Electron Detachment Reactions Research Articles

Determining the swarm parameters of gases considering ion kinetics by parallel genetic algorithm on GPU platform

In this work, a convenient and efficient method is proposed to determine swarm parameters considering ion kinetics from pulsed Townsend (PT) measurements. First, a physical model was presented to describe the development of PT discharge considering electron detachment and ion conversion reactions. A numerical solution to the model was also proposed. In order to assess the precision of our calculations, we presented the calculated electronic and ionic transients derived from our model for different cases. Then, a genetic algorithm (GA) was proposed to find a set of swarm parameters, under which the deviation between the simulated current waveform and the actual measured current waveform is minimum. It is time-consuming to simulate a single waveform, and since a large number of waveforms need to be simulated in the GA, graphic processing unit-based parallel computing is used to improve computing efficiency. Finally, the swarm parameters of dry air considering electron detachment and ion conversion processes using the method were obtained and they are in good agreement with those in references.

Double-pulse streamer simulations for varying interpulse times in air

In this paper, we study how streamer discharges are influenced by a previous voltage pulse using an axisymmetric fluid model. We simulate double-pulse positive streamers in N2–O2 mixtures containing 20% and 10% O2 at 1 bar. By varying the time between the pulses between 5 ns and 10 µs, we observe three regimes during the second pulse: streamer continuation, inhibited growth and streamer repetition. In the streamer continuation regime, a new streamer emerges from the tip of the previous one. In the inhibited regime, the previous channel is partially re-ionized, but there is considerably less field enhancement and almost no light emission. Finally, for the longest interpulse times, a new streamer forms that is similar to the first one. The remaining electron densities at which we observe streamer continuation agree with earlier experimental work. We introduce an estimate which relates streamer continuation to the dielectric relaxation time, the background field and the pulse duration. Furthermore, we show that for interpulse times above 100 ns several electron detachment reactions significantly slow down the decay of the electron density.

Ion fluxes and memory effects in an Ar–O2 modulated radiofrequency-driven atmospheric pressure plasma jet

In this work we used molecular beam mass spectrometry to characterize ion fluxes produced by a modulated radiofrequency (RF)-driven atmospheric pressure plasma jet operating in a homogeneous gas environment (Ar + 1% O2). The influence of the RF modulation frequency (100 Hz to 20 kHz) on the ion fluxes was investigated by time-resolved measurements, and the lifetimes of the dominant ions, O2 +, NO+, O−, O2 − and O3 −, were found to be 28 ± 2, 117 ± 8, 7.3 ± 0.4, 17 ± 1 and 23 ± 2 μs, respectively. The absolute ion densities in the near afterglow region were found to be of the order of 1011 cm−3. Significant differences in the dynamics of the positive and negative ions were found; these are explained by the presence of electrons at similar densities in the afterglow produced by electron detachment reactions from negative ions due to the large concentrations of atomic oxygen and singlet delta oxygen. Transitions in ion flux dynamics for different modulation frequencies and at the startup of the plasma were analyzed together with intensified charge coupled device images recording the plasma propagation in order to assess the dynamics of plasma plume propagation and how it is impacted by ‘memory effects’. Quantitative measurements of the ion densities enabling these memory effects are reported. The results in this paper highlight the tremendous impact of memory effects on plasma propagation and the corresponding pre-ionization.

Photochemistry of potassium ferrocyanide and its reaction with uridine 5′-monophosphate in aqueous solution under ultraviolet irradiation

The photochemical reaction of potassium ferrocyanide (K4Fe(CN)6) exhibits excitation wavelength dependence and non-Kasha rule behavior. In this study, the excited-state dynamics of K4Fe(CN)6 were studied by transient absorption spectroscopy. Excited state electron detachment (ESED) and photoaquation reactions were clarified by comparing the results of 260, 320, 340, and 350 nm excitations. ESED is the path to generate a hydrated electron (eaq−). ESED energy barrier varies with the excited state, and it occurs even at the first singlet excited state (1T1g). The 1T1g state shows ∼0.2 ps lifetime and converts into triplet [Fe(CN)6]4− by intersystem crossing. Subsequently, 3[Fe(CN)5]3− appears after one CN− ligand is ejected. In sequence, H2O attacks [Fe(CN)5]3− to generate [Fe(CN)5H2O]3− with a time constant of approximately 20 ps. The 1T1g state and eaq− exhibit strong reducing power. The addition of uridine 5′-monophosphate (UMP) to the K4Fe(CN)6 solution decrease the yield of eaq− and reduce the lifetimes of the eaq− and 1T1g state. The obtained reaction rate constant of 1T1g state and UMP is 1.7×1014 (mol/L)−1·s−1, and the eaq− attachment to UMP is ∼8×109 (mol/L)−1·s−1. Our results indicate that the reductive damage of K4Fe(CN)6 solution to nucleic acids under ultraviolet irradiation cannot be neglected.

