Matrix isolation study of the products of the interaction of electrons and of argon atoms in excited Rydberg states with HCCIF2

Infrared absorptions of the (CICF)?H—F^? and HCF^?₂ anions have been identified in the spectrum of the products of the photolysis of HCCIF₂ isolated in an argon matrix at 14 K using radiation in the 147—105 nm spectral range. These anions are also produced in matrix experiments in which the Ar:HCCIF₂ sample is codeposited with an atomic beam of sodium and charge transfer processes are induced by mercury are radiation, as well as in experiments in which the sample is codeposited with a beam of argon that has been passed through a microwave discharge. Both the spectral data and molecular orbital calculations for HCF^?₂ indicate that this molecule has an exceptionally weak CH bond and that its apex angle is considerably more acute than that of the uncharged HCF₂ radical. The high threshold for ion production from HCCIF₂ dictates consideration of the role played by highly excited Rydberg states of argon in the discharge experiments. It appears probable that charge transfer occurs between these excited argon and HCCIF₂. The high ion yield typical of the discharge experiments is also consistent with product formation resulting from collision of matrix-isolated HCCIF₂ with free excitons formed by the impact of highly excited argon atoms at the surface of the solid deposit.     

Monte Carlo Simulation of Radiation Trapping in Hg–Ar Fluorescent Discharge Lamps

The line spectra of emitted resonance radiation from mercury and the effective decay rates of the Hg 6³P₁ and 6¹P₁ levels in mercury–argon discharges are simulated by a Monte Carlo method. The hyperfine splitting, the natural isotopic composition, collisional transfer of excitation, foreign gas collisions and quenching are considered to describe in detail the 253.7 nm and 184.9 nm lines. The calculations are performed for Hg vapor densities corresponding to coldest spot temperatures of 5–100°C, and discharge parameters typical for fluorescent lamp operation. The densities of the Hg 6³P₁ and 6¹P₁ levels are consistently estimated by means of a set of balance equations for the Hg 6³P₀, 6³P₁, 6³P₂, and 6¹P₁ excited states. The resulting uv radiation output of the discharge is then estimated for a tube radius of 18 mm, argon pressure of 400 Pa, discharge current 0.4 A, and wall temperatures of 20–80°C. The results obtained show a good agreement as compared with published experimental data.     

Matrix isolation study of the products of the interaction of electrons and metastable argon atoms with HCCl2F

Two groups of infrared absorptions common to experiments in which samples of HCCl₂ isolated in an argon matrix at 14 K are exposed to vacuum ultraviolet radiation or to electrons produced by ultraviolet irradiation of an alkali metal, as well as to experiments in which the Ar:HCCl₂F sample is codeposited with a beam of argon atoms excited in a microwave discharge, have been assigned to anions produced upon associative and dissociative electron capture by HCCI₂F. Detailed isotopic substitution studies suggest that these anions are (Cl₂C)H?F^?, representing a unique type of hydrogen bonding, and HCCIF^?. The HCClF^? anion photodecomposes in the 345–250nm spectral region, but the products of its photodecomposition have not been identified. Both CCl₂ and Cl₂CF are also produced in the discharge experiments, but there is no evidence for the production of HCF. Mechanisms for the formation of ion products by electron capture and by exposure of HCCl₂F to radiation or to excited argon atoms of energy equal to or less than 11.8 eV are considered.     

Some spatial effects observed in the axially viewed filament argon microwave induced plasma with solution nebulization

Spatial profiles of analyte emission in an axially viewed argon filament microwave induced plasma sustained in the TE₁₀₁ rectangular cavity have been measured along a discharge tube cross-section for neutral atoms as well as ion lines of several elements. The filament diameter was approximately 1 mm. The analyte solution was introduced by means of an ultrasonic nebulizer without desolvation. The radial emission distribution depends on the operating parameters and is different for each of the analytes examined. Spatial distributions of excitation temperature (4000–6000 K) measured with Ar I lines by the Boltzmann plot method as well as electron temperature (6000–8000 K) by line to continuum emission ratio measurements at Ar I 430 nm and electron number density (1–1.5×10¹⁵ cm⁻³) by the Stark broadening method of the H_β line were determined to support the evidence of plasma processes. In the presence of excess sodium the enhancement of emission intensity and its shift to the plasma center appears to be the result of increased analyte penetration to the plasma. Changes in spatial emission profiles for Ca atoms and ions suggest that for this element ambipolar diffusion may be important as an additional interference mechanism. A possibility of minimizing spectral interferences from argon emission lines by choosing an off-axis plasma region for emission intensity measurements is indicated.     

