Recombination in nonideal ion gas discharge afterglow plasma

Recombination rates in ion plasma are presented that are obtained by processing experimental data on gas discharge afterglow in fluorine and sulfur hexafluoride media. A theoretical explanation is given to the slowing down of the recombination rate of plasma in such media as the degree of Coulomb nonideality of the media increases. An additional factor for the suppression of recombination—solvation of ions—is considered. It is shown that, in the case of discharge afterglow plasma in a fluorine medium, the process of recombination proceeds in two stages with the formation of intermediate metastable ion pairs produced by ion-molecule clusters. In a sulfur hexafluoride medium, the formation of such pairs does not have a significant effect on the recombination rate.     

Methane Conversion in the Flowing Afterglow of a Dinitrogen Microwave Plasma: Initiation of the Reaction

The reaction of methane in the nitrogen afterglow is studied by combination of direct measurements and computer experiment. The experimental data were obtained by optical emission spectroscopy of the discharge, by gas chromatography of resulting stable products and by probe diagnostics of charged species in afterglow plasma. The simulation was based on a macroscopic kinetic approach covering 24 species and 61 reactions with input data given by the afterglow experiment. In the present stage of the modelling the initiation of methane conversion was studied. It was found that, contrary to active discharge, in the afterglow plasma the active neutral species (mainly excited dinitrogen molecules) are most important for the dissociation of methane into CH_x and H radicals.     

Recombination population of excited states of the hydrogen atom in an He-H<Subscript>2</Subscript> plasma

The population of excited states of the hydrogen atom in an afterglow plasma produced by a pulsed discharge in helium (40 Torr) with a small admixture of hydrogen ([H₂] ≈ 10¹² cm^?3) has been studied spectroscopically. The contribution from electron-ion recombination Γ ₃ ^rec to the production rate of atoms H(n = 3) has been separated. On the basis of an experiment in which the response of the spectral line intensities to the perturbation of the electron temperature in the afterglow phase was observed, the dependence Γ ₃ ^rec (T _e ～ T _e ^?(0.9–1.0) has been obtained in the region kT _e = 0.026–0.064 eV.     

On the ultracold plasma evolution

The time evolution of the Coulomb system whose initial total energy is zero is considered. The solution for a system of 2000 particles in the range of 8000 inverse plasma frequencies was obtained by themolecular dynamicsmethod. It is shown that under conditions typical of experiments with ultracold plasma the nonideality parameter of the plasma cannot reach large values due to recombination heating, and the relaxation process itself is not described within the conventional model of three-body recombination.     

Plasma sterilization using the RF glow discharge

In the present work, glow discharge oxygen plasma was used to sterilize the Pseudomonas aeruginosa on the polyethylene terephthalate (PET) sheets. In a self-designed plasma reaction equipment, active species (electron, ion, radical, UV light, etc.) were separated effectively, and the discharge area, afterglow area and remote area were plotted out in the plasma field. Before and after plasma treatment the cell morphology was studied by scanning electron microscopy (SEM). The results showed that after treatment of 30 s the germicidal effect is 4.26, 3. 84, 2.61, respectively in the three areas on the following conditions: discharge power was 40 W and gas flux was 20 cm³/min. SEM results revealed the cell morphology before and after plasma treatment. The walls or cell membrane cracking was testified by determining the content of protein using coomassie light blue technique. The results from electron spin resonance spectroscopy (ESR) and double Langmuir electron probe showed that electron, ion and oxygen free radical played important roles in sterilization in the discharge area, but only oxygen radicals acted to sterilize the bacteria in the afterglow area and the remote area.     

On the description of multiple measurements of an unstable state

The nondecay probability of an unstable particle at a definite moment of time is investigated provided this particle existed at all earlier observation moments separated with the time interval Δ. Using the usual postulates for quantum measurements it is proved that this probability is described by the exponential function of Δ>0, and it tends to 1 as Δ → 0. An approximate formula is found for the effective decay width Γ(Δ) appearing in the case of multiple measurements. It is shown that Γ(Δ) → 0 as Δ → 0. For Δ → ∞, the width Γ(Δ) → Γ₀, with Γ₀ being the standard decay with in Weisskopf-Wigner theory. At finite δ's Γ(Δ) may be smaller or greater than Γ₀ depending on the parameters of the theory.     

