison of the quasifree n(gamma,eta)n and p(gamma,eta)p reactions. The excitation function for eta production off the neutron shows a pronounced bumplike structure at W=1.68 GeV (E{gamma} approximately 1 GeV), which is absent for the proton.