Stark- and Zeeman-effect of resonance lines of Ba I

Laserspectroscopic investigations were performed on a collimated atomic beam of barium (natural isotope abundance). The metastable ground levels (³D_1,2,3 and ¹D₂) of the investigated lines were populated by a discharge burning in barium vapour directly in front of the oven hole. We could investigate 14 spectral lines between 580 and 690 nm. The tensor polarizabilities of the upper and the lower level as well as the differences in the scalar polarizabilities could be determined. Spectra in magnetic fields up to 0.03 Tesla showed no deviation from the pattern resulting from a simple Russell-Sounders coupling.     

Infrared absorption by collisional CH4+X pairs, with X=He, H2, or N2

Existing measurements of the collision-induced rototranslational absorption spectra of gaseous mixtures of methane with helium, hydrogen, or nitrogen are compared to theoretical calculations, based on refined multipole-induced and dispersion force-induced dipole moments of the interacting molecular pairs CH4-He, CH4-H2, and CH4-N2. In each case the measured absorption exceeds the calculations substantially at most frequencies. We present the excess absorption spectra, that is the difference of the measured and the calculated profiles, of these supramolecular CH4-X systems at various gas temperatures. The excess absorption spectra of CH4-X pairs differ significantly for each choice of the collision partner X, but show common features (spectral intensities and shape) at frequencies from roughly 200 to 500 cm(-1). These excess spectra seem to defy modeling in terms of ad hoc exchange force-induced dipole components attempted earlier. We suggest that besides the dipole components induced by polarization in the electric molecular multipole fields and their gradients, and by exchange and dispersion forces, other dipole induction mechanisms exist in CH4-X complexes that presumably are related to collisional distortion of the CH4 molecular frame.     

Near infrared reflectance spectroscopy for the fast identification of PVC-based films

Near infrared (NIR) reflectance spectroscopy was used to develop a non-destructive and rapid qualitative method for the analysis of plastic films used by the pharmaceutical industry for blistering. Three types of films were investigated: 250 microm PVC [poly(vinyl chloride)] films, 250 microm PVC films coated with 40 g m(-2) of PVDC [poly(vinylidene dichloride)] and 250 microm PVC films coated with 5 g m(-2) of TE (Thermoelast) and 90 g m(-2) of PVDC. Three analyses were carried out using different pre-treatment options and a PLS (partial least squares) algorithm. Each analysis was aimed at identifying one type of film and rejecting all types of false sample (different thickness, colour or layer). True and false samples from four plastics manufacturers were included in the calibration sets in order to obtain robust methods that were suitable regardless of the supplier. Specificity was demonstrated by testing validation sets against the methods. The tests showed 0% of type I (false negative identification) and 1% of type II errors (false positive identification) for the PVC method, 13 and 3%, respectively, for the PVC-PVDC method and no error for the PVC-TE-PVDC method. Type II errors, mostly due to the slight sensitivity of the methods to film thickness, are easily corrected by simple thickness measurements. This study demonstrates that NIR spectroscopy is an excellent tool for the identification of PVC-based films. The three methods can be used by the pharmaceutical industry or plastics manufacturers for the quality control of films used in blister packaging.     

Instrumental neutron activation analysis of Elbe river suspended particulate matter separated according to the settling velocities

Suspended particulate matter in Elbe river water near Hamburg has been separated into different fractions by pouring the samples into special sedimentation tubes called Atterberg cylinders. The fractions are obtained by decanting the water after different settling periods, and by filtrating the decanted part. The analysis is done by neutron activation in the absolute mode, after irradiation periods of 5 min and 3 days. Mean settling velocities of the SPM-mass and the elements determined have been calculated.     

The weakly bound He-HCCCN complex: high-resolution microwave spectra and intermolecular potential-energy surface

Rotational spectra of the weakly bound He-HCCCN and He-DCCCN van der Waals complexes were observed using a pulsed-nozzle Fourier-transform microwave spectrometer in the 7-26-GHz frequency region. Nuclear quadrupole hyperfine structures due to the 14N and D nuclei (both with nuclear-spin quantum number I = 1) were resolved and assigned. Both strong a and weaker b-type transitions were observed and the assigned transitions were used to fit the parameters of a distortable asymmetric rotor model. The dimers are floppy, near T-shaped complexes. Three intermolecular potential-energy surfaces were calculated using the coupled-cluster method with single and double excitations and noniterative inclusion of triple excitations. Bound-state rotational energy levels supported by these surfaces were determined. The quality of the potential-energy surfaces was assessed by comparing the experimental and calculated transition frequencies and also the corresponding spectroscopic parameters. Simple scaling of the surfaces improved both the transition frequencies and spectroscopic constants. Five other recently reported surfaces [O. Akin-Ojo, R. Bukowski, and K. Szalewicz, J. Chem. Phys. 119, 8379 (2003)], calculated using a variety of methods, and their agreement with spectroscopic properties of He-HCCCN are discussed.     