Recombination processes and quenching of negative afterglow by microwaves — Ne,Ne + He

Quenching of the afterglow of an interrupted negative glow by application of microwaves to the decaying plasma has been observed. The time dependences of Ne atomic spectral line intensities show that two distinct groups of spectral lines, each group having its own time dependence in the afterglow, are emitted. Both the potential curves and energy level positions known for Ne ₂ ⁺ and Ne₂ are discussed with respect to the observed effects. The time dependence of Ne spectral lines cannot be explained by the temperature dependence of recombination coefficients only.The enhanced Mo spectral line emission (material evaporated from the cathode) caused by microwaves during the discharge period or after current cutoff, makes it possible to estimate the electron temperature increase and relaxation during and after the microwave pulse.     

Measurement of Excited States Density and the VUV-Radiation in the Pulsed Xenon Medium Pressure Discharge

Time resolved absolute density measurements of the 1s5 (metastable) and 1s4 (resonance) level in the positive column of a pulsed xenon gas discharge for gas pressures between 1 and 40 Torr and currents between 100 and 300 mA are presented. The densities ranged from 1 × 10¹¹ to 5 × 10¹² cm^?3 and were found to be ten times larger in the afterglow than in the active part of the discharge. The enhanced radiation obtained in the afterglow in the near infrared regions as well as in the VUV region is caused by a dissociative recombination and formation of excimer states.     

Critical angles and minimum yields for planar channeling

Abstract

Local regions on the surface of a sample of ZnO: Zn phosphor powder were deteriorated by low energy heavy ions to a depth of a few hundred Angstrom units. These regions behave as ‘thin films’ in which a negligible small amount of light is produced when an energetic projectile passes through it. The sample was then scanned across energetic ion beams. The scintillation response diminished when the beam impinged onto a film. The decrease, ΔL, in light intensity is the amount of light produced in a phosphor region whose thickness is equivalent to the film thickness. For ¹H and ⁴He the luminescent efficiency, ΔL/ΔE (the ratio of the light produced to the observed energy loss), is approximately independent of energy indicating that the scintillation response depends primarily on the inelastic projectile-electron collisions rather than the elastic projectile target atom encounters.

At a given velocity, a plot of ΔL versus the atomic number of the projectile exhibits oscillatory structure for which a tentative explanation is suggested.     

Recombination of electrons with highly charged heavy ions at very low energies

Recombination of highly charged ions with free electrons is studied in merged-beams experiments at the UNILAC accelerator in Darmstadt and at the heavy-ion storage ring TSR in Heidelberg. Unexpected high recombination rates are observed for a number of ions at very low energiesE _cm in the electron-ion center-of-mass frame. In particular, theoretical estimates for radiative recombination are dramatically exceeded by the experimental recombination rates of U²⁸⁺ ions nearE _cm=0 eV. The observations point to a general phenomenon in electron ion recombination depending onE _cm, on the ion charge state, and possibly also on electron density, electron beam temperature, and strength of external magnetic fields.     

Intermolecular potentials for ammonia based on the test particle model and the coupled pair functional method

The intermolecular interaction ΔE in (NH₃)₂ is investigated on the SCF level, with inclusion of correlation effects by means of the CPF method and within the simple test particle model. Whereas the linear hydrogen bonded structure is favoured on the SCF level, ΔE = -7·65 kJ mol^-1, the most stable geometry on the highest level of theory is a cyclic structure, ΔE = -12·96 kJ mol^-1. The minimum is very shallow and allows for appreciable angular motions. The test particle model reproduces the general features of ΔE but shows deviations in details. The computed potentials are used in MD simulations to compute static and dynamic properties of liquid NH₃. Good agreement with available experimental results is obtained throughout.     

Energy analysis of protons emitted from Nd:YAg laser-generated plasmas

Hydrogenated targets have been irradiated in vacuum with the pulsed Nd:YAg laser at intensities of the order of 10¹⁰ W/cm². The laser-generated plasma, produced by the interaction with the solid, emits protons and other ions along the normal to the target surface. Ion collectors and ion energy analyzer were used to measure the current, the angular emission and the energy distributions of the emitted protons. Time-of-flight measurements, Coulomb–Boltzmann-distributions and the fits of experimental data were also used in order to evaluate the equivalent ion plasma temperature and the ion acceleration developed in the non-equilibrium-pulsed plasma.     

