Kinetic Study of the Emission of the First Negative System in an Argon-Nitrogen Plasma at Atmospheric Pressure

Quantitative optical spectroscopy measurements of the emission spectra of the N(B²∑_u,)ν′→X²∑_gν″ transition (first negative system) in an Ar-N₂ microwave discharge at atmospheric pressure have allowed determination of the rate coefficient of the production of N molecules in the B² ∑_u, state with vibrational level ν′ = 0. The N(B²∑_u, ν′) molecules are produced by the reaction in a surface-wave-induced microwave discharge (2450 MHz) sustained in an open-ended dielectric tube. The rate coefficient K (T) has been obtained for ν′ν″ = 0 for different gas temperatures by varying the incident microwave power. The K₀₀(T) values are between 7.10^?10 and 4.10^?10 cm³ s^?1 for the temperature range 2500 to 3450K.     

Vibrational Population of Hydrogen Molecules Excited by an RF Discharge in an Expanding Thermal Arc Plasma as Determined by Emission Spectroscopy

This work is devoted to the determination of the vibrational population of hydrogen molecules in the ground and excited electronic states from the analysis of visible spectra of the H₂ molecules excited by an RF discharge in an expanding thermal arc plasma. Comparison of the experimental results on relative electron-impact excitation cross sections for the transition H₂(X¹Σ, υ⁰ = 0)→ H₂(d³II_u, υ′) with other experiments, and with calculations based on the Franck-Condon principle, shows good agreement. This means, that for plasma under investigation: 1) in the ground electronic state H₂(d³II_u,υ′), only the lowest vibrational level with υ⁰ = 0 is significantly populated, and 2) direct electron exictation of H₂(d³II_u, υ′, υ′) state from the ground state H₂(X¹Σ, υ⁰ = 0) dominates.     

Unimolecular Decay of Metastable Cluster Anions: (O2)N−* → (O2) + O2

Unimolecular dissociation of metastable excited states of (O₂)_n^?* into (O₂) cluster anions has been detected and studied quantitatively for n in the range of 13 to 22. The apparent metastable (decay rates determined increase with cluster size in from ～ 5000 s^?1 (for n = 13) up to ～ 8500 s^?1 for n = 22).     

Desorptions- und Reaktionskinetik der Erdalkalien Calcium und Strontium mit Chlor an Wolfram. Teil I: Chemisches Gleichgewicht der Oberflächenreaktion M + Cl = MCl im stationären Zustand (M = Ca,Sr)

Desorption- and Reactionkinetics of the Alkaline Earth Elements Calcium and Strontium with Chlorine on a Tungsten Surface — Part I: Chemical Equilibrium of the Surface Reaction M + Cl ? MCl in the Steady State (M = Ca, Br) Utilizing positive and negative surface ionization the reaction M + Cl = MCl (M = Ca, Sr) was studied at a hot tungsten surface under steady state conditions. Comparing the results obtained either by simultaneous M- and Cl₂ -exposures or by MCl₂ -exposure the existence of chemical equilibrium could be confirmed for the reaction in the temperature interval 1600 K.2000 K; at higher temperatures this equilibrium can be disturbed considerably by the desorption of the reacting components. From the experimental results we obtained under conditions of chemical equilibrium the energy of dissociation of MCl-molecules in the gasphase (D = (3.9 ± 0.15) eV, D = (4.2 ± 0.15)eV) and in the case of a strong disturbance of the equilibrium the difference between the activation energies of desorption and of dissociation of MCl-molecules on the surface (? - D? = (1.6 ± 0.2) eV, ? - D? = (1.4 ± 0.2) eV).     

Hyperfine Structure of the Configuration lll

The matrix elements for the hyperfine structure of the configuration lll in SL-Kopplung are expressed as linear combinations of the electron coupling constants α_li(10), α_li(01), α_li(12).     

The Influence of Ion – Neutral Collisions in the Plasma Sheath on the Ion Current to an Electrostatic Probe: Monte Carlo Simulation

We have carried out Monte Carlo simulation of the motion of Ar⁺ ions in the space charge sheath surrounding a cylindrical Langmuir probe. From these simulations the percentage of ions crossing the sheath boundary that are collected by the probe have been determined and thus the ion currents to the probe have been calculated. It is shown that the collisions of ions with neutral helium gas atoms in the sheath increase the percentage of ions collected by the probe above that predicted by collisionless orbital motion limited current (OMLC) theory and that the exponent, χ, of the power law dependence, i₊～U, of the ion current, i₊, on the probe voltage, U_p, increases above the value 0.5 predicted by OMLC theory. The results of the simulations are compared with recent Langmuir probe measurements made in flowing afterglow plasmas.     

