The Degradation of the Active Medium of an Argon Fluoride Discharge Lamp with a Noncorrosive Gas Mixture

The results of a spectroscopic study on the degradation of the active medium of an ArF electric-discharge lamp with the He–Ar–SF₆ working mixture (p 100 kPa) and pumped by a transverse space discharge are presented. Plasma radiation spectra were studied over the range 190–780 nm at different stages of degradation of the working mixture, and the dynamics of emission from the inert gases, as well as the products of sulfur hexafluoride degradation in the plasma, were determined. The ArF(B–X) emission band at = 193 nm was observed when the number of discharge pulses was 10³, whereas the quite effective formation of excited sulfur molecules, which decomposed producing emission bands in the spectral region of 260–550 nm, took place at n 10⁴.     

Operating mechanism of the electrolyte cathode atmospheric glow discharge

Cathode fall (U_cf), cathodic current density and atomic emission intensities originating from metal salts in the electrolyte cathode were measured as a function of different discharge parameters. Emission intensities in function of cathode fall indicate a potential barrier in the sputtered mass flux. This means that the primary particles of the cathode sputtering are of positive charge and the cathode fall including its internal variables is the most important factor. The measured current density and the U_cf as a function of pressure are in accordance with the low pressure data in the literature. The observed decrease of the U_cf with decreasing pH was explained by a model in that the secondary electron emission coefficient of the cathode () is controlled through a reaction net of competing reactions of different electron scavengers involving the hydroxonium ions of the cathode solution. The model revealed two different electron emission processes of the electrolyte cathode, an emission coupled with hydrated electrons is dominating below pH 2.5 while a proton-independent emission of poor efficiency is working above pH 3. Our model fits to the reported yields of the ultimate products both in the solution and in the gas phase and offers a calculation of and U_cf in the function of the cathode acidity. The model provides two other independent calculation methods based on product analysis data.     

Switchable Ambient‐Temperature Singlet–Triplet Dual Emission in Nonconjugated Donor–Acceptor Triarylboron–PtII Complexes

Double the fun! Singlet–triplet dual emission at ambient temperature has been achieved in compounds containing a triarylboron acceptor and an N‐(2′‐pyridyl)‐7‐azaindolyl donor group bridged by a tetrahedral Si linker (see figure). Pt^II chelation and chelate‐mode switching from N,N to N,C have been found to greatly enhance phosphorescent emission. Furthermore, both singlet and triplet emission bands are responsive to fluoride ions.

     

X-ray emission spectroscopy and the electronic structure of heterocyclic compounds

The electronic structure of the pyridine molecule has been investigated by x-ray emission spectroscopy. The NK _y and CK _y emission spectra have been measured. Ab initio and MNDO calculations have been carried out and individual bands in the spectra have been identified subsequently. The calculations produce spectral contours which approximate those of the experimental spectra.For Communication 3 see [1].Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 11, pp. 1484–1487, November, 1993.     

Factors affecting the formation in the solid state of the metastable complex between naphthalene and dimethyl-β-cyclodextrin

An equimolar mixture of naphthalene and amorphous heptakis-(2,6-di-O-methyl)--cyclodextrin (DMCD) was heated at 70 or 90°C in a sealed container. After heating ffor 15 min at 90°C, the mixture was crystallized to show an excimer fluorescence of naphthalene, and the fluorescence spectrum changed to a monomer emission by further prolongation of heating time, accompanied by a slight change in its powder X-ray diffractogram. It is suggested that a metastable complex showing the excimer emission of naphthalene was transformed to a stable complex showing the monomer emission. The mixing molar ratio of naphthalene to DMCD was also found to affect the transformation temperature of the complex.     

Effects of substituent and solvent on the structure and spectral properties of maleimide derivatives

The maximum absorption wavelength , emission wavelength (λ_em) and the related oscillator strength (f) of the maleimides in the ground and first excited states were calculated by using the DFT, CIS and the time-dependent density functional theory (TD-DFT) methods, where the molecular structures were optimized by DFT/B3LYP/6-31G^* calculation. Solvent effects on the maleimides were examined using the PCM simulation at DFT/B3LYP level with the 6-31G^* basis set. For N-substituted maleimide, the substituent gives only a slight influence on the maleimide chromophore, while planar conformation of PhMLH leads to the improvement in π-delocalization from substituent to maleimide unit. For 3,4-substituted maleimide, the steric repulsion between substituent and maleimide chromophore influences the extent of π-delocalization and the molecular conformation. The calculated and λ_em of maleimides are in good agreement with the experimental data. In the gas phase, both absorption and emission peaks are red-shift as compared to the non-substituted maleimide. Under solvent environment, the more planar conformation of PhMLH shows a blue-shift in the calculated and λ_em as compared with other N-substituted maleimides. For 3,4-substituted maleimides, the effect of substitution produces the most significant spectral red-shift as compared to other maleimides.     