Tetraf luoromethane Injected into a dc Argon Glow Discharge

Low partial pressures (10^?5 to 10^?3 Torr) of tetrafluoro-methane have been injected into a dc argon glow discharge (85 × 10^?3 Torr, 1000 V) and the discharge-induced removal rate of the CF₄ molecules from the vapor phase has been studied with a mass spectrometer as a function of the discharge current and the CF₄ concentration. The ultimate disposition of the CF₄ is believed to be in the form of polymeric deposit on the walls of the discharge vessel. The removal rate of CF₄ is proportional to the discharge current and also proportional to the concentration of CF₄in the low concentration regime. At higher partial pressures of CF₄ (～1 × 10^?3 Torr) the removal rate tends to saturate, becoming independent of the CF₄ concentration.     

Ion formation processes in the afterpeak time regime of pulsed glow discharge plasmas

The formation of ions following the termination of power in a pulsed glow discharge ion source is investigated. The populations of ionized species containing sputtered atoms M⁺, M ₂ ¹ :, and MAr⁺ are observed to maximize after the termination of discharge power. Collisions involving sputtered atoms and metastable argon atoms, Penning and associative ionization, are considered to be responsible for the formation of ions in the discharge afterpeak time regime. The domination of these ion formation processes during the afterpeak time regime is supported by the results from investigations of discharge operating parameters, metastable argon atom quenching, and ion kinetic energy distributions.     

Plasma diagnostics of barrier-torch discharge in argon flow in a capillary by cross-correlation spectroscopy

The radiation kinetics of the plasma of barrier-torch disrcharge in argon flow in a capillary has been studied by cross-correlation spectroscopy. It was established that the discharge emission spectrum consists of peaks of electronically excited states of argon, bands of hydroxyl radicals, and a second positive system of nitrogen. An analysis of the spatio-temporal distributions of emission intensity for the selected spectral indicators showed that the causes of the torch are ionization waves that extend through the capillary from the electrode system with a speed of 10⁵ m/s and project up to 3–4 mm. It was established that the formation of electronically excited molecules of nitrogen N₂(C ³Π _u ) in the torch of discharge occurs mainly on the reaction between metastable electronically excited atoms of argon and molecules of nitrogen in the electronic ground state.     

The Effects of Gas Composition on Active Species and Byproducts Formation in Gas–Water Gliding Arc Discharge

The effects of gas composition on hybrid gas–water gliding arc discharge plasma reactor have been studied. The voltage cycles are characterized by a moderate increase in the tension which is represented by a peak followed by an abrupt decrease and a current peak in the half period (10 ms). Emission spectrum measurements revealed that ^•OH hydroxyl radicals are present in the discharge with feeding any gas. The H₂O₂ concentrations reach 38.0, 15.0, 10.0, and 8.0 mg/l after 25 min plasma treatment with oxygen, argon, air, and nitrogen, respectively. O₃ was produced when oxygen and air are used, but not when nitrogen and argon. The O₃ concentration reached the highest value 1.0 mg/l after 25 min plasma treatment with oxygen feeding gas, but gradually decreased to 0.2 mg/l after that. With feeding nitrogenous gas, NO₂ ⁻ and NO₃ ⁻ byproducts were formed by the plasma chemical process.     

A spectrometric study of a 40 MHz inductively coupled plasma—VI: Argon continuum in the visible region of the spectrum

The nature of a pure Ar continuum observed in ICP-AES has been studied in the 400–700 nm range. The radiative recombination is predominant below 500 nm, but bremsstrahlung must be considered above 500 nm. The electron temperature T_e deduced from the ratio of an Ar line to the adjacent continuum is about 10,000 K, which is significantly different from the excitation temperatures previously measured in this source. The electron number density (n_e) determined from the continuum is in good agreement with the value determined from the Stark effect on Ar 1549.5 nm line and about 5 × 10²⁰ m^?3. The continuum varies with the input power and the carrier gas flow rate. This is mainly due to the variation of n_e.     

Energy transfer in collisions of excited Ar(3P0.2) metastable atoms with H(2S) atoms. II. Lyman-α emission profile

Spectra of the Lyman-α emission resulting from the Ar(4s, ³P_2.0) + H(Is, ²S) interaction have been recorded. The emission line profile is essentially rectangular with a full width of 13 pm. These results show that excited H(n = 2) atoms are formed in the reaction, with nearly all the excess energy (1.34 eV) appearing as kinetic energy of the hydrogen atom. Lyman-α emission profiles also have been obtained from microwave discharge plasmas in argon and helium, containing traces of hydrogen; these profiles are compared with those from the Ar(³P_2.0) + H(²S) system.     