Desorptions- und Reaktionskinetik der Erdalkalien Calcium und Strontium mit Chlor an Wolfram. Part II: Kinetics of the Elementary Steps of the Surface Reaction M + Cl ⇌ MCl (M = Ca,Sr)

Desorption- and Reactionkinetics of the Alkaline Earth Elements Calcium and Strontium with Chlorine on a Tungsten Surface — Part II: Kinetics of the Elementary Steps of the Surface Reaction M + Cl ? MCl (M = Ca, Sr) Utilizing pulsed molecular-beam-technique the kinetics of desorption of Strontium, Calcium, and Chlorine as well as that of the molecules SrCl and CaCl, which are formed at the hot tungsten surface, was investigated. Thereby, the following values were obtained for the activation energies of desorption: ? = (3.76 ± 0.05) eV, ? = (3.32 ± 0.07) eV, ? = (4.16 ± 0.05) eV, ? = (4.2 ± 0.3) eV and ? = (3.9 ± 0.3) eV. Combining these results with the steady-state-results from part I [1] the temperature dependency of the rate constants of dissociation and recombination of MCl-molecules at the tungsten surface could be determined. The values obtained for the dissociation energies D of SrCl and CaCl on tungsten are (0.5 ± 0.5) eV and (0.3 ± 0.5) eV, respectively. The molecules are stabilized on the surface by the activation barrier for dissociation D? only, which was found to be (2.8 ± 0.5) eV for SrCl and (2.3 ± 0.5) eV for CaCl.     

Nichtstationäre Reflexion und Reemission von Wellen bei Herausbildung elektromagnetischer Strukturresonanzen im Plasma

The nonstationary resonant reflectivity of a density profile is studied which consists of two homogeneous overcritical layers, separated by a vacuum region whose width increases linearly in time. Analytical expressions are derived for the time dependence of both the reflexion coefficient and the cavity field in the case of normal incidence. If the configuration passes through a structure resonance, where the eigenfrequency of the density cavity coincides with the frequency of the external wave, the cavity field is strongly enhanced. The temporary formation and the subsequent decay of this resonant field leads to oscillations of the reflexion coefficient. In the case of a loss-less plasma it may reach the extreme values |R| = 0 |R| ≈ 3 and the moving plasma configuration temporarily acts as an energy storage (|R|² < 1) or an emitter (∣R∣² > 1).     

Central Structure of Dβ Line in Low Pressure T-Tube Deuterium Plasmas

The perturbing ion motion effect on the relative central dip of the H_β (D_β) has been firmly established for numerous values of the reduced mass of the radiating atom – perturbing ion. In this paper the ion motion effect is confirmed for the cases in which the reduced mass and electron densities are constant, while the temperature of plasma is changing. Also a dependence of the dip values on electron density N_e is checked following theoretical results of Demura, Lisitza and Sholin. It is shown that the dip value is a linear function of N, where α is a number close to 1.     

Electron Emission from Clean Solid Surfaces by Fast Ions

Total backward electron yields from 27 elemental, non-crystalline, clean solids were measured during bombardment by H⁺-, H-, H-, He⁺- and Ar⁺-ions in the energy range from 100 keV to 800 keV. The yields were found to exhibit an oscillatory dependence on the atomic number of the target material correlated with the periods of the periodic system. These Z₂-oscillations are relatively insensitive to the type of projectile and the impact energy at the high projectile energies of this experiment. Present theories of electron emission cannot explain the main experimental results. The reasons for this failure are discussed.     