Experimental observation of the effect of electron attachment and detachment reactions on the electron energy distribution in an inductive oxygen discharge

Electron energy distribution functions (EEDFs) are measured with varying radio-frequency (RF) power in an oxygen inductive discharge. At a pressure of 10 mTorr, the EEDF has a Maxwellian distribution, and the low-energy (1–5 eV) electron temperature, Te,low, monotonically decreases with RF power. However, at a pressure of 100 mTorr, Te,low increases at low RF power (80–150 W) and decreases at high RF power (150–300 W), and the EEDF has a Druyvesteyn-like distribution. These changes in Te,low are attributed to electron attachment and detachment reactions, which are the main creation and loss reactions of negative ions. To investigate this relationship between Te,low and collisional reactions, the reaction coefficients of several reactions are calculated, and the electronegativity (α) is measured with varying RF power. The EEDF is modified by electron attachment and detachment reactions, which lead to a change in Te,low; this modification of EEDF is supported by calculated reaction coefficients and measured α.

Modeling of streamer-to-spark transitions in the first pulse and the post discharge stage

The streamer-to-spark transition in a point-to-plane configuration in atmospheric pressure air is studied using a 2D–0D combined approach. A validated fluid code is used and improved to model the spark stage. 2D modeling of discharges at three different temperatures, 300, 600 and 800 K, are conducted; the spark transition occurs when the temperature reaches 800 K in the first pulse. A conservative criteria of spark transition temperature is proposed based on analytical solution and compared with experiments. Kinetics modeling of the post discharge stage is conducted with consistent input values extracted from the 2D model. Results show that the streamer-to-spark transition can be initiated at a lower temperature (600 K) and lower field (50–75 Td), and the long-lifetime O-atoms formed in previous pulses play an important role in ‘knocking off’ the electrons from negative charged species and maintaining the electron density in the post discharge stage. The dominating processes for electron production are electron detachment reactions from , and O−. The ionizations from excited species only accelerate the production of electrons when the plasma is already dense.

One-dimensional simulation of hydrogen production kinetic models by water vapor plasmolysis in a DBD plate reactor

The results of one-dimensional time-dependent simulation modeling of hydrogen production from water vapor dissociation using non-thermal discharge plasma in a plate-type reactor were developed. Three different water vapor dissociation reaction mechanisms pathway models were simulated at a water vapor temperature of 573 K and same boundary conditions. The electron collision cross sections of electron water vapor were utilized based on the reaction mechanisms. The electron attachment and detachment processes were described in detail; additionally, the surface charge accumulation, recombination of charged species, positive and negative ions production and losses are considered. The electron density, electric field, electric potential, electron temperature and the hydrogen mass fraction are presented across the plasma discharge gap and over time. The first model was described as direct water vapor decomposition into their constituent’s elements hydrogen and oxygen molecules. It was revealed that the formed hydrogen molecules increased across the plasma discharge gap over time. In model II, the simulation reaction mechanisms pathway included products of H2O+, OH+, and O+ ions. It was found a significant change in the electric potential and electric field across the discharge gap due to the charged species inside the plasma gap. In model III, it was introduced H− radicals which controlled H atoms production by the electron detachment reaction. The most interesting results of these simulation models were the growing of hydrogen molecules across the plasma gap over time. Further, it was observed that the produced hydrogen mass fraction from model III was higher than model II and model I.