Gas and liquid phases interaction at the FeO·Cr2O3 cathode of a direct-current arc discharge

The study of an arc discharge in argon has been made with the cathode of the discharge system in the form of molten chromite, FeO·Cr₂O₃. The partial pressure distributions of the elements Fe and Cr, as well as the temperature distributions, have been determined in the arc by spectroscopic methods. The data obtained were used, in conjunction with a mathematical model, for the determination of the oxygen species distribution in the same medium. The cathode bath surface was measured by means of the two-wavelength method. From a consideration of free energy of reaction values, it is concluded that the presence of elemental Fe and Cr in the cathode bath is mainly related to the migration of Fe⁺ and Cr⁺, present in the arc, toward the liquid cathode. The formation of these elements in the molten cathode is very unlikely.     

Comparison of temperature measurements in ICP and MIP with Ar and He as plasma gas

Various temperature measurements have been carried out in microwave induced plasmas (MIP) generated with a surfatron and inductivcly coupled plasmas (ICP) both with argon and helium as plasma gas. Iron has been used for the determination of excitation temperature, and OH and N⁺₂ for rotational temperatures. In the case of the Ar ICP, equilibrium is attained between the various temperatures (4500 K), as previously described. On the other hand, in the He ICP and the MIPs, iron provides the highest temperature (4500 K) but discrepancies are obtained with results from N⁺₂ and OH. These two species show lower values, especially OH (2000 K).     

Vertically positioned axially viewed aerosol cooled plasma — a new design approach for microwave induced plasma optical spectrometry with solution nebulization

A vertically positioned axially viewed argon microwave induced plasma (Ar-MIP) system is described, which can serve as a spectrochemical excitation source. The design concept of improved TE₁₀₁ rectangular cavity based on strong coupling between the plasma load and the magnetron generator has been presented. The idea of plasma cooling with a pure water aerosol is explained. The torch cooling system which permits aerosol generation and circulation has been described in detail. The influence of cooling on the argon plasma positioning in the discharge tube was investigated. The spectroscopic temperatures of iron and argon have been measured to evaluate excitation conditions and effect of plasma cooling. Analytical performance of the presented MIP system was characterized by determination of the limits of detection for some elements and comparison with other Ar-MIP experimental setups. Analysis of certified reference material was performed to determine the accuracy and precision available with the presented system.     

H2/Ar direct current glow discharge mass spectrometry at constant voltage and pressure

The addition of hydrogen to a direct current (dc) - argon glow discharge (GD) coupled to a time of flight mass spectrometer has been studied using a fixed voltage between the electrodes and a fixed discharge pressure. Hydrogen contents investigated were 0.5%, 1% and 10% v/v in the argon discharge and the samples under study consisted of a copper-base, a nickel-base and an iron-base homogeneous materials. Also, the in-depth profile analysis of a tin plate was investigated. Results have shown that hydrogen addition gives rise to significant changes in the slope of the linear relationship between the electrical current and the discharge voltage. Clearly, the electrical resistance of the discharge at the typical operation voltages in the interval 600–1000 V increases with hydrogen added to pure argon.A decrease of the sputtering rates was observed the higher the hydrogen concentrations. Besides, the “reduced sputtering rates”, i.e. the sputtering rates divided by the corresponding electrical current, were also lower for the H₂/Ar discharges than for pure argon. However, the analytical ion signals observed using discharge voltages higher than 900 V turned out to be higher in a 0.5% H₂/Ar discharge than in pure argon for the copper and nickel materials. Besides, for the three samples investigated the ion yields were from 1.5 up to 3 times higher in 0.5% H₂/Ar discharges as compared to the pure argon.Finally, the effect of 0.5% H₂ addition to the Ar discharge on the in-depth profile of a tin plate has also been investigated. As compared to the use of a pure Ar GD, higher sensitivity for major and minor components of the coating were observed without loss of the relative depth resolution achieved.     

Comparison in the analytical performance between krypton and argon glow discharge plasmas as the excitation source for atomic emission spectrometry

The emission characteristics of ionic lines of nickel, cobalt, and vanadium were investigated when argon or krypton was employed as the plasma gas in glow discharge optical emission spectrometry. A dc Grimm-style lamp was employed as the excitation source. Detection limits of the ionic lines in each iron-matrix alloy sample were compared between the krypton and the argon plasmas. Particular intense ionic lines were observed in the emission spectra as a function of the discharge gas (krypton or argon), such as the Co II 258.033 nm for krypton and the Co II 231.707 nm for argon. The explanation for this is that collisions with the plasma gases dominantly populate particular excited levels of cobalt ion, which can receive the internal energy from each gas ion selectively, for example, the 3d⁷4p ³G₅ (6.0201 eV) for krypton and the 3d⁷4p ³G₄ (8.0779 eV) for argon. In the determination of nickel as well as cobalt in iron-matrix samples, more sensitive ionic lines could be found in the krypton plasma rather than the argon plasma. Detection limits in the krypton plasma were 0.0039 mass% Ni for the Ni II 230.299-nm line and 0.002 mass% Co for the Co II 258.033-nm line. However, in the determination of vanadium, the argon plasma had better analytical performance, giving a detection limit of 0.0023 mass% V for the V II 309.310-nm line.     

