Collision transfers between CdH A 2Πυ′ = 0 rotational states induced by He or Ar

CdH is obtained by radiofrequency discharge in Cd vapor mixed with 5% H₂ in He or Ar. It is selectively excited by a pulsed dye laser to A ²Π_{$\text{1}\text{2}$,$\text{3}\text{2}$} υ′ = 0, J′ = 0.5–16.5. Collision cross sections are measured from several J′ values corresponding to rotational transfers observed up to ΔJ′ = ±7. The total collision cross sections are smaller with He than with Ar. They decrease as J′ increases. The levels of the same electronic parity as the initial level are strongly privileged for high J′ with He, much less with Ar. The polarization of the initial lines decreases appreciably for high J′ with the Ar pressure, much less with the He pressure. Small spin transfers are observed from Π_{$\text{3}\text{2}$} to Π_{$\text{sol:1}\text{2}$}. The experimental results, especially the propensities, are justified using the Born approximation as developed in previous papers. Its validity is discussed in comparing the effects of He and Ar.     

Comparison of Gasoline-Ranged <Emphasis Type="Italic">n</Emphasis>-Alkanes Conversions Using Dielectric Barrier Discharge: A Kinetic Study

Here, we compared the conversion of gasoline-ranged n-alkanes (C₆–C₉) using dielectric barrier discharge. For an energy density of ~68 J/L and an initial n-alkane concentration of ~230 ppm, when carbon number increased from 6 to 9, the energy efficiency of n-alkane conversion increased from 117 to 240 mmol/kWh, CO _x selectivity decreased from 46 to 20%, and ozone concentration increased from 216 to 240 ppm. The effect of energy density and initial n-alkane concentration were also investigated. The understanding of initial step of conversion was greatly aided by a proposed kinetic model. The pathways of consecutive reactions from the initiation to products were also discussed.     

On the photoionization of barium by HeI resonance radiation

The branching ratio between the two components of the 6² P state of Barium ions, produced by photoionization with Hel light (21.22 eV) from a discharge source, can be changed by a factor of two or more by changing the He discharge conditions.     

Emission spectroscopic studies of Grimm-type glow discharge plasma with argon-helium gas mixtures

The effect of argon/helium pressure ratios on the emission intensity of various Ar II lines is investigated for a Grimm-type glow discharge radiation source, operated with Ar-He mixtures. The relative intensities of the Ar II lines are altered significantly by mixing helium with argon. It is found that the population of the Ar⁺ excited states can be redistributed through He-Ar collisional energy transfer. The energy level of the He singlet metastable state (¹S₀,20.62 eV) is very important for these processes. If the excitation energy of Ar II lines is higher than that of the He singlet metastable, strong quenching of the Ar II line intensity is observed. However, when the excitation energy is slightly lower, some of the Ar II lines are enhanced by adding helium to the argon plasma. Energy exchanges between the Ar⁺ doublet term states and the He singlet metastable are favoured because the total spin remains unchanged before and after the He-Ar collisions. Furthermore, the helium mixing also exerts a great influence on the emission intensities of the elements sputtered from the cathode of the discharge lamp. The enhancement of Al I and Al II emission intensities at suitable Ar-He mixture ratios is discussed for when aluminum is employed as a cathode material.     

New power source from fractional quantum energy levels of atomic hydrogen that surpasses internal combustion

