The dushinsky effect in resonance Raman spectroscopy

The effect of normal-coordinate rotation on resonance Raman excitation profiles and depolarization dispersion curves is investigated theoretically for two nontotally symmetric modes of the same symmetry.     

Flow injection potentiometry for low level measurements in the presence of sensed ion in the carrier

Summary A theoretical treatment of the response of ion sensitive electrodes in flow-injection analysis is presented with emphasis on the influence of sample dispersion and the addition of sensed ion to the carrier solution. Guidelines are given for optimal conditions with respect to desired working range and sensitivity, i.e., the slope of the calibration plot. The comparison of predicted data and experimental results obtained with the fluoride and iodide sensitive electrodes showed significant deviations due to slow response. For low dispersion systems (D _max 1) a method for linearization of the calibration plot is proposed.

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Fließinjektions-Potentiometrie für Messungen niedriger Konzentrationen in Gegenwart des zu messenden Ions in der Trägerlösung

     

Using mixture density functions for modelling of wage distributions

This article explores the possibility of modeling the wage distribution using a mixture of density functions. We deal with this issue for a long time and we build on our earlier work. Classical models use the probability distribution such as normal, lognormal, Pareto, etc., but the results are not very good in the last years. Changing the parameters of a probability density over time has led to a degradation of such models and it was necessary to choose a different probability distribution. We were using the idea of mixtures of distributions (instead of using one classical density) in previous articles. We tried using a mixture of probability distributions (normal, lognormal and a mixture of Johnson’s distribution densities) in our models. The achieved results were very good. We used data from Czech Statistical Office covering the wages of the last 18 years in Czech Republic.     

Wavepacket of the Universe and its Spreading

Wavepackets in quantum mechanics spread and the Universe in cosmology expands. We discuss a formalism where the two effects can be unified. The basic assumption is that the Universe is determined by a unitarily evolving wavepacket defined on space-time. Space-time is static but the Universe is dynamic. Spreading analogous to expansion known from observational cosmology is obtained if one regards time evolution as a dynamical process determined by a variational principle employing Kolmogorov-Nagumo-Rényi averages. The formalism automatically leads to two types of “time” parameters: τ, with dimension of x⁰, and dimensionless ε = ln??_τ, related to the form of diffeomorphism that defines the dynamics. There is no preferred time foliation, but effectively the dynamics leads to asymptotic concentration of the Universe on spacelike surfaces which propagate in space-time. The analysis is performed explicitly in 1 + 1 dimensions, but the unitary evolution operator is brought to a form that makes generalizations to other dimensions and other fields quite natural.     

Identification of conical structures in small aluminum oxide clusters: infrared spectroscopy of (Al2O3)1-4(AlO)+

The vibrational spectroscopy of the electronically closed-shell (Al 2O 3) n (AlO) (+) cations with n = 1-4 is studied in the 530-1200 cm (-1) range by infrared predissociation spectroscopy of the corresponding ion-He atom complexes in combination with quantum chemical calculations. In all cases we find, assisted by a genetic algorithm, global minimum structures that differ considerably from those derived from known modifications of bulk alumina. The n = 1 and n = 4 clusters exhibit an exceptionally stable conical structure of C 3 v symmetry, whereas for n = 2 and n = 3, multiple isomers of lower symmetry and similar energy may contribute to the recorded spectra. A blue shift of the highest energy absorption band is observed with increasing cluster size and attributed to a shortening of Al-O bonds in the larger clusters. This intense band is assigned to vibrational modes localized on the rim of the conical structures for n = 1 and n = 4 and may aid in identifying similar, highly symmetric structures in larger ions.     

Covalent bonding of azoles to quaternary protoberberine alkaloids

Adducts of the quaternary protoberberine alkaloids (QPA) berberine, palmatine, and coptisine were prepared with nucleophiles derived from pyrrole, pyrazole, imidazole, and 1,2,4-triazole. The products, 8-substituted 7,8-dihydroprotoberberines, were identified by mass spectrometry and 1D and 2D NMR spectroscopy, including (1)H--(15)N shift correlations at natural abundance. In addition, two adducts of QPA with chloroform and methanethiolate were characterized by using NMR data. Single-crystal X-ray structures of 8-pyrrolyl-7,8-dihydroberberine, 8-pyrazolyl-7,8-dihydroberberine, and 8-imidazolyl-7,8-dihydroberberine are also presented.     