Bioluminescence resonance energy transfer from aequorin to a fluorophore: an artificial jellyfish for applications in multianalyte detection

In nature, the green light emission observed in the jellyfish Aequorea victoria is a result of a non-radiative energy transfer from the excited-state aequorin to the green fluorescent protein. In this work, we have modified the photoprotein aequorin by attaching selected fluorophores at a unique site on the protein. This will allow for in vitro transfer of bioluminescent energy from aequorin to the fluorophore thus creating an artificial jellyfish. The fluorophores are selected such that the excitation spectrum of the fluorophore overlaps with the emission spectrum of aequorin. By modifying aequorin with different fluorophores, bioluminescent labels with different emission maxima are produced, which will allow for the simultaneous detection of multiple analytes. By examining the X-ray crystal structure of the protein, four different sites for introduction of the unique cysteine residue were evaluated. Two fluorophores with differing emission maxima were attached individually to the mutants through the sulfhydryl group of the cysteine molecule. Two of the fluorophore-labeled mutants showed a peak corresponding to fluorophore emission thus indicating resonance energy transfer from aequorin to the fluorophore.     

Radial distribution measurement of SiH* in a low-pressure silane plasma

The radial emission intensity distribution of SiH^* (A²,v=0) over the substrate of a low-pressure silane plasma was investigated for various substrate temperatures (T _s=20–320°C). Measured lateral intensities were converted to radial emission coefficients using an Abel inversion. The intensity near the center of the substrate was found to increase withT _s and yielded an activation energyE _a of 1.1 kcal/mole. This result is consistent with the value ofE _a determined by laser-induced flourescence measurements obtained previously. Radially resolved emission data obtained by varying the operating parameters of rf power, gas flow rate, silane/argon mixing rate, and total gas pressure provide a useful means of determining the conditions necessary to generate a uniform plasma.     

The Photophysical Properties of Ruthenium Polypyridyl Complexes within a Sol-Gel Matrix

Tetraethoxysilane (TEOS) sol-gel monoliths impregnated with three different luminescent [Ru(L)₃]²⁺ complexes (where L = 2,2-bipyridine (bpy), 1,10-phenanthroline (phen), or 4,7-diphenyl,1,10-phenanthroline (dpp)) have been prepared. The photoluminescence properties of these complexes were followed as a function of time, as the sol-gel reactions proceeded. Clear differences were observed in the emission energies and the emission lifetimes of the complexes upon gel formation. These differences can be explained by the different extent of electrostatic interaction between the surface of the siloxane polymer and the immobilised complex.     

Simultaneous Determination of the Concentration of Elements and Their Speciation in Solid Samples Using X-ray Fluorescence Spectrometry

A method is proposed for the X-ray emission analysis of solid samples in which two analytical signals are used in one experiment. The first signal depends on the structure and type of the chemical compound in the test sample, and the second one is used for determining the concentration of elements entering into the composition of the test sample. The relative integral intensity of the last emission line in the characteristic X-ray spectrum is used as the first analytical signal. This line is due to an electron transition from the valence band to an inner atomic level (for example, the K ₂ line for elements from Cu to Br). The spectral intensity of the brightest (K , L and, less frequently, M or M ) lines of the characteristic X-ray spectrum serves as the second analytical signal, which is conventionally used in X-ray fluorescence analysis.     

New π‐Conjugated Polymers Containing 1,3,5‐Triazine Units in the Main Chain: Synthesis and Optical and Electrochemical Properties of the Polymers

Summary: Three new soluble π‐conjugated polymers containing 1,3,5‐triazine units in the main chain, Pa–Pc, were synthesized. The polymers showed optical properties in solution that were mainly dependant on the properties of the substituting R groups, on the triazine ring. Hence, Pa and Pb (R = H and  OCH₃, respectively) showed blue photoluminescent (PL) emission with high quantum yields (QY) even in polar solvents, whereas Pc (R = N,N‐dimethylamino) gave green‐blue PL emission with very low QY. The PL spectra of the polymers in solution were concentration and polarity dependent, which suggested the formation of an exciplex.

The three new soluble π‐conjugated polymers containing 1,3,5‐triazine units in the main chain synthesized here.     