Extreme ultraviolet (EUV) spectroscopy was recorded on microwave discharges of helium with 2% hydrogen. Novel emission lines were observed with energies of q·13.6 eV where q=1,2,3,4,6,7,8,9, or 11 or these lines inelastically scattered by helium atoms wherein 21.2 eV was absorbed in the excitation of He (1s²) to He (1s¹2p¹). These lines were identified as hydrogen transitions to electronic energy levels below the ‘ground’ state corresponding to fractional quantum numbers. Significant line broadening corresponding to an average hydrogen atom temperature of 33–38 eV was observed for helium–hydrogen discharge plasmas; whereas pure hydrogen showed no excessive broadening corresponding to an average hydrogen atom temperature of ≈3 eV. Since a significant increase in H temperature was observed with helium–hydrogen discharge plasmas, and energetic hydrino lines were observed at short wavelengths in the corresponding microwave plasmas that required a very significant reaction rate due to low photon detection efficiency in this region, the power balance was measured on the helium–hydrogen microwave plasmas. With a microwave input power of 30 W, the thermal output power was measured to be at least 300 W corresponding to a reactor temperature rise from room temperature to 900 °C within 90 s, a power density of 30 MW/m³, and an energy balance of about −4×10⁵ kJ/mol H₂ compared to the enthalpy of combustion of hydrogen of −241.8 kJ/mol H₂.     

Numerical Study of HBr/He Discharges in Capacitive Coupled Plasma Reactor

Br-based plasmas potentially provide selective etching of Si. The characteristics of homogenous discharge in mixed gases of HBr and He are investigated numerically based on a self-consistent 2D fluid model. The model takes into account the primary processes like excitation and ionization. The reactions of radicals with radicals, neutrals with neutrals and radicals and neutrals are taken into account in HBr/He discharge and therefore can adequately represent discharge plasma. Based on simulation results of the self-consistent 2D fluid model, the dominant species for Si etching in HBr/He plasma discharge are Br, Br⁺, H and HBr⁺. The impact of frequency, voltage, electrode gap, and gas mixture ratio on the densities of these important species in HBr/He has been explored. Simulation results indicate that elevating high frequency electrode’s frequency and voltage, enhances etching species densities. Increasing the electrode gap, the densities of all plasma species decrease and vice versa. The addition of He to HBr plasma decreases Br and HBr⁺ densities while increases Br⁺ density. Densities of active species for Si etching and subsequently chemical etching versus physical sputtering in HBr/He plasma can be controlled by tuning input parameters and the desired etching can be achieved.     

Production of a spin-polarized,metastable He(23 S) beam for studies in atomic and surface physics

This beam was developed as a target for a crossed-beam electron-atom scattering experiment on the interaction of a polarized spin-1/2 electron with a polarized spin-1 atom. In the future this beam will be used in “Spin-Polarized Metastable Atom Deexcitation Spectroscopy” (SPMDS) for studying ferromagnetic surfaces without and with adsorbate layers. We use a discharge source for producing a beam of metastable helium atoms, a permanent sextupole magnet with a central stop at its exit for selecting He(2³ S) atoms in the Zeeman substatem _s =+1, a zero-field spin flipper for reversing the atomic beam polarization with respect to a magnetic guiding field, and a Stern-Gerlach magnet for analyzing the atomic polarization. At a distance of 90 cm beyond the exit of the sextupole, in the “interaction region” of an experiment, the polarized beam has a circular cross section of about 6 mm FWHM and a particle density of 1 · 10⁷ atoms/cm³. The reversible spin polarization was determined asP=0.90±0.02. A possible contamination of the beam with metastable singlet atoms is included within this value; the ground-state He atoms are not considered to be part of the polarized beam. An observed contamination with long-lived Rydberg atoms can easily be destroyed by applying a high electric field.     

Ion kinetic energy distributions and their relationship to fundamental plasma parameters in a radio frequency glow discharge source

Studies are performed to evaluate the effect of discharge power, pressure, and sampling position on the kinetic energy of ions sampled from a radio frequency glow discharge (rf-GD) source. The average kinetic energy of ions decreases with increases in discharge power (20–40 W) and pressure (130–300 mTorr), with typical values lying in the range of 10–14 eV. Average ion kinetic energy (1KE) values increase at longer sampling distances from the cathode surface. The fundamental plasma parameters of positive ion number density (n_i) and plasma floating potential (V_f) are also measured via a Langmuir probe technique in order to investigate their relationships to the extracted ion beam characteristics. Total ion beam currents measured on a Faraday plate mounted behind the sampling cone reveal that the positive ion density and beam current track each other with respect to changes in discharge power and sampling position. The obtained IKE distributions are dominated by a broad, low energy peak extending from 0-to-20 eV with a high energy shoulder, which is indicative of rf modulation effects. Average IKEs track V_f as a function of power, pressure and sampling distance. The IKEs measured here are much lower than V_j (by −12 eV in most cases), suggesting that rf modulation effects and collisions in the anode sheath influence the observed energies.     