DC Conductivity and Peierls instability in the quasi-one-dimensional organic charge density wave conductor (fluoranthene)2X

Due to the high anisotropy of the dc conductivity (σ_|/σ_⊥ ≈ 10⁴) the organic conductor (fluoranthene)₂X can be regarded as a model system for studying the Peierls instability in quasi-one-dimensional systems. The temperature dependence of the dc conductivity σ_| (T) along the highly conducting crystal axis exhibits the typical behaviour of a quasi-one-dimensional metal with a Peierls transition at about 180 K to a charge density wave (CDW) ground state. As expected for a highly one-dimensional conductor the exact transition temperature depends on three-dimensional coupling effects and therefore on the size of the counterion X^? = PF, AsF, SbF. Above the Peierls transition σ_| (T) can be described quantitatively within a model of CDW fluctuations leading to a pseudo gap in the electronic density of states. Below, the existence of a real energy gap at the Fermi level with a BCS-like temperature dependence determines the charge transport over more than eight orders of magnitude in the electrical resistance. For the intrinsic energy gaps 2 Δ (0), which characterize the ground state of the Peierls semiconductor, values of 120-180 meV have been found for different crystals.     

Some Properties of a Novel Far UV Xenon Excimer Barrier Discharge Light Source

Electrical and optical properties of dielectric barrier Xenon discharge lamps, selectively emitting Xe/172 nm vuv radiation from a multitude of transient discharge filaments have been investigated. The lamps used were uncooled and of the flat panel type with two dielectric quartz barriers and external metal electrodes. Such lamps can be considered as small scale models of much larger flat panel uv lamps. UV emission scales almost linearly with operating frequency below 10 kHz. Both uv emission and uv efficiency rise with increasing gap spacing. The specific 172 nm emission is in the range of 100 mW/cm² for frequencies close to 100 kHz (no lamp cooling). External efficiency at high specific uv emission is close to 10%. Higher external efficiencies up to 20% are possible at lower frequencies of a few kHz, but at reduced specific uv flux.     

Experimentelle Untersuchungen zur Ionisierung und Umladung von Alkanolen durch 6-25 keV Wasserstoffionen

Experimental Investigations of Ionisation and Charge-transfer of Alcohols by 6-25 keV Hydrogen Ions Ionisation and charge-transfer cross sections were measured for the interaction of H⁺, H and H ions (in the energy range 6-25 keV) with alcohols (methanol-octanol). The cross sections depend significantly on the target molecular structure like molecular length, ionisation potential, polarizability and atomic bonds in the target molecule.     

Sea Level Muon Spectrum Derived from Bugaev Model

The pion and kaon spectra in the atmosphere are derived from primary nucleon spectrum determined by GRIGOROV et al.; they satisfy the relations N(E_π) dE_π = 0.187 EdE_π and N(E_k) dE_k = 0.017 E dE_k, respectively. By using the pion-kaon atmospheric diffusion equation the sea level muon spectrum is calculated and the result compared with the magnetic spectrograph data of ALLKOFER et al. and AYRE et al.     

On a Mechanical Model of the Bopp-Podolsky Potential

For an arbitrary given distribution of dislocations and disclinations the general state of stress of a mechanical continuum is investigated. The medium is reacting with stresses and momentum stresses (Cosserat continuum). By means of differential geometry it is shown that the deformations _ik and ?_ik of two arbitrary materials with identical distributions of defects differ merely by a displacement field u_i(x^r, t). If _ik are the eigendeformations of an isotropic medium, then in the linear theory the field u_i of a Cosserat continuum can be separated from _ik. If the problem is static the u_i obey the potential equation of Bopp-Podolsky electrodynamics. As source only torsion (dislocations and torsion of disclinations) is acting. To give an example the field u_i for straight dislocations and disclinations is calculated. Especially the problem of singularities is discussed.     

Nachweis von radikalischen Zersetzungsprodukten in CCl4-Entladungen mit der EPR-Spektroskopie

Among the dissociation products of a r.f. discharge in CCl₄-vapour the radicals CCl₃ and Cl₂- have been identified by EPR-spectroscopy after condensation at 80 K. The gas-phase reaction CCl₃ + O₂ → CCl₃OO has been used to estimate the CCl₃ concentration to be approximately 5 · 10¹³ radicals/cm³ at p = 55 Pa. The life-time of CCl₃-radicals is governed by the rate of desactivation of some exited species (eg. CCl₄*) via . At a pressure p = 55 Pa a half-life of CCl₃-radicals of τ1/2 = 80 ms has been found.     

