Laser systems specialized for laser spectroscopy at storage rings

Laser spectroscopy at storage rings often suffers from a limited resolution due to Doppler-broadened resonances. Broadening is caused by the velocity spread of the ions stored in the beam. In the following, the present status of our work on laser systems specialized on the specific needs of laser spectroscopy at storage rings is reported. Two pulsed laser systems were developed. One is a dye laser whose spectral bandwidth can be switched by inserting different Littrow-prisms into the resonator. An increase in bandwidth up to a factor of 45 was achieved. This laser was used for fast qualitative scans and high resolution measurements. The other laser system is a Nd : YAG laser pumped optical parametric oscillator. It is a tunable laser system covering the spectral range from 410 to 4000 nm. Furthermore, a continuous wave laser with a frequency shifted feedback cavity is described. It shows broadband emission with an adjustable bandwidth of up to 4.5 GHz. This laser can be advantageous for laser cooling of ion beams. This revised version was published online in August 2006 with corrections to the Cover Date.     

A parallel version of the preconditioned conjugate gradient method for boundary element equations

The parallel version of precondition techniques is developed for matrices arising from the Galerkin boundary element method for two-dimensional domains with Dirichlet boundary conditions. Results were obtained for implementations on a transputer network as well as on an nCUBE-2 parallel computer showing that iterative solution methods are very well suited for a MIMD computer. A comparison of numerical results for iterative and direct solution methods is presented and underlines the superiority of iterative methods for large systems.     

Detection of processed genetically modified food using CIM monolithic columns for DNA isolation

The availability of sufficient quantities of DNA of adequate quality is crucial in polymerase chain reaction (PCR)-based methods for genetically modified food detection. In this work, the suitability of anion-exchange CIM (Convective Interaction Media; BIA Separations, Ljubljana, Slovenia) monolithic columns for isolation of DNA from food was studied. Maize and its derivates corn meal and thermally pretreated corn meal were chosen as model food. Two commercially available CIM disk columns were tested: DEAE (diethylaminoethyl) and QA (quaternary amine). Preliminary separations were performed with standard solution of salmon DNA at different pH values and different NaCl concentrations in mobile phase. DEAE groups and pH 8 were chosen for further isolations of DNA from a complex matrix-food extract. The quality and quantity of isolated DNA were tested on agarose gel electrophoresis, with UV-scanning spectrophotometry, and by amplification with real-time PCR. DNA isolated in this way was of suitable quality for further PCR analyses. The described method is also applicable for DNA isolation from processed foods with decreased DNA content. Furthermore, it is more effective and less time-consuming in comparison with the existing proposed methods for isolation of DNA from plant-derived foods.     

A new high-spin isomer in 39 97 Y58

An isomeric state at 3,523 keV excitation energy in⁹⁷Y with a half-life of 144(10) ms has been discovered with the fission-product separator JOSEF. This isomer is depopulated through aγ transition of 162 keV. AnE3 multipolarity for this transition is consistent with the measured conversion coefficients ofα _K =0.98(20) andα _T =1.00(19). Subsequent electromagnetic transitions populate several new⁹⁷Y levels which have high spins. For the isomer the three-quasiparticle configuration [πg _9/2?ν(h _11/2,g _7/2)]27/2^? is proposed. TheE3 transition with a strength about 2 single-particle units is supposed to be of the typeh ₁₁ ^2/+1 →d ₅ ^2/?1 . These findings provide evidence for the rapid shape transition atA?100 since they indicate shell-model character of ₃₉ ⁹⁷ Y₅₈ even at high excitation energies while the immediate neighbour ₃₉ ⁹⁸ Y₅₉ contains a rotational band based on a level at 495 keV.     

Rapid determination of ethylene glycol at toxic levels in serum and urine

The rapid gas chromatographic detection and determination of ethylene glycol in biological fluids is described. Phenylboronic acid in acetone was used for the esterification of glycol. The phenylboronates of ethylene glycol and 1,2-propylene glycol are not separated on a packed column of medium polarity (OV-17), but they can be separated on a non-polar column (OV-101). In both instances, 1,3-propylene glycol can be used as an internal standard. The method requires only 100 microliters of serum or urine and is suitable for trace analysis in an emergency toxicological laboratory. The utility of the method is demonstrated on two cases of human intoxication with ethylene glycol.     

Thiyl radical interaction with pyrimidine C5-C6 double bond

Addition and elimination interaction of thiyl radicals with the C5-C6 double bond in pyrimidines was studied by the pulse radiolysis technique in aqueous solution with the use of different monitoring systems. For this purpose, p-thiocresol, cysteamine hydrochloride, and mercaptoethanol were used. The rate constants of addition and elimination of thiyl radicals were determined by applying the modified version of ACUCHEM (computer program for modeling complex reaction systems). Aliphatic thiyl radicals add to the pyrimidine C5-C6 double bond with k = 1.0-3.0 x 10(7) dm3 mol(-1) s(-1), whereas elimination takes place with k = 0.7-2.0 x 10(5) s(-1). Quantum chemical calculations at the B3LYP/6-31G(d)/PCM level show that the addition should occur at the C6 position of the pyrimidine ring and that the energy of interaction between thiyl radicals and the pyrimidine double bond C5-C6 is low.     