Time-resolved optical emission spectroscopic measurements of He plasma induced by a high-power CO2 pulsed laser

Laser-induced breakdown spectroscopy of helium plasma, initially at room temperature and pressures ranging from 12 to 101 kPa was investigated using a transverse excitation atmospheric CO₂ pulsed laser (λ = 9.621 and 10.591 μm, a full width at half maximum of 64 ns, and an intensity from 1.5 to 5.36 GW cm⁻²). The helium breakdown spectrum is mainly due to electronic relaxation of excited He, He⁺ and H. Plasma characteristics were examined in detail on the emission lines of He and He⁺ by the time-integrated and time-resolved optical emission spectroscopy technique. Optical breakdown threshold intensities, ionization degree and plasma temperatures were obtained. An auxiliary metal mesh target was used to analyze the temporal evolution of the species in the plasma. The results show a faster decay of the continuum emission and He⁺ species than in the case of neutral He atoms. The velocity and kinetic energy distributions for He and He⁺ species were obtained from time-of-flight measurements. Electron density in the laser-induced plasma was estimated from the analysis of spectral data at various times from the laser pulse incidence. Temporal evolution of electron density has been used for the estimation of the three-body electron-ion recombination rate constant.     

Kinetics and nature of the slow stage of cathodic hydrogen evolution on iron in aqueous and water-ethylene-glycol solutions of HCl in the presence of o-fluorophenylbiguanidine

The influence of the concentration of o-fluorophenylbiguanidine (FF) (0.5–40 mM) on the kinetics of hydrogen evolution on iron in aqueous and ethylene glycol (10 wt % H₂O) solutions with an electrolyte x M HCl + (1 ? x) M LiCl was studied. In aqueous media, the introduction of increasing concentrations of FF led to a transition from one slow stage to other stages in a series: slow discharge → slow recombination → slow lateral diffusion → slow discharge. In ethylene glycol media, the series is formally the same, but there is no initial slow discharge and hydrogen evolution (HER) in supporting solutions is limited by chemical recombination, which shifts to slow lateral diffusion already in the presence of 0.1 mM FF. In aqueous solutions, this change in the nature of the rate-limiting stage requires a 50-fold increase in the FF concentration. Finally, at a certain FF concentration, HER occurs under the conditions of slow discharge.     

Reactive scattering of a helium seeded oxygen atom beam

A high pressure microwave discharge source operating with a dilute mixture of O₂ in He has been used to produce a supersonic nozzle beam of O atoms seeded in He. This source has been used to study the reactive scattering of O atoms with Cl₂ and CS₂ molecules at an initial translational energy E = 38 kJ mol^?1. Velocity distribution of reactive scattering were measured over a wide angular range by cross-correlation time-of-flight analysis. The O + Cl₂ reaction proceeds via a short-lived collision complex while the O + CS₂ reaction follows a stripping mechanism.     

Stimulated CO emission of the (1 → 0) band in a pulse initiated (CS2 + O2) chemical laser

Chemi-excitation of CO^(v) to generate stimulated emission by v = 1 → 0 transitions has been achieved in CS₂ + O₂ + He mixtures, initiated by 13 kV pulses. The discharge is impressed axially along the laser tube. Rotational lines ranging from P(14) to P(10) have been observed. This partial inversion occurs only under strictly controlled conditions.     