Effect of LiPF<Subscript>6</Subscript> on the thermal behaviors of four organic solvents for lithium ion batteries

The thermal behaviors of four organic solvents with/without LiPF₆ were measured by C80 microcalorimeter at a 0.2°C min⁻¹ heating rate. With the addition of 1 M LiPF₆, the ethylene carbonate (EC) and propylene carbonate (PC) show the exothermic peaks at elevated temperature, which lessen their stabilities. The exothermic peak temperatures of EC and PC based LiPF₆ solutions are at 212 and 223°C, respectively, in argon filled vessel. However, two endothermic peak temperatures were detected in diethyl carbonate (DEC) based LiPF₆ solution at 182 and 252.5°C, respectively, in argon filled vessel. Dimethyl carbonate (DMC) based LiPF₆ solution shows two endothermic peak temperatures at 68.5 and 187°C in argon filled vessel at elevated temperature. Consequently, it is concluded that LiPF₆ play a key role in the thermal behavior of its organic solution.     

Benzene B2u → A1g emission in an argon afterglow

The benzene ¹B_2u → ¹A_1g emission spectrum is observed in a flowing argon afterglow by a low power microwave discharge. No emission of dissociation products was found in 2000–7000 Å region.     

Ir matrix isolation spectra of some perfluoro organic free radicals. Part III. n-C3F7 and iso-C3F7

The perfluoro radicals n-C₃F₇ and iso-C₃F₇ have been prepared by pyrolyzing the corresponding iodides in a platinum effusion tube at temperatures between 450–550°C and isolated in argon matrices. By eliminating absorption bands attributed to known fluorine compounds and applying relative absorption band intensity correlations, several absorption bands have been assigned, some 30 to n-C₃F₇ and 29 to iso-C₃Fe₇, in the spectral range 2000–200 cm^-1. A tentative vibrational assignment is presented for both species on the assumption of C_s symmetry. Some thermodynamic implications of the findings are also discussed.     

Distribution of metastable argon atoms in the modified Grimm-type electrical discharge

The absorbance by metastable argon atoms of the Ar 696.543 nm line in the modified Grimm-type electrical discharge source was measured at different discharge conditions and at distances varying from 0.25 to 6 mm from the cathode. A uranium/argon hollow cathode lamp was used as primary source, which gave an argon gas temperature of 850 K when run at 12 mA. A maximum absorbance of 0.57 was found 3 mm from the cathode at 600 V, 80 mA. The magnitude of absorbance increases with discharge current while the position of maximum absorbance shifts away from the cathode with increase in discharge voltage. The quenching of metastable atoms by nitrogen is demonstrated.The spatial distribution of the intensity of four different types of spectral lines is shown. The approximate number densities of the different particles are 10¹²cm^?3 for metastable argon atoms, 10¹⁶cm^?3 for neutral argon atoms, 10¹³ cm^?3 for sputtered copper atoms and 10¹⁴cm^?3for electrons.     

Investigation of the afterglow time regime in pulsed radiofrequency glow discharge time‐of‐flight mass spectrometry

The pulsed power operation mode of a radiofrequency (rf) glow discharge time‐of‐flight mass spectrometer was investigated, for several ions, in terms of intensity profiles along each pulse period. Particular attention was paid to the plateau and transient afterglow regions. An rf pulse period of 4 ms and a duty cycle of 50% was selected to evaluate the influence of discharge parameters in the afterglow delay and shape of Ar⁺, Ar₂⁺ and several analytes (Br, Cl, Cu) contained in polymeric layers. Pulse shapes of Ar⁺ and Ar₂⁺ ions vary with pressure and power. At low pressures the highest intensity is observed in the plateau while at higher pressures (>600 Pa) the afterpeak is the dominant region. Although the influence of the applied power is less noticeable, a widening of the afterglow time regime occurs for Ar⁺ when increasing the power. Maximum intensity of the argon signal is measured in the afterglow at 30 W, while the area of such afterpeak increases with power. The maximum intensity of Ar₂⁺ is obtained at the highest power employed (60 W) and the ratio maximum intensity/afterglow area remains approximately constant with power. Analytes with ionization potentials below (Cu) or just above (Br) the argon metastable energy show maxima intensities after argon ions decay, indicating they could be ionized by collisions with metastable Ar atoms. Chlorine signals are observed in the afterglow despite their ionization potential is well above the energy of argon metastable levels. Moreover, they follow a similar pattern to that observed for Ar₂⁺, indicating that charge‐transfer process with Ar₂⁺ could play a significant role. Copyright © 2011 John Wiley & Sons, Ltd.