Deep K-band Observations of TMC-1 with the Green Bank Telescope: Detection of HC7O, Nondetection of HC11N, and a Search for New Organic Molecules

Abstract The 100 m Robert C. Byrd Green Bank Telescope K-band (KFPA) receiver was used to perform a high-sensitivity search for rotational emission lines from complex organic molecules in the cold interstellar medium toward TMC-1 (cyanopolyyne peak), focussing on the identification of new carbon-chain-bearing species as well as molecules of possible prebiotic relevance. We report a detection of the carbon-chain oxide species HC7O and derive a column density of cm−2. This species is theorized to form as a result of associative electron detachment reactions between oxygen atoms and C7H−, and/or reaction of C6H2 + with CO (followed by dissociative electron recombination). Upper limits are given for the related HC6O, C6O, and C7O molecules. In addition, we obtained the first detections of emission from individual 13C isotopologues of HC7N, and derive abundance ratios HC7N/HCCC13CCCCN = 110 ± 16 and HC7N/HCCCC13CCCN = 96 ± 11, indicative of significant 13C depletion in this species relative to the local interstellar elemental 12C/13C ratio of 60–70. The observed spectral region covered two transitions of HC11N, but emission from this species was not detected, and the corresponding column density upper limit is (at 95% confidence). This is significantly lower than the value of previously claimed by Bell et al. and confirms the recent nondetection of HC11N in TMC-1 by Loomis et al. Upper limits were also obtained for the column densities of malononitrile and the nitrogen heterocycles quinoline, isoquinoline, and pyrimidine.

The kinetics of energetic O− ions in discharge H2O plasma

Using Monte Carlo simulation, the translational relaxation of energetic O− ions produced by dissociative electron attachment to molecules was studied in water vapor plasmas in a strong electric field. Initial O− ions are energetic and are more reactive than the ions being in equilibrium with the electric field. Because of this, the energetic O− ions have a chance to be involved in endothermic reactions prior to energy relaxation of these ions. The probabilities of charge exchange and electron detachment in ion-molecule interactions were calculated versus the reduced electric field. It was shown that several percent of energetic O− ions produced in water vapor plasma by dissociative electron attachment to H2O molecules are rapidly transformed to OH− ions due to charge exchange collisions or are decomposed to release free electrons. The total probability of charge exchange and electron detachment from energetic O− ions increases up to around 90% when these ions are produced by dissociative electron attachment to O2 molecules if oxygen is added to water vapour. This means that, in this case, most of energetic ions formed from O2 molecules are involved in charge exchange and electron detachment reactions prior to their thermalization.

ScF 2+ and ScHe 3+: two highly-charged episodes from the gas-phase adventures of scandium

Quantum chemical calculations on the thermochemistry of gas-phase ScF 2+ and ScHe 3+ are reported. As the lightest possible closed-shell combinations of a transition metal with a halogen or rare gas atom, the identified species each possess noteworthy attributes. Our calculations show that ScF 2+ is thermodynamically stable; its dissociation to either Sc 2+ + F or Sc + + F + is highly endothermic. Further, ScF 2+ is a plausible exothermic product of a yet-unknown class of electron-detachment reactions which can be described as associative charge doubling: viz., F + + Sc → ScF 2+ + e. The triply-charged species ScHe 3+ appears to be the lightest known thermodynamically stable molecular trication.

Direct Measurement of the Thermal Rate Coefficient for Electron Attachment to Ozone in the Gas Phase, 300–550 K: Implications for the Ionosphere

Attachment of thermal electrons to O3 was studied in 133 Pa He between 300-550 K; the process is extremely inefficient. The rate coefficient increases sharply with temperature from 0.9 to 5 x 10(-11) cm(3) s(-1) (+/-30%) and comparison to kinetic energy measurements suggests internal energy can drive the reaction. These determinations account for competing processes of diffusion, recombination, and electron detachment reactions, and imply that no significant zero-energy resonance cross section exists, contradicting recent electron-beam results that call for substantial revision of ionospheric models.

Electron Transport across Magnetic Filter in Negative Hydrogen Ion Source

Profiles of electron temperature and number density in a negative-ion source are investigated theoretically. Spatial dependence over the magnetic filter region is obtained using the equations of electron flux and electron heat flux that include the effect of interference of forces by the density gradient and temperature gradient. Due to the effect of the magnetic filter, temperature and density of the electron decrease from the source chamber to the extraction chamber, and the decrease depends on the magnitude of the magnetic flux. The effect of the magnetic filter on the production and destruction rates of the negative hydrogen ion is examined. The reaction rate for the dissociative attachment reaction which produces the negative hydrogen ion increases with the decrease of the electron temperature. However, the production rate per one vibrationally excited hydrogen molecule decreases with the decrease of electron density. On the other hand, the destruction probability of the negative ion by the electron detachment reaction decreases significantly by the decrease of the electron density and temperature. The magnetic filter does not enhance the production of the negative hydrogen ion, but it reduces the destruction of the negative ion because of the decrease of the electron density.