Optical emission spectroscopy diagnostics of inductively-driven plasmas in argon gas at low pressures

An optical emission spectroscopy method for determination of electron temperature, electron density and gas temperature is developed and applied for diagnostics of inductively-driven argon discharges in a cylindrical geometry. The discharges are maintained at frequency 27 MHz, applied power varied in the limits P = (90 – 160) W and gas pressure in the range p = (1.1 – 117.3) Pa. The method combines measurements of emission spectral line intensities and profile broadenings with a collisional-radiative model of argon plasma at low pressure. The model is employed for investigation of the plasma kinetics governing the population densities of 3p⁵4s and 3p⁵4p argon configuration levels, treated separately. In the numerical calculations the electron density and electron temperature are varied whereas the values of the third plasma parameter — the gas temperature — are involved as obtained data from the experiments. Comparison of the experimental results of the line-intensity ratios with those calculated by the model yields the values of the electron density and temperature. The dependence of the electron temperature, electron density and gas temperature on the discharge conditions is obtained and discussed in the study.     

Evaluation of continuous hydride generation combined with helium and argon microwave induced plasmas using a surfatron for atomic emission spectrometric determination of arsenic,antimony and selenium

The direct coupling of continuous hydride generation with both Ar and He microwave induced plasmas (MIP) sustained in a surfatron has been optimized for the simultaneous determination of arsenic, antimony and selenium with atomic emission spectrometry. While a discharge tube of quartz was found suitable for the Ar plasma, the use of an Al₂O₃ tube led to improved performance of the He plasma. The He MIP was found to be less tolerant to the introduction of hydrogen than the Ar MIP, and correspondingly the hydride generation should be operated at a lower flow rate of 0.5% NaBH₄ solution. The introduction of the H₂O vapour produced during hydride generation into both discharges was found to greatly decrease the sensitivities and to degrade the measurement precision. It could be effectively removed with trapping by concentrated H₂SO₄. The detection limits (3σ) for As, Sb and Se are 1, 0.4 and 1 ng ml⁻¹ with the Ar MIP, and 2, 0.3 and 6 ng ml⁻¹ with the He MIP, respectively. The calibration curves are linear over three decades of concentration. The mutual interferences from As(III), Sb(III), Se(IV), Bi(III) and Sn(IV) were found to be negligible at interferent concentrations below 1 μg ml⁻¹ and in most cases the tolerable interferent concentrations are up to 20 μg ml⁻¹. The proposed method has been applied to the determination of As, Sb and Se in tea samples at μg g⁻¹ levels.     

Rotational 1 → 0 transitions in muonic helium-hydrogen molecular ions due to external Auger process

Rotational J = 1 → J = 0 transitions in (Heμh)_J muonic molecular ions (where He and h are helium and hydrogen isotopes, respectively), induced by external Auger process in collision with hydrogen isotope atoms are considered. The obtained reaction rates, normalized to liquid hydrogen density, range between 3.4 · 10¹¹ s^-1 and 11.2 · 10¹¹ s^-1 for different isotope combinations. Rotational state populations of Heμh in hydrogen isotope-helium mixtures are also calculated.     

Study of a new direct current atmospheric pressure glow discharge in helium

In this study a new DC-APGD operated in He was developed and characterized. The discharge is operated at 0.9 kV and about 25-35 mA and at a gas flow of 100 ml/min. The source was spectroscopically studied and parameters such as the rotational temperature (T_rot), the excitation temperature (T_exc), the ionization temperature (T_ion) and the electron number density (n_e) were determined. The current-voltage characteristic of the source was studied as well. At optimized conditions the discharge operates in the normal region of the current-voltage characteristic. Rotational and excitation temperatures determined with the use of OH band and Fe I lines as thermometric species were of the order of about 900-1200 and 4500-5500 K, respectively. This indicates that despite of the atmospheric pressure, the discharge is not in LTE. Spatially resolved temperature measurements were performed with axial as well as radial resolution and showed relatively flat profiles. Axially resolved emission intensity profiles for several species such as H, N₂, N₂⁺, OH, He and Hg were determined. It also was found that H₂ introduced into the He by electrolysis of acid solutions such as in ECHG considerably increases the spectroscopically measured gas temperatures but decreases the analyte line intensities, as shown for Hg.     

