Radiative lifetime determination for the 3s4p-1P1 state of magnesium using pulsed level-crossing spectroscopy

The natural radiative lifetime of the 3s4p ¹ P ₁ level of neutral magnesium was measured by pulsed level-crossing spectroscopy at the short excitation wavelength of 202.6 nm. We obtained =13.4(5) ns for this state, strongly deviating from a previous beam-foil result, but in good agreement with a multi-configuration Hartree-Fock calculation. A discussion of the applicability of the pulsed Hanle effect method is given.     

Thio-claisen rearrangements of some ketene derivatives

A number of 1-allylthio and 1-crotylthio 1-aminoalkenes derived from ketones and active methylene compounds has been prepared and rearranged to the corresponding thioamides (thio-Claisen rearrangement). Besides rearrangement products, small amounts of 1-alkyl-thio-N-alkyl-N-phenyl-1-aminoalkenes have also been isolated. When the ketene derivatives did possess a H-atom on nitrogen, cleavage of the formed thioamide produced phenyl isothiocyanate and substituted active methylene compounds.     

Oscillator strengths for resonance transitions in neutral selenium and tellurium derived from time-resolved laser spectroscopy

We have measured radiative lifetimes for selenium and tellurium resonance levels by using short pulse laser excitation in differentially heated resonance cells. We obtained τ(³ S ₁ Se I)=2.9(5) ns and τ(³ S ₁ Te I)=3.1(5) ns, which together with branching ratio values given by Ubelis and Berzinsh yield the absorption oscillator strengthf _abs(Se I, 196.0 nm)=0.074(16) andf _abs(Te I, 214.3 nm)=0.098(17).     

Gas chromatographic determination of (phosphorylated) 2-keto-3-deoxyoctonic acid, heptoses and glucosamine in bacterial lipopolysaccharides after treatment with hydrofluoric acid, methanolysis and trifluoroacetylation

Quantification of phosphorylated sugar constituents of lipopolysaccharides has been performed by the following sequence: dephosphorylation by treatment with hydrofluoric acid, cleavage to monomeric constituents by methanolysis and analysis of the released sugars by capillary gas chromatography. Lipopolysaccharides of Salmonella minnesota Rd1P+, Bordetella pertussis NIH 114 and Vibrio cholerae, NAG and 95R strains, were used as model substances. Comparison of the chromatographic data obtained from hydrofluoric acid-treated and untreated lipopolysaccharide preparations indicated that all lipopolysaccharides examined contained one moiety of glucosamine bound to phosphate in a stable linkage. 2-Keto-3-deoxyoctonic acid appeared phosphorylated to a variable extent. Lipopolysaccharides of the two V. cholerae strains contained one moiety of fully phosphorylated 2-keto-3-deoxyoctonic acid, whereas in that of S. minnesota Rd1P+ only one of the three moieties was phosphorylated. Lipopolysaccharide of B. pertussis had one moiety of 2-keto-3-deoxyoctonic acid, ca. 70% phosphorylated. All four of the preparations examined contained L-glycero-D-manno-heptose in amounts varying from 2.6 to 5.2 moieties. In the lipopolysaccharides of B. pertussis and strain 95R of V. cholerae this sugar was unphosphorylated, whereas the two remaining strains contained one phosphorylated moiety of this sugar. Phosphorylated lipopolysaccharide constituents can be analysed by this approach on a 50-100 micrograms scale.     

Landé g J factor measurements in the 6snd 1,3 D 2 sequences of Yb I

The Landé g _J factors in the 6snd ^1,3 D ₂ sequences as well as states from the perturbing configurations of neutral Ytterbium have been measured by timeresolved fluorescence spectroscopy. Strong singlet-triplet mixing effects were observed. The g _J factors were measured using the Zeeman quantum-beat technique following step-wise laser excitation. The experiment provided new data for checking the Multi-channel Quantum Defect Theory (MQDT) used in energy-level and lifetime analysis.     