Anwendung der GRYZINSKY-Theorie zur Berechnung der Ionisierungs- und Umladungwirkungsquerschnitte für die Wechselwirkung von Wasserstoffionen und Alkanolmolekülen

An Application of GRYZINSKY -theory to Calculations of Ionisation and Charge-transfer Cross Sections for the Interaction of Hydrogen Ions with Alcohol Molecules Ionisation and charge-transfer cross sections were calculated for the interaction of H⁺, H and H ions (energy range 5-25 keV) with alcohols (methanol-butanol). A modified GRYZINSKY approximation is used for the calculation of the cross sections. The calculated values have been compared with experimental determined cross sections. The agreement between experimental results and theoretical results is satisfactory.     

On a simple formula for the energy of the lowest octupole state

A recently introduced way of parameterizing the energies of 3 states in many even-even nuclei, based on the microscopic structure of the low-energy octupole mode, is slightly modified so it now includes all (non-doubly magic) nuclei with A ? 30.     

A novel probe for determination of electrical surface potential of surfactant micelles: N,N'‐di‐n‐octadecylrhodamine

The peculiarities of the structure of the fluorescent dye N,N'‐di‐n‐octadecylrhodamine advantage its using as an interfacial acid–base probe in aqueous micellar solution of colloidal surfactants. Two long hydrocarbon tails of the dye provide similar orientation of both cation and zwitterion on the micelle/water interface, with the ionizing group COOH exposed to the Stern region in all the systems studied. Further, the charge type of the acid–base couple, A⁺B^±, ensures similar values of the ‘intrinsic’ contribution, pK, to the ‘apparent’ pK value in micelles of different surfactants. This makes the indicator suitable for determination of electrical surface potentials, Ψ. The pKs have been obtained in cationic, anionic, zwitterionic, and nonionic surfactant systems, at various salt background. In total 17 systems were studied. At bulk counterion concentration of ca. 0.05 M, the pK values vary from 2.14 ± 0.07 in n–C₁₈H₃₇N(CH₃)Cl^– micelles to 5.48 ± 0.06 in n–C₁₆H₃₃OSONa⁺ micelles. The Ψ values, corresponding to the Stern region of micelles, have been evaluated as Ψ = 59.16 pK–pK for T = 298.15 K. The pK parameter was equated to the average value of 4.23 in nonionic surfactants (4.12–4.32, depending on the surfactant type). For cetyltrimethylammonium bromide and sodium n‐dodecylsulfate micelles, the Ψ values (±(7–11) mV) appeared to be +118 mV and at bulk Br^? concentration 0.019 M and ?76 mV at bulk Na⁺ concentration 0.020 M, respectively. This satisfactorily agrees with the theoretical values +111 and ?84 mV, estimated using the Oshima, Healy, and White equation for these well‐defined colloidal systems. Finally, not only absorption, but also fluorescence spectra display the same response to changes in bulk pH. Copyright © 2007 John Wiley & Sons, Ltd.     

An ab initio study of CX3‐substitution (X = H,F, Cl,Br, I) effects on the static electric polarizability and hyperpolarizability of diacetylene

We report a systematic ab initio and density functional theory (DFT) study of the electric properties of the X₃C? C≡C? C≡C? H (X = H, F, Cl, Br, and I) sequence of substituted diacetylenes. We rely on finite‐field Møller–Plesset perturbation theory and coupled‐cluster calculations with large, flexible basis sets. Our best values at the second‐order Møller–Plesset perturbation theory level for the mean dipole polarizability and second hyperpolarizability are $\overline {{\alpha} } $ /e²aE = 64.46 (? CH₃), 65.59 (? CF₃), 110.11 (? CCl₃), 138.90 (? CBr₃), 184.98 (? CI₃) and $\overline {{\gamma} } $ /e⁴aE = 21020 (? CH₃), 13469 (? CF₃), 32708 (? CCl₃), 57599 (? CBr₃), and 105251 (? CI₃). For comparison, the analogous MP2 values for diacetylene [P.Karamanis and G.Maroulis, Chem. Phys. Lett. 2003 , 376, 403.] are $\overline {{\alpha} } $ /e²aE = 49.17, and $\overline {{\gamma} } $ /e⁴aE = 16227. For the mean first hyperpolarizability we report $\overline {{\beta} } $ /e³aE = ?205.8 (? CH₃), ?55.7 (? CF₃), 120.8 (? CCl₃), 443.8 (? CBr₃), and 725.4 (? CI₃). Copyright © 2010 John Wiley & Sons, Ltd.