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.     

Diffusion Model of Saturation Current Collection by a Planar Langmuir Probe in a Strong Magnetic Field

Plasma presheath and saturation current collection by a planar Langmuir probe in a strong magnetic field perpendicular to the probe surface ares described with the diffusion model. The model takes into consideration the geometry of the probe, that is its size and shape, and dependence of the cross-field charged particles' transport into the effective collection region of the probe on the parallel-field transport to the probe. Experimental study of planar Langmiur probe I—V characteristics in D.C. discharge argon plasma in strong magnetic fields confirms the possibility of deriving the cross-field diffusion coefficient, D, from the measured electron satuation current. Additional dependence of the electron saturation current on the parallel-field diffusion coefficient, D, and the ion temperature, T_i, derived in the approximate Stangeby's study using the diffusion model of current collection by a planar surface (Stangeby, P. C., J. Phys. D: Appl. Phys. 15 (1982) 1007) can be eliminated with more rigorous calculation. Series of measurements on two neutral pressures and various magnetic fields gave reproducible values of D, approximately given by relation D ≈ (δn/〈n〉) k_BT_e/(eB).     

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).     

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.     

The reaction of •OH with O2, the decay of O and the pKa of HO – interrelated questions in aqueous free‐radical chemistry

In the reactions of ozone with organic compounds in aqueous solution, O is an abundant intermediate. A basic aspect of its conversion into ^?OH is addressed here. The reactions O^?? + O₂ ? O (1), H⁺ + O^?? ? ^?OH (8), ^?OH + O₂ ? HO (6), and H⁺ + O ? HO (5) are interconnected by a thermodynamic cycle. For equilibria (1) and (8) reliable equilibrium constants, and hence Gibbs energies are available (ΔG⁰(1) = ?32 kJ mol^?1, ΔG⁰(8) = 67 kJ mol^?1). For reaction (6), a Gibbs energy of ΔG⁰(6) = 47 kJ mol^?1 (K₆ = 10^?8.2 M) has now been calculated by G1. From the thermodynamic cycle one hence arrives at ΔG⁰(5) = ?12 kJ mol^?1. This relates to pK_a(HO) = ?2.1. Thus, the HO radical is a very strong acid. This value agrees with a value of ?2.0 obtained from the Bielski and Schwarz relationship for pK_a values of O_xH_y compounds. Reaction (6) must be very slow, 0.1 < k₆ < 10⁴ M^?1 s^?1. Copyright © 2010 John Wiley & Sons, Ltd.     

A non‐enzymatic model based on an acyl transfer reaction for the formation of energy‐rich acetyl phosphate in organic solvents and in a biphasic system

The formation of acetyl phosphate (AcP), an energy‐rich phosphate compound, was studied through the reaction of 2,4‐dinitrophenyl acetate with H₂PO solubilized with Kryptofix® 222 or as a tetra‐n‐butylammonium ((n‐C₄H₉)₄N⁺) salt in organic media. The results indicated that the rate of the reaction in acetonitrile is strongly inhibited by the addition of water, suggesting that the water added to the medium preferentially solvates the H₂PO anion, inhibiting its action as a nucleophile and allowing it to act as a general base catalyst, which leads to the hydrolysis of the ester. The utilization of various organic solvents in the acetyl transfer process demonstrated that the specific interaction of the solvent with water accelerates the process, by desolvation of H₂PO, which can act as a nucleophile. Finally, a formation/transformation cycle of AcP was studied in a biphasic system (water/CH₂Cl₂) using Kryptofix® 222 and (n‐C₄H₉)₄N⁺BF as both the carrier and solubilizing agent for KH₂PO₄. Copyright © 2010 John Wiley & Sons, Ltd.     

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).     

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.     

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.     

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.     

Primary kinetic hydrogen isotope effects in deprotonations of a nitroalkane by intramolecular phenolate groups

Rate constants and kinetic isotope effects have been determined for the formation of nitronate anions from the ethers 1‐(2‐methoxyphenyl)‐2‐nitropropane, 7 (X = H, L = H and D) and 1‐(2‐methoxy‐5‐nitrophenyl)‐2‐nitropropane, 7 (X = NO₂, L = H and D), and from the corresponding phenols, 1‐(2‐hydroxyphenyl)‐2‐nitropropane, 3 (X = H, L = H and D), and 1‐(2‐hydroxy‐5‐nitrophenyl)‐2‐nitropropane, 3 (X = NO₂, L = H and D), in aqueous basic medium. For the ethers 7 , rates of deprotonation by hydroxide are comparable with those found for deprotonations of 2‐nitropropane, with k^H/k^D (25 °C) = 7.7 and 7.8, respectively. In both the cases, the isotope effects are conventionally temperature dependent. For the corresponding phenols 3 , conditions have been established under which the deprotonations of the nitroalkane are dominated by intramolecular deprotonation by the kinetically first‐formed phenolate anion, with an estimated effective molarity EM ～ 250. For 3 (X = H, L = H or D), k^H/k^D (25 °C) = 7.8, with E ? E = 6.9 kJ mol^?1 and A^H/A^D = 0.5. For 3 (X = NO₂, L = H or D), rates of intramolecular deprotonation are reduced 30‐fold, and an elevated kinetic isotope effect is found (k^H/k^D (25 °C) = 10.7). Activation parameters (E ? E = 17.8 kJ mol^?1 and A^H/A^D = 0.008) are compatible with an enhanced tunnelling contribution to reactivity in the H‐isotopomer. Copyright © 2009 John Wiley & Sons, Ltd.     