Pulsed technique for observing infrared emissions from ionic gas phase reactions at low reactant ion concentrations

A technique has been developed to detect infrared emissions from the products of ionic reactions in plasmas. The technique employs dual-phase digital lock-in amplification and cold filtering to permit the detection of the weak infrared chemiluminescence (IRCL) with a solid-state detector. A novel method of cleanly modulating plasma chemiluminescence by the pulsed introduction of reagent gases has been developed and implemented. This new technique has been tested by studying the well-characterized H-atom reactions, H+Cl2→HCl(v=0–4)+Cl and H+NO2→OH(v=0–3)+NO. Rotational and vibrational distributions have been measured for these two reactions and are presented and compared with previous determinations. Additionally, the associative electron detachment reaction, H+Cl−→HCl(v=0–2)+e, has been studied, demonstrating that IRCL can be collected from reactions occurring at a low number density approaching that of the plasma ionization (∼4×1010 cm−3). The resolution, and hence, the information content of the collected emissions from this reaction have been greatly improved over previous work, with which our data are compared.

Effect of buffer gas alterations on the thermal electron attachment and detachment reactions of azulene by pulsed high pressure mass spectrometry

A principal motivation for the present study is to determine the ion source conditions required for achievement of the high pressure limit (HPL) of kinetic behavior for the resonance electron capture (REC) reaction of azulene (Az), Az + e → Az −. This goal is accomplished here by measuring rate constants for the reverse process, thermal electron detachment by molecular anions of azulene, Az − → Az + e, by pulsed high pressure mass spectrometry by using a variety of buffer gases, methane, argon, nitrogen, and helium, over a range of pressures, from 1 to 6 Torr, over a range of temperatures, from 150 to 200 °C. From these measurements, it is shown that the ion source conditions commonly used in electron capture mass spectrometry for the trace analysis of REC-active molecules would not be sufficient for achievement of the HPL of the REC reaction of azulene and, therefore, would likely result in significantly reduced sensitivity to this compound. The problem highlighted here for the case of azulene is undoubtedly shared by many other REC-active compounds. The resolution of this problem is expected to require accommodation of several relevant factors shown here to be important in the case of azulene, including the choice of buffer gas, pressure, and ion source temperature.

Thermal electron detachment of the molecular anion of azulene at elevated pressures by ion mobility spectrometry

Rate constants, k TED, and their temperature and pressure dependence for the thermal electron detachment (TED) reaction of the molecular anion of azulene (Az − → Az + e) have been determined by ion mobility spectrometry (IMS). By this method, Az − ions are periodically introduced to a drift tube containing nitrogen gas at pressures ranging from 300 to 1100 Torr and temperatures ranging from 75 to 175 °C. During the time required for an Az − ion packet to drift to a Faraday detection plate, either a portion (at lower temperatures) or essentially all (at higher temperatures) of the Az − ions undergo TED. From the TED-modified IMS waveforms thereby produced, the magnitudes of k TED values have been deduced and compared with previous measurements of k TED for Az − made in buffer gases of much lower and higher pressures. The present results support a trend noted in the prior studies that the rate of TED by Az − is decreased by large increases in pressure to the near-atmospheric pressure range. A potential explanation of this unexpected effect of a buffer gas that is normally considered to be chemically inert is that a weak chemical interaction exists between the Az − ion and the nitrogen buffer gas molecules and this provides increased stability to the Az − ion under conditions of very high pressure and thereby increases the activation barrier of the TED reaction.

Coupled-channel calculations with Cartesian Gaussian basis functions for - collisions

The four-electron system - is treated in the semiclassical approximation. The nuclei are described classically as moving on straight-line trajectories and the electrons quantum mechanically by solving the time-dependent coupled-channel equations. As physical basis states we use completely antisymmetrized wavefunctions built from products of states with proper translation factors. In order to calculate the matrix elements of the electron-electron interaction analytically as far as possible, we expand the wavefunctions into Cartesian Gaussian basis functions. We present cross sections for electron detachment and mutual ionization reactions in the energy range -100 