A new cataluminescence sensor for carbon tetrachloride using its catalytic reduction by hydrogen on palladium/carbon surface

A new cataluminescence (CTL) sensor was developed based on the chemiluminescence (CL) emission from the catalytic hydrodechlorination of carbon tetrachloride on the surface of palladium/carbon catalyst. The factors influencing the CTL signal, such as the catalyst, carrier gas, gas flow rate, temperature and the CL wavelength, were investigated in detail. Under the optimal conditions, the linear range of the CTL intensity versus concentration of carbon tetrachloride was 4.7–235 μg/mL (R = 0.9944, n = 7), with a limit of detection of 0.7 μg/mL (σ = 3). GC/MS results suggest that the possible CTL mechanism of the reduction is the formation of CCl₃ radicals. The CCl₃ radicals combine with H free atoms or capture hydrogen atoms from H₂ molecules to form excited CHCl₃ intermediates, which decay from the excited-state to the ground giving CTL emission for the detection. It is also found that some benzene derivatives with α-H of branched-chain, such as toluene, ethylbenzene and xylenecan, can play a role of catalyst in the reaction.     

Secondary ion emission of selected transition metals under nitrogen oxides

The emission of various positive secondary ions has been investigated for polycrystalline targets of Ti, V, Cr, Nb, Ta, Co, Ni, Cu, Pd and Pt, which were bombarded by Ar⁺ ions under dynamic SIMS (DSIMS) conditions in the presence of the gaseous nitrogen oxides N₂O, NO and NO₂ at fixed pressure and under residual gas. Besides ions of the Me⁺ type several fragmentary ions (e.g. N⁺, O⁺, NO⁺, MeN⁺ and MeO⁺) and also cluster ions Me _x O _y ⁺ (x 2, 0 y 2) were detected. Signals of a more molecular type with respect to the reactant gas, e.g. MeNO⁺, were only found for Co, Ni, Cu, Pd and Pt. From this, one may infer that for the other targets the nitrogen oxides will exist preferentially in a dissociatively adsorbed state at the metal surface. Several aspects of secondary ion emission can be explained assuming a different degree of oxidation for the metals under the influence of reactant gas.Part of the dissertation     

Highly Efficient and Well‐Controlled Ambient Temperature RAFT Polymerization under Solar Radiation

Highly efficient and well‐controlled ambient temperature reversible addition–fragmentation chain transfer (RAFT) polymerization is readily carried out under environmentally friendly mild solar radiation. This discovery has significantly extended studies from man‐made separated‐spectroscopic‐emission UV‐vis radiation (Macromolecules 2006 , 39, 3770) to natural continuous‐spectroscopic‐emission solar radiation for ambient temperature RAFT polymerization.

     

Kinetic Study of the Chemiluminescence Spectrum of Rarified Flame in Dichlorosilane Oxidation in the Near IR Region

Electronically excited HO ₂ ^. radicals (A ² A"–X ² A"), OH^.radicals (= 2 – 0), and HCl molecules (= 3 – 0) are identified using the emission spectra at 0.8–1.6 m in the rarefied flame in dichlorosilane combustion at 293 K and low pressures. The spectrum also contains the composite bands of the H₂O (0.823 m) and H₂O₂(0.854 m) molecule vibrations. The maximum intensity of emission of these species is attained behind the front of the active chemical transformation, and the equilibrium between the vibrational and translational degrees of freedom is established in the region of the regular thermal regime of cooling. SF₆additives act as a reservoir that accumulates the vibrational energy in developed ignition. The processes responsible for the inhibition of dichlorosilane oxidation by SF₆additives are considered.     

On the measurement of infrared emission spectra using grating spectrometers

Summary The practical limits for IR emission measurements with conventional grating spectrometers have been checked using thin solid films on metal substrates as samples. Favourable conditions provided (large sample area, appropriate sample thickness), good quality emission spectra, which are in excellent agreement with corresponding absorption spectra, can be obtained without too much experimental requirements (temperatures below 100° C, no special optics) and within a reasonable time (less than 1 h). Because of the restricted instrument sensitivity, however, lower limits for the experimental parameters (temperature, sample area, thickness) rapidly are reached, below which the recorded emission spectra become useless. These limits are about 40° C for the sample temperature, 0.5 cm² for the sample area and 1m for the thickness of a polystyrene sample. For the sample thickness there exists an upper limit too, since with increasing thickness the emissivity converges to (1-reflectivity) within the whole frequency range, similar to absorption spectra, which converge to zero transmission. The upper limits for the permissible thicknesses are very similar for emission and absorption, being about 100m for polystyrene.Dedicated to Prof. K. Schlögl for his 60th birthday.     

