Semiquantitative estimates of currents generated by monochromatic waves in toroidal plasmas

Landau damping and transit time damping are analyzed from the point of view of toroidal electric current generation. Steady current density and energy absorption are estimated. The importance of momentum transfer to non-resonant electrons via Coulomb collisions is pointed out. If the bounce period of trapped electrons is less than their collisional relaxation time, the most part of the toroidal current is generated due to collisional dragging of non-resonant electrons.The author gratefully acknowledges valuable discussions with K.Jungwirth, V.Kopecký, V. L.Sizonenko and K. N.Stepanov.     

The tensor of time-averaged stresses for plasma with an oscillating field

The tensor of time-averaged stresses arising in a plasma under the effect of a magnetostatic and an oscillating field is derived. The plasma is assumed to be collisionless, quasineutral, the particle velocities being far smaller than the wave phase velocities. The case of cyclotron resonance is excluded. The resultant tensor is proved to be symmetric.     

5-Halogenierte N-Hydroxypyrimidine

Zusammenfassung Es wird die 5-Halogenierung der isomeren N-Benzyloxy- und N-Hydroxyuracile beschrieben. Die Einwirkung von 2 Mol Chlor auf 1-Benzyloxyuracil, gefolgt von milder alkalischer Hydrolyse, führt zu Ringspaltung. Das 5-Fluor-1-hydroxyuracil (18) wird auf drei verschiedenen Wegen erhalten, wobei eine neue Variante eines Pyrimidinringschlusses verwendet wird. Das 3-Hydroxy-5-fluorcytosin (21) wird durch Persäureoxydation von 2-Chlor-4-amino-5-fluorpyrimidin und nachfolgende Hydrolyse erhalten. Essiganhydrid lagert es um in 4-Acetoxyamino-5-fluor-2-oxodihydropyrimidin (23). Die Desaminierung von (21) zum isomeren 3-Hydroxy-5-fluoruracil gelang nicht.

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The halogenation of the isomeric N-benzyloxy- and N-hydroxyuracils in position 5 is described. Treatment of benzyloxyuracil with 2 moles Cl₂ followed by mild alkaline hydrolysis causes ring cleavage. 1-Hydroxy-5-fluorouracil (18) can be obtained by three different methods including a new cyclization reaction. 3-Hydroxy-5-fluorocytosin (21) was prepared by peracid oxidation of 2-chloro-4-amino-5-fluoropyrimidine and subsequent hydrolysis. With acetic anhydride the latter rearranges to give 4-acetoxyamino-5-fluoro-2-oxodihydropyrimidine (23). Deamination of21 to the isomeric 3-hydroxy-5-fluorouracil is not feasible.

     

Zn adsorption on Pd(111): ZnO and PdZn alloy formation

The adsorption and thermal desorption of Zn and ZnO on Pd(111) was studied in the temperature range between 300 and 1300 K with TDS, LEED, and CO adsorption measurements. At temperatures below 400 K, multilayer growth of Zn metal on the Pd(111) surface takes place. At a coverage of 0.75 ML of Zn, a p(2 x 2)-3Zn LEED structure is observed. Increasing the coverage to 3 ML results in a (1 x 1) LEED pattern arising from an ordered Zn multilayer on Pd(111). Thermal desorption of the Zn multilayer state leads to two distinct Zn desorption peaks: a low-temperature desorption peak (400-650 K) arising from upper Zn layers and a second peak (800-1300 K) originating from the residual 1 ML Zn overlayer, which is more strongly bound to the Pd(111) surface and blocks CO adsorption completely. Above 650 K, this Zn adlayer diffuses into the subsurface region and the surface is depleted in Zn, as can be deduced from an increased amount of CO adsorption sites. Deposition of >3 ML of Zn at 750 K leads to the formation of a well-ordered Pd-Zn alloy exhibiting a (6 x 4 square root 3/3)rect. LEED structure. CO adsorption measurements on this surface alloy indicate a high Pd surface concentration and a strong reduction of the CO adsorption energy. Deposition of Zn at T > 373 K in 10(-6) mbar of O2 leads to the formation of an epitaxial (6 x 6) ZnO overlayer on Pd(111). Dissociative desorption of ZnO from this overlayer occurs quantitatively both with respect to Zn and O2 above 750 K, providing a reliable calibration for both ZnO, Zn, and oxygen coverage.     

Spatially resolved dynamic eigenmode spectrum of Co rings

The spatially resolved eigenmode spectrum of micrometer-sized Co ring elements has been determined by means of combined vector network analyzer ferromagnetic resonance and time resolved magneto-optic Kerr effect measurements. Up to 5 resonant eigenmodes were observed in the frequency range from 45 MHz to 20 GHz as a function of an external magnetic bias field. A well-defined mode structure was found for the two equilibrium states (vortex and onion) which correspond to distinctive spatial modes. The effect of dynamic inter-ring coupling on the modes in the remanent states was evinced. The experimental results are found to be in good agreement with those of micromagnetic simulations. Our results demonstrate that, in analogy to the well-defined static equilibrium magnetic states of ring elements, the eigenmode spectra of this high symmetry geometry consist of a well-defined and simple mode structure.     