Kinetics and mechanism of sensitized photooxidation of tetramethylammonium salt of 2-(phenylthio)acetic acid in solution: Steady-state and flash photolysis studies

The mechanism for the photo-induced oxidation of the tetramethylammonium salt of 2-(phenylthio)acetic acid was elucidated. The photosensitizer was the benzophenone triplet in acetonitrile solutions. Time-resolved absorption spectra and kinetics were used to follow the intermediates which included the triplet of benzophenone, the ketyl radical of benzophenone, and an ion pair consisting of a radical anion of benzophenone and a tetramethylammonium cation. Rate constants for the growth and decay of the transients were determined along with the quantum yields of the transients. The intermediacy of other radicals was inferred by the products observed following steady-state photolysis. Quantum yields were also determined for photoproducts resulting from the steady-state irradiation. The mechanism was proposed that rationalized the quantitative observations. Of particular note was how the nature of the counter ion effected the secondary reactions of the radicals and the radical ions.     

Spectroscopy and photophysics of 1,4-bis(phenylethynyl)benzene: effects of ring torsion and dark pi sigma* state

A combination of supersonic-jet laser spectroscopy and quantum chemistry calculation was applied to 1,4-bis(phenylethynyl)benzene, BPEB, to study the role of the dark pisigma* state on electronic relaxation and the effect of ring torsion on electronic spectra. The result provides evidence for fluorescence break-off in supersonic jet at high S1(pi pi*) <-- S0 excitation energies, which can be attributed to the pi pi*-pi sigma* intersection. The threshold energy for the fluorescence break-off is much larger in BPEB (approximately 4000 cm(-1)) than in diphenylacetylene (approximately 500 cm(-1)). The high-energy barrier in BPEB accounts for the very large fluorescence quantum yield of the compound (in solution) relative to diphenylacetylene. The comparison between the experimentally derived torsional barrier and frequency with those from the computation shows overall good agreement and demonstrates that the low-energy torsional motion involves the twisting of the end ring in BPEB. The torsional barrier is almost an order of magnitude greater in the pi pi* excited state than in the ground state. The finding that the twisting of the end ring in BPEB is relatively free in the ground state, but strongly hindered in the excited state, provides rationale for the well-known temperature dependence of the spectral shape of absorption and the lack of mirror symmetry relationship between the absorption and fluorescence at elevated temperatures.     

A selective convenient ruthenium-mediated synthesis of mixed acetals

Addition of alcohols and phenols to allyl ethers catalyzed mainly by ruthenium complexes was studied. Complexes of ruthenium generated in situ from precursors such as {[RuCl₂(1,5-COD)]_x} or [Ru₃(CO)₁₂] and from external ligands such as phosphines (e.g. PPh₃, PBu₃, BINAP) or phosphites (e.g. P(OPh)₃, P(OMe)₃) were found to be particularly efficient catalysts of the studied reactions. Transacetalization reaction could be practically completely eliminated by the addition of a base (particularly Na₂CO₃) to the catalytic systems. It was observed that the selectivity of mixed acetals formation increases with increasing value of Θ parameter of phosphines. Especially interesting results (0–5% of transacetalization) have been obtained for catalytic systems generated from {[RuCl₂(1,5-COD)]_x} or [Ru₃(CO)₁₂], phosphines (PPh₃, BINAP, dppe, tris(2,4,6-tri-metylphenyl)phosphine, or dppf) and Na₂CO₃. The mechanism of mixed acetals formation has been investigated using deuterated reagents. It is postulated that the examined reaction is a nucleophilic addition of ROH to a hydrido-π-allyl complex formed during oxidative addition of allyl substrate to metal complex. As a result, a new, selective, and convenient method of the synthesis of symmetrical and, in particular, unsymmetrical (mixed) acetals has been developed. Mixed acetals CH₃CH₂CH(OR¹)(OR²) may be obtained in the reaction of R¹-O-allyl with R²OH or R¹OH with R²-O-allyl, depending on the structure of R¹ and R².