Photoionization and photoelectron angular distribution for H2

Photoionization of H₂(¹Σ_g⁺) in a vibrational υ″ and rotational N″ state into H₂⁺(²Σ_g⁺) in a vibrational υ′ and rotational N′ state is studied theoretically. The differential cross section, after summing over the final states, is expressed in the well-known simple form of $\text{(}\text{σ}{}_{\mathrm{T}}\text{4π}\text{)[1 + βP}{}_2\text{(}\text{cos}\text{θ)]}$. Parallel expressions are obtained for H₂⁺ in a specific υ′ state (in terms of σ(υ′) and β(υ′)) and for H₂⁺ in a rotational fine level υ′N′ (in terms of σ(υ′N′) and β(υ′N′)). Asymmetry parameters β, β(υ′) and β υ′N′), which are expressed in terms of Racah and Clebsch-Gordan coefficients and electronic transition moments, can be reduced approximately to 2 lineary polarized light and to -1 for unpolarized light. Using single-center electronic wave functions and including partial eaves l = 1, 3, and 5, σ(υ′) and β(υ′) are computed as a function of υ′ at 584 Å. The computed σ(υ′) divided by the Frank-Condon overlap, in agreement with experimental results, increases monotonically with υ′; σ_T and β are computed in the incident photon energy range of 600–4000 Å and the results compare favorably with previous calculations.     

Effects of ortho‐substituents in SE1 protonolysis of phenylmercuric chloride

The kinetics of the reactions of o‐substituted phenylmercuric chlorides, o‐RC₆H₄HgCl (R = CH₃, H, C₂H₅O, CH₃O, C₆H₅, F, COOC₂H₅, Cl, Br, CF₃, NO₂), with hydrochloric acid in 80% aqueous dioxane in the presence of NaI were studied. The reactions are of the first order. The rate constant at 40°C decreases in the order of R: CH₃ > H > C₂H₅O > CH₃O > C₆H₅ > F > COOC₂H₅ > Cl > Br > CF₃ > NO₂. The analysis of effects of those o‐substitutes is carried out through multiple regression of log k/k_H with the corresponding inductive substituent constants σ_I and the various resonance substituent constants σ, σ_R(BA), σ, σ and σ_x, and the corresponding Swain–Lupton field effect constant and resonance effect constant . The results showed that o‐substituent intramolecular coordination with the neighbor mercury (field effect) is the main effect in effects of o‐substituents on rate of the S_E1 protonolysis. Copyright © 2007 John Wiley & Sons, Ltd.     

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.     

Gas‐phase basicities of acetophenones toward lanthanum cation [La(OMe)]

The relative free energy changes (lanthanum cation basicity, LaCB[L₂]) for the reaction [La(OMe)₂]L ? La(OMe) + 2L were determined in the gas phase for m‐ and p‐substituted acetophenones based on the measurement of ligand exchange equilibria using an FT‐ICR mass spectrometer. The substituent effect on ΔLaCB[L₂] of acetophenone is described in terms of the Yukawa–Tsuno equation, ΔG = ρ(σ° + r⁺ Δ σ ), with a ρ value of ?11.2 and an r⁺ value of 0.49. From this result, a ρ value of ?7.0 and an r⁺ value of 0.49 were estimated for the monomeric complex [LLa(OMe)] with the aid of theoretical calculations. This ρ value was found to be significantly smaller than that for protonation, and even smaller than Li⁺ basicity. Such a small ρ value has been attributed to the largely ionic (ion–dipole interaction) nature of the bonding interaction between La(OMe) and the carbonyl oxygen atom and, in part, to the long distance between La(OMe) and the substituent. Contrary to the ρ value, the r⁺ value is identical in both La(OMe) and Li⁺ basicities, suggesting that the r⁺ value of 0.49 can be regarded as a limiting one in a series of Lewis cation basicities of the acetophenone system, H⁺ (0.86) > Me₃Si⁺ (0.75) > Me₃Ge⁺ (0.71) > Cu⁺ (0.60) > Li⁺ = La(OMe) (0.49). Since the binding interaction between La(OMe) or Li⁺ and a neutral ligand is mostly electrostatic, the moderate r⁺ was interpreted to result from the redistribution of the induced positive charge within the acetophenone moiety upon binding with a metal ion rather than transfer of positive charge from a metal ion to the aromatic moiety. Copyright © 2010 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.     

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).     

Effects of substituents on activation parameters in SN2 reactions at aliphatic carbon in solution

Changes of the activation parameters in aliphatic S_N2 reactions with anionic and neutral nucleophiles in various solvents, ΔH^≠ and ΔS^≠, were correlated with σ constants of the substituents. The resultant δΔH^≠ and δΔS^≠ reaction constants are linearly related for variations of substituents at the substrate, leaving group and nucleophile. Correlations of δΔH^≠ versus δΔS^≠ allow the estimation of the contribution of changes of the internal enthalpy, δΔH, to the enthalpy reaction constant, δΔH^≠, which gives a single linear dependence on the Hammett ρ reaction constants. The deviations from the dependence of δΔH versus ρ can be interpreted in terms of changes in the transition state structure in S_N2 reactions. The results obtained show that the substituent effects on the charge development in the transition state are governed by the magnitude of δΔH. Copyright © 2009 John Wiley & Sons, Ltd.