Fluorescence and REMPI spectroscopy of jet-cooled isolated 2-phenylindene in the S1 state

We investigated the spectroscopy of the first excited singlet electronic state S1 of 2-phenylindene using both fluorescence excitation spectroscopy and resonantly enhanced multiphoton ionization spectroscopy. Moreover, we investigated the dynamics of the S1 state by determining state-selective fluorescence lifetimes up to an excess energy of approximately 3400 cm(-1). Ab initio calculations were performed on the torsional potential energy curve and the equilibrium and transition state geometries and normal-mode frequencies of the first excited singlet state S1 on the CIS level of theory. Numerous vibronic transitions were assigned, especially those involving the torsional normal mode. The torsional potentials of the ground and first excited electronic states were simulated by matching the observed and calculated torsional frequency spacings in a least-squares fitting procedure. The simulated S1 potential showed very good agreement with the ab initio potential calculated on the CIS/6-31G(d,p) level of theory. TDDFT energy corrections improved the match with the simulated S(1) torsional potential. The latter calculation yielded a torsional barrier of V2 = 6708 cm(-1), and the simulation a barrier of V2 = 6245 cm(-1). Ground-state normal-mode frequencies were calculated on the B3LYP/6-31G(d,p) level of theory, which were used to interpret the infrared spectrum, the FDS spectrum of the transition and hot bands of the FES spectrum. The fluorescence intensities of the nu49 overtone progression could reasonably be reproduced by considering the geometry changes upon electronic excitation predicted by the ab initio calculations. On the basis of the torsional potential calculations, it could be ruled out that the uniform excess energy dependence of the fluorescence lifetimes is linked to the torsional barrier in the excited state. The rotational band contour simulation of the transition yielded rotational constants in close agreement to the ab initio values for both electronic states. Rotational coherence signals were obtained by polarization-analyzed, time-resolved measurements of the fluorescence decay of the transition. The simulation of these signals yielded corroborating evidence as to the quality of the ab initio calculated rotational constants of both states. The origin of the anomalous intensity discrepancy between the fluorescence excitation spectrum and the REMPI spectrum is discussed.     

Carbon incorporation in Pd(111) by adsorption and dehydrogenation of ethene

The decomposition of ethene on the Pd(111) surface was studied at effective pressures in the 10(-8) to 10(-7) mbar range and at sample temperatures between 300 and 700 K, using an effusive capillary array beam doser for directional adsorption, LEED, AES, temperature programmed reaction, and TDS. In the temperature range of 350-440 K increasingly stronger dehydrogenation of the ethene molecule is observed. Whereas at 350 K an ethylidyne adlayer is still present after adsorption, already at temperatures around 440 K complete coverage of the surface by carbon is attained, while the bulk still retains the properties of pure Pd. Beyond 440 K a steady-state surface C coverage is established, which decreases with temperature and is determined by detailed balancing between the ethene gas-phase adsorption rate and the migration rate of carbon into the Pd bulk. This process gives rise to the formation of a "partially carbon-covered Pd(x)C(y) surface". Above 540 K the surface-bulk diffusion of adsorbed carbon becomes fast, and in the UHV experiment the ethene adsorption rate becomes limited by the ethene gas-phase supply. The carbon bulk migration rate and the steady-state carbon surface coverage were determined as a function of the sample temperature and the ethene flux. An activation energy of 107 kJ mol(-1) for the process of C diffusion from surface adsorption sites into the subsurface region was derived in the temperature range of 400-650 K by modeling the C surface coverage as a function of temperature on the basis of steady-state reaction kinetics, assuming a first-order process for C surface-subsurface diffusion and a second-order process for C(ads) formation by dissociative C2H4 adsorption.     

Originalarbeiten: Radiogaschromatographische Untersuchungen an flüchtigen Photolyseprodukten des Systems Bis-(tributylzinn)-oxid-(butyl-1-14C)/Cellulose

Es werden Apparatur und Methode zur radiogaschromatographischen Trennung und Identifizierung von Photolyseprodukten des Systems Bis-(tributylzinn)-oxid-(butyl-1-¹⁴C)/Cellulose beschrieben. Dabei wurde nachgewiesen, daβ beim UV-induzierten Abbau dieses Systems u. a. n-Butan-¹⁴C und n-Octan-¹⁴C gebildet werden. Die von der Organozinnverbindung abgespaltenen ¹⁴C-markierten Butylradikale stabilisieren sich demnach durch Reaktion mit Wasserstoffatomen ( Photolyseprodkt der Cellulose) und durch Dimerisierung.     

Universal integrability objects

We discuss the main points of the quantum group approach in the theory of quantum integrable systems and illustrate them for the case of the quantum group U_q(L(sl ₂ )). We give a complete set of the functional relations correcting inexactitudes in the previous considerations. We especially attend to the interrelation of the representations used to construct the universal transfer operators and Q-operators.