Investigations on Afterglows of Neon Gas Discharges

We report on the experimental and numerical investigations on afterglows of neon gas discharges, which are performed at the Eindhoven University of Technology. The studied gas pressure range extends from 1 to 100 torr, the discharge current from 1 to 100 mA. The densities of the 1s-levels are measured with the help of the selective excitation spectroscopy (fluorescence technique). In this way a great number of decay curves of the 1s-densities have been measured in the afterglow of neon gas discharges. From these curves the diffusion coefficient of the metastable 1s-atoms, the coefficients of atomic collisional transfer between the 1s₅- and 1s₄-level, as well as the three body collision coefficient between metastable 1s₅-atoms and neon ground state atoms have been determined. Besides these experiments a numerical model of the neon afterglows has been developed. With this model the afterglow phenomena can be simulated and the influence of the particular processes on the whole afterglow can be studied conveniently. Comparison is made between the experimentally and numerically obtained decay curves. For the application of the numerical model a number of starting conditions, such as radial density profiles, gas temperature, (relative) densities of the 1s-levels, have been measured. Results of these measurements are presented. Also with the help of the selective excitation spectroscopy the coefficients of atomic collisional transfer between the 2p-levels have been measured in the afterglow. From these results, together with the measured (relative) intensities of the neon spectral lines in the afterglow the partial recombination coefficients for the 2p-levels were calculated.     

Assessment of a composite CC2/DFT procedure for calculating 0–0 excitation energies of organic molecules

The task to assess the performance of quantum chemical methods in describing electronically excited states has in recent years started to shift from calculation of vertical (ΔE_ve) to calculation of 0–0 excitation energies (ΔE₀₀). Here, based on a set of 66 excited states of organic molecules for which high-resolution experimental ΔE₀₀ energies are available and for which the approximate coupled-cluster singles and doubles (CC2) method performs particularly well, we explore the possibility to simplify the calculation of CC2-quality ΔE₀₀ energies using composite procedures that partly replace CC2 with more economical methods. Specifically, we consider procedures that employ CC2 only for the ΔE_ve part and density functional theory methods for the cumbersome excited-state geometry optimisations and frequency calculations required to obtain ΔE₀₀ energies from ΔE_ve ones. The results demonstrate that it is indeed possible to both closely (to within 0.06–0.08 eV) and consistently approximate ‘true’ CC2 ΔE₀₀ energies in this way, especially when CC2 is combined with hybrid density functionals. Overall, the study highlights the unexploited potential of composite procedures, which hitherto have found widespread use mostly in ground-state chemistry, to also play an important role in facilitating accurate studies of excited states.     

Kinetic processes in a nonideal Rydberg matter

A kinetic model is developed to describe ultracold nonideal Rydberg plasmas, which allows all stages of the generation and decay of such a plasma to be sequentially traced. The plasma kinetics is considered on the basis of available experimental data corresponding to a nonideality parameter of γ ～ 1. The results of theoretical analysis are in good agreement with experiment. Calculations show evidence of a significantly decreased recombination rate and, hence, of the possible formation of a metastable structure in the plasma under consideration. The distribution of the number of excited atoms is determined for the plasma with N_e = N_i = 7 × 10⁵ and E_e = 9 K. The observed behavior of the number and density of particles as functions of the time and principal quantum number is explained. It is suggested that the distribution of excited atoms for the given parameters has a maximum for the state with k = 25.     

Is the Two-Dimensional One-Component Plasma Exactly Solvable?

The model under consideration is the two-dimensional (2D) one-component plasma of point-like charged particles in a uniform neutralizing background, interacting through the logarithmic Coulomb interaction. Classical equilibrium statistical mechanics is studied by non-traditional means. The question of the potential integrability (exact solvability) of the plasma is investigated, first at arbitrary coupling constant Γ via an equivalent 2D Euclidean-field theory, and then at the specific values of Γ = 2*integer via an equivalent 1D fermionic model. The answer to the question in the title is that there is strong evidence for the model being not exactly solvable at arbitrary Γ but becoming exactly solvable at Γ = 2*integer. As a by-product of the developed formalism, the gauge invariance of the plasma is proven at the free-fermion point Γ = 2; the related mathematical peculiarity is the exact inversion of a class of infinite-dimensional matrices.     