Branched Star-Type Polysilyllithium Compounds: The Effects of beta-Silyl Substitution and of Complexation on Their Molecular Structure

No Abstract     

Investigation of an enantioselective non-aqueous capillary electrochromatography system applied to the separation of chiral acids

A weak anion-exchange type chiral stationary phase (CSP) based on tert.-butylcarbamoylquinine as chiral selector and silica as chromatographic support was applied to non-aqueous capillary electrochromatography. The mobile phases used consisted of acetonitrile and methanol as organic solvents, and acetic acid and triethylamine were added as background electrolytes. The influence of several experimental parameters (electrolyte concentration, acetic acid-triethylamine ratio, acetonitrile-methanol ratio and temperature) was evaluated in order to obtain improved enantioselectivity and efficiency as well as short run times for the enantiomeric separation of negatively charged chiral analytes including benzyloxycarbonyl, N-(3,5-dinitrobenzyloxycarbonyl, 9-fluorenylmethoxycarbonyl, benzoyl, acetyl and N-(2,4-dinitrophenyl) derivatized amino acids and profens. Solvent composition of acetonitrile-methanol (80:20) and enhanced electrolyte concentrations up to 600 mM acetic acid at a constant acid-base ratio of 100:1 with high applied voltages of -25 kV proved to be optimum regarding short retention times and improved efficiencies. For example, the enantiomers of Fmoc-Leu could be separated in less than 10 min with a resolution factor of 6.9 and about 100000 theoretical plates per meter.     

Preparatory investigations of fast separation for heavy ion reaction products

A method for separation and chemical identification of products formed in nuclear reactions or nuclear decay is to slow down the recoil products in a gas and to transport them to a trap, where a detecting system is arranged. The sources for the recoil products are²⁵²Cf and²²⁴Ra. As transport phase we used nitrogen or argon and added chemical reagents such as methyl and ethyl radicals, chlorine, oxygen, carbon monoxide or methane. The chemical additives lead to selective and fast separation of certain elements. As examples the results of two experiments are presented:²²⁴Ra with ethyl radicals, and²⁵²Cf with chlorine-oxygen-nitrogen mixtures. The registration of the recoil products at the trap was measured as a function of temperature, pressure and composition of the reactive gas.     

Examination of the swelling of heat protective hydrocolloids by DSC

While the basic fermented (sour) milk products, such as yogurt and kefir can be produced only in live flora version, the post heat-treatment is preferred in their flavored variations to increase the storage time. Casein being in sour coagulum precipitates during heat-treatment; therefore protective colloids surrounding the protein should be used to prevent it. Protective colloids are plant extracts, the most known of them are pectin and amylopectin. Basic requirement of protective colloid effect is the lower swelling temperature of hydrocolloid than the temperature of precipitation of sour coagulum. In this work we have examined the precipitation of sour coagulum as a function of the type of lactic acid bacteria cultures applied during fermentation as well as the swelling of heat protective plant hydrocolloids as a function of the composition (mainly of sugar content) of medium. To investigate the precipitation of fermented coagulum skimmed milk was fermented with mesophilic butter culture, thermophilic yogurt culture as well as with exopolysaccharide (EPS)-producing Prebiolact-2 culture. Precipitation was indicated in the increase of great extent of viscosity. Amylopectin was dispersed into aqueous solution of pH 4.5, the saccharose concentration of which was changed during the investigation of the swelling of heat protective hydrocolloids. A definite exothermic peak was assigned to the swelling of hydrocolloids during the DSC experiments. We could conclude that the precipitation temperature was increasing in the mesophilic-thermophilic-EPS producing microbes line, i.e. the heat stability and swelling temperature of hydrocolloids depend on the saccharose content of aqueous medium and they increase with rising the concentration of saccharose.