Remarkable Change in Fluorescence Emission of Poly(diphenylacetylene) Film via in situ Desilylation Reaction: Correlation with Variations in Microporous Structure,Chain Conformation,and Lamellar Layer Distance

Fluorescence (FL) emission properties, microporous structures, energy‐minimized chain conformations, and lamellar layer structures of the silicon‐containing poly(diphenylacetylene) derivative of p‐PTMSDPA before and after desilylation were investigated. The nitrogen‐adsorption isotherms of p‐PTMSDPA film before and after desilylation were typical of type I, indicating microporous structures. The BET surface area and pore volume of the p‐PTMSDPA film were significantly reduced after the desilylation reaction, simultaneously, its FL emission intensity remarkably decreased. The theoretical calculation on both model compounds of p‐PTMSDPA and its desilylated polymer, PDPA, showed a remarkable difference in chain conformation: The side phenyl rings of p‐PTMSDPA are discontinuously arranged in a zig‐zag pattern, while the PDPA is continuously coiled in a helical manner. The lamellar layer distance (LLD) in the p‐PTMSDPA film significantly decreased after the desilylation reaction.

     

Untersuchungen an Röntgenemissionsprofilen von leichten Elementen mit der „Makrosonde”

Zusammenfassung Die Verschiebungen der Lage der Intensitätsmaxima im Röntgenemissionsprofil eines Elementes in verschiedenen Verbindungen werden mit chemischen Parametern in Zusammenhang gebracht, indem die Röntgenemissionsprofile von Sauerstoff in einer Reihe von Oxiden mit der Makrosonde aufgenommen und die Verschiebungen des Intensitätsmaximums im Sauerstoffemissionsprofil ermittelt werden. Dabei zeigt sich, daß die sogenannte Linienverschiebung von Sauerstoff in einem direkten stetigen Zusammenhang mit der Standardbildungsenthalpie der Oxide steht. Bei dem VerbindungstypMe₂O₃ zeigt sich außerdem eine annähernd lineare Abhängigkeit der Energie des Intensitätsmaximums im Sauerstoffemissionsprofil vom Ionencharakter der Metall-Sauerstoffbindung.Die Auswertung der Linienverschiebungen von Kohlenstoff, Stickstoff, Fluor und Chlor nach Literaturdaten zeigt, daß bei allen diesen Systemen ebenfalls ein stetiger Zusammenhang zwischen Linienverschiebung und Bildungsenthalpie besteht. Bei einigen Systemen—wie bei denen von Kohlenstoff und Chlor-besteht auch ein direkter Zusammenhang zwischen der Energie des Intensitätsmaximums im Emissionsprofil und dem Ionencharakter der Metall-Nichtmetallbindung.

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Studies of the X-ray emission profiles of light elements with the primary X-ray analyzer

The shifts of the position of the intensity maxima in the X-ray emission profile of an element in different compounds are correlated with chemical parameters by recording the X-ray emission profiles of oxygen in a series of oxides with the makrosonde and determining the shifts of the intensity maximum in the oxygen emission profile. It can thus be shown that between the so-called line shift of oxygen and the standard enthalpies of formation of the oxides a direct and continuous relationship exists. In compounds of the typeMe ₂O₃ there is in addition an almost linear dependence of the energy of the intensity maximum in the oxygen emission profile from the ionic character of the metal-oxygen bond.Interpretation of the line shifts of carbon, nitrogen, fluorine and chlorine according to literature data shows that in all these systems a continuous relationship between line displacement and enthalpy of formation likewise exists. In a few systems-such as those of carbon and chlorine-there is furthermore a direct relationship between the energy of the intensity maximum in the emission profile and the ionic character of the metal-nonmetal bond.

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Mit 11 Abbildungen

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Herrn Prof. Dr.H. Nowotny gewidmet.     

Some aspects of the interactions of orthopositronium with perfect and defect surfaces of insulating materials

ETLA (Elastic Thermalisation Lifetime Analysis) is a new model function for the fitting of lifetime spectra of slowly thermalising orthopositronium in the free space between the grains of insulating oxide powders. From this model one can obtain three fundamental parameters; the mass of the cluster of atoms which scatters the o-Ps, the probability that the o-Ps is forced into two-quantum decay at each collision and the emission energyE(0) of the o-Ps from the powder surface. As a consequence of full thermalisation of the Ps it is shown that the o-Ps quenching constant _q () follows atT ^1/2 dependency for MgO, Al₂O₃ and SiO₂ and for temperatures between 77 and 500 K. In MgO powder at low temperatures the irradiation by the positrons induces surface paramagnetic defects which are identified as Mg⁺ sites. These surface defects do not affect the thermalisation, but they induce paramagnetic o-p conversion i.e., an increase in , and they are also responsible for an increase in the emission energyE(0) of the o-Ps.