The Dual Mode Microwave Afterglow Apparatus for Measuring the Electron Temperature Dependence of the Electron‐Ion Recombination

Three dual mode microwave apparatus (one using S ‐band and two using X ‐band) have been developed to determine ambipolar diffusion and electron‐ion recombination rates under conditions such that T_gas = 300K and T_e is varied from 300 K to 6300 K, in the afterglow period of the dc glow discharge. TheTM₀₁₀ cylindrical cavity (in S ‐band) and TM₀₁₁ open cylindrical cavity (X ‐band) are used to determine the electron density during the afterglow period and a non‐resonant waveguide mode is used to apply a constant microwave heating field to the electrons. To test the properties of the apparatus the neon afterglow plasma has been investigated. At T_e = 300 K a value of α (Ne⁺₂) = (1.7± 0.2) × 10^–7cm³/s is obtained which is in good agreement with values of other investigators. Also similar variations of α as T^–0.4_e (S ‐band) and as T^–0.42_e (X ‐band) obeyed over the range 300 ≤ Te ≤ 6300K are in good agreement with some other previous measurements. The simplicity of the X‐band microwave apparatus also allows the measurements of the gas temperature dependency and the study of electron attachment and may be used simultaneously with optical or mass spectrometry investigations. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Vertex functions as a factor of enhancing electron-electron attraction in d-wave channel of the “Coulomb” superconductivity mechanism

It is shown that many-particle Coulomb correlations described by Coulomb vertex functions Γ_c in layered high-T _c superconducting metal oxide cuprates substantially enhance effective electron-electron attraction in the d-wave Cooper-pairing channel. This attraction is due to the combined action of a strong in-layer anisotropy of the quasi-two-dimensional electronic spectrum and the suppression of a screened Coulomb repulsion for small transferred momenta in small-angle charge-carrier scattering from long-wavelength charge-density fluctuations. Such a “Coulomb” mechanism of anisotropic Cooper pairing may provide high superconducting transition critical temperatures (T _c ≥100 K) for optimum-doped cuprates.     

Multichannel energy analysis of the ion flux from a theta pinch

The ion flux parallel to the axis of a linear theta pinch (p ₀=10–30 μ D₂) is analyzed by a new 10-channel energy spectrometer (E=1–10keV). Time resolved energy spectra were measured in each single discharge. It can be shown experimentally that neutral gas, electrons and magnetic fields considerably influence the flux distribution. The measured energy spectra (E≦15 keV) are broad and have no ion groups. At 10 μ D₂ dn/dE is proportional to exp {?E/ē} forE≧3 keV, whereē≈1 keV. For 10, 20 and 30 μ D₂ ē is about equal to thekT deduced from the neutron flux. The time developments of the neutron and ion fluxes (in the range 1–10 keV) are correlated. For the initial phase of the discharge the measuring results are incompatible with relaxation by Coulomb collisions. It seems rather, that there is anomalously fast relaxation due to a microinstability. After the anomalous relaxation the end losses, particularly of the slower ions, continue as a result of Coulomb collisions. This produces increasing distortion of theE-distribution with smallE, which leads to a second microinstability with loss of energetic ions in particular (probably a loss-cone type).     

Production of the excited Ne(2p 5 3p) atoms by dissociative recombination in the afterglow of high frequency neon discharge

Experimental results are presented of the measurements of the population of the Ne(2p ⁵ 3p) atoms from the time dependences of the relative intensities of the spectral lines corresponding to 3s -3p transitions in the afterglow period of a high frequency neon glow discharge at pressures from 266 Pa to 4 kPa. The partial recombination coefficients were determined from these measurements as a function of gas pressure and they are compared with measurements of other authors. It is shown that at low gas pressures the Ne(2p ⁵ 3p) atoms are also populated only in the dissociative recombination in spite of the fact that the dominant loss process of charged particles is the ambipolar diffusion.