Preparative high-performance liquid chromatography of peptides on a new reversed-phase packing material, Kromasil C18

Preparative reversed-phase high-performance liquid chromatography has found wide use in the production of peptides for pharmaceutical formulations. Purity of the substance and overall economy of the chromatographic system are the most important criterias. In this sense optimized, silica particles and production process with capability to separately control parameters important to chromatography, are essential to high-performance chromatography. Kromasil C18 packing material was tested and evaluated in respect of its selectivity, flow and pressure properties, resolution, load capacity, recovery, adsorption effects, mechanical strength and chemical degradation.     

Photoionization dynamics of glycine adsorbed on a silicon cluster: "on-the-fly" simulations

Dynamics of glycine chemisorbed on the surface of a silicon cluster is studied for a process that involves single-photon ionization, followed by recombination with the electron after a selected time delay. The process is studied by "on-the-fly" molecular dynamics simulations, using the semiempirical parametric method number 3 (PM3) potential energy surface. The system is taken to be in the ground state prior to photoionization, and time delays from 5 to 50 fs before the recombination are considered. The time evolution is computed over 10 ps. The main findings are (1) the positive charge after ionization is initially mostly distributed on the silicon cluster. (2) After ionization the major structural changes are on the silicon cluster. These include Si-Si bond breaking and formation and hydrogen transfer between different silicon atoms. (3) The transient ionization event gives rise to dynamical behavior that depends sensitively on the ion state lifetime. Subsequent to 45 fs evolution in the charged state, the glycine molecule starts to rotate on the silicon cluster. Implications of the results to various processes that are induced by transient transition to a charged state are discussed. These include inelastic tunneling in molecular devices, photochemistry on conducting surfaces, and electron-molecule scattering.     

Vibrationally resolved rate coefficients and branching fractions in the dissociative recombination of O2+

We have studied the dissociative recombination of the first three vibrational levels of O(2) (+) in its electronic ground X (2)Pi(g) state. Absolute rate coefficients, cross sections, quantum yields and branching fractions have been determined in a merged-beam experiment in the heavy-ion storage ring, CRYRING, employing fragment imaging for the reaction dynamics. We present the absolute total rate coefficients as function of collision energies up to 0.4 eV for five different vibrational populations of the ion beam, as well as the partial (vibrationally resolved) rate coefficients and the branching fractions near 0 eV collision energy for the vibrational levels v=0, 1, and 2. The vibrational populations used were produced in a modified electron impact ion source, which has been calibrated using Cs-O(2)(+) dissociative charge transfer reactions. The measurements indicate that at low collision energies, the total rate coefficient is weakly dependent on the vibrational excitation. The calculated thermal rate coefficient at 300 K decreases upon vibrational excitation. The partial rate coefficients as well as the partial branching fractions are found to be strongly dependent on the vibrational level. The partial rate coefficient is the fastest for v=0 and goes down by a factor of two or more for v=1 and 2. The O((1)S) quantum yield, linked to the green airglow, increases strongly upon increasing vibrational level. The effects of the dissociative recombination reactions and super elastic collisions on the vibrational populations are discussed.     

Fluorescence of tryptophan-containing peptides on paper or silica gel after treatment with formaldehyde, formaldehyde-ozone or formaldehyde-hydrochloric acid.

Sensitive and specific procedures for the chromatographic detection of tryptophan and tryptophan-containing peptides are described. Formaldehyde gas induces strong and characteristic fluorescence from tryptophan and peptides with NH2-terminal tryptophan residues on silica gel. On filter-paper, the detection of small amounts of these compounds requires the additional use of an oxidant, such as ozone. Treatment with formaldehyde-hydrochloric acid was used as a method for inducing fluorescence from tryptophan-containing peptides regardless of the position of the tryptophan residue in the peptide molecule. This reaction is useful for the chromatographic demonstration of small amounts of such peptides on both paper and silica gel. The spectral properties of the fluorophores of such tryptophan-containing peptides are distinctive and serve to distinguish them from all other known biogenic compounds that are capable of giving fluorescence with formaldehyde.