内嵌镧金属富勒烯的高产率合成及异构体比例调控

采用电弧放电法制备内嵌镧金属富勒烯的原灰,通过改变氦气压力及电流强度来提高内嵌镧金属富勒烯产率。原灰由1,2,4-三氯苯提取并回溶入甲苯后,利用分析型高相液相色谱(HPLC)对提取液中各富勒烯组分进行分析。通过分别衡量3种常见含镧金属富勒烯La@C2v-C82、La@Cs-C82和La_2@C_(80)与C84的相对峰面积比,探讨了氦气压力和电流强度等对3种金属富勒烯产率的影响。实验结果表明,氦气压力与电流强度共同决定了金属富勒烯的产率,在(1)低电流高氦气压、(2)中等电流中等氦气压、(3)高电流低氦气压的条件下都可以高产率地获得含镧金属富勒烯。此外,调整电流强度和氦气压力可以改变La@C2v-C82和La@Cs-C82的相对比例。例如,在电流为100、120 A或氦气压为20、35 k Pa时,此前认为的"minor"异构体La@Cs-C82的含量甚至高于"major"异构体La@C2v-C82。还发现降低电流强度或减小氦气压力可促进La_2@C_(80)的生成,这表明La_2@C_(80)与La@C82的形成过程可能是不同的。     

Semiclassical calculation of cross sections and rate constants for vibrational deactivation of HD (v = 1) colliding with 4He

A semiclassical collision model has been used to calculate the rate constant for vibrational relaxation in HD (v = 1, j = 0) colliding with ⁴He. The He + HD potential surface was obtained from an analytical He + H₂ surface previously used for similar calculations on He + H₂ and He + D₂. The theoretically calculated rate constant is about 50% below that experimentally determined in the temperature range 80–300 K.     

Ultrasensitive determination of mercury by solution anode glow discharge atomic emission spectrometry coupled with hydride generation

An innovative method for the ultrasensitive detection of mercury by solution anode glow discharge atomic emission spectroscopy (SAGD-AES) coupled with hydride generation (HG) was first investigated. In this method, the mercury vapor generated by the HG was transmitted to the SAGD through the miniature hollow tungsten tube for excitation and detected by a miniaturized spectrograph. A thorough parametric evaluation of the HG and SAGD system was performed, including the type and concentration of carrier acid, He flow rate, concentrations of NaBH₄, discharge current and discharge gap. Under optimal operating conditions, the detection limit for Hg²⁺ achieved 0.03 μg/L, with a relative standard deviation of 1.1% at the Hg²⁺ concentration of 5 μg/L. Moreover, the correlation coefficient of the calibration curve was 0.9996 in the range between 0.1 and 10 μg/L. The accuracy and practicability of HG-SAGD-AES were verified by measuring GBW09101b (human hair), GBW10029 (fish), soil and rice samples. The results showed good agreement with the certified values and values from direct mercury analyzer (DMA).     

Apparent molar and partial molar volumes of aqueous ceric ammonium nitrate solutions at 20, 25, 30, and 35°C

Present paper reports the measured densities (ρ) and refractive indices (n _D) of aqueous solutions of ceric ammonium nitrate (CAN) at 20, 25, 30, and 35°C in different concentrations of solution. Apparent molar volumes (φ_v) have been calculated from the density data at different temperatures and fitted to Massons relation to get limiting partial molar volumes (? _v ⁰ ) of CAN. Refractive index data were fitted to linear dependence over concentration of solutions and values of constant K and n _D ⁰ for different temperatures were evaluated. Specific refractions (R _D) of solutions were calculated from the refractive index and density data. Concentration and temperature effects on experimental and derived properties have been discussed in terms of structural interactions.