Ionization of cyclic aromatic amines by free electron transfer: products are governed by molecule flexibility

The bimolecular electron transfer from secondary aromatic amines to parent radical cations of nonpolar solvents such as alkanes and alkyl chlorides results in the synchronous formation of amine radical cations as well as aminyl radicals, in comparable amounts. If as for cyclic aromatic amines (c-Ar(2)NH) the intramolecular bending motion around the amine group is restricted in varying degrees (acridane, phenothiazine) or completely prevented (carbazole), then this picture is modified. In the free electron transfer, the completely rigid carbazole yields exclusively amine radical cations. Acridane exhibits preferred radical cations, but phenothiazine with the more flexible six-membered ring involving sulfur as a further heteroatom follows the common two-product rule; see above. The phenomenon is reasoned by a peculiarity in the bimolecular free electron transfer where after diffusional approach the actual electron jump proceeds in the ultrashort time range. Therefore, it reflects femtosecond molecular motions which, in the case of free mobility, continuously pass through different molecule conformers, combined with fluctuation of the electrons of the responsible molecular n-orbitals. The rigid systems, however, do not show this effect because of a nonexistent bending motion.     

Substituent Effects on the C-C Bond Strength, 15[1] Geminal Substituent Effects, 7[2]. Thermochemistry and Thermal Decomposition of Alkyl-substituted Tricyanomethyl Compounds

The thermolysis reactions of the tricyanomethyl compounds 10a-c were studied in solution. 2,2-Dicyano-3-methyl-3-phenylbutyronitrile ( 10a ) and 2,2-dicyano-3-methyl-3-(4-nitrophenyl)butyronitrile ( 10b ) decomposed heterolytically into carbenium ions and (CN)₃C⁻ anions, while 9-methyl-9-(tricyanomethyl)fluorene ( 10c ) underwent about 11% homolytic C-C bond cleavage into 9-methyl-9-fluorenyl- and tricyanomethyl radicals. The rates of the homolysis were determined by a radical scavenger procedure under conditions of pseudozero order kinetics. From the temperature effect on the rate constants the activation parameters were determined [ΔH ( 10c ) = 155· 2 kJ mol⁻¹, ΔS ( 10c ) = 58· 5 J mol⁻¹ K⁻¹]. Standard enthalpies of formation ΔH (g) were determined for 2,2-dicyanopropionitrile ( 2 ) (422.45 kJ mol⁻¹), 2,2-dicyanohexanenitrile ( 3 ) (349.74 kJ mol⁻¹), 2,2-dicyano-3-phenylpropionitrile ( 4 ) (540.75 kJ mol⁻¹), 2-butyl-2-methylhexanentrile ( 5 ) (-133.20 kJ mol⁻¹), 2,2-dimethylpentanenitrile ( 6 ) (-45.78 kJ mol⁻¹), and 2-methylbutyronitrile ( 7 ) (2.44 kJ mol⁻¹) from the enthalpies of combustion and enthalpies of sublimation/vaporization. From these data and known Δ (g) values for alkanenitriles and -dinitriles, thermochemical increments for ΔH (g) were derived for alkyl groups with one, two, or three cyano groups attached. The comparison of these increments with those of alkanes reveals a strong geminal destabilization, which is interpreted by dipolar repulsions between the cyano groups. - From ΔH (g) of 10c and ΔH of its homolytic decomposition the radical stabilization enthalpy for the tricyanomethyl radical 1 RSE ( 1 ) = -18 kJ mol⁻¹ was determined. Thus, 1 is destabilized, in comparison with the RSEs of tertiary α-cyanalkyl (23 kJ mol⁻¹) and α,α-dicyanoalkyl (27 kJ mol⁻¹) radicals, which were recalculated from bond homolysis measurements^[4] and the new thermochemical data. This change of RSE on increasing the number of α-cyano groups is discussed as the result of the additive contributions by resonance stabilization and increasing destabilization by dipolar repulsion. The amount of the dipolar energies was estimated by molecular mechanics (MM2).     

Study of perrhenate reduction by capillary electrophoresis

The influence of perrhenate concentration, the concentration of the reducing agent and pH of the reaction mixture on the yield of perrhenate reduction were studied to find a possibility to decrease the stannous chloride concentration in the reaction mixture without negative changes on the yield of perrhenate reduction. Britton-Robinson buffer solutions were selected as the background electrolytes because of their buffering capacity in a wide pH interval. The highest degree of perrhenate reduction was obtained at pH 2 at perrhenate concentrations ranging from 10(-4) to 10(-3) mol/L. The stability of reduced rhenium against pH change from 2 to 5.5 and against dilution of rhenium in the reaction mixture to the concentration suitable for the application in radiotherapy were studied as well. The results obtained by capillary electrophoresis and by thin-layer chromatography with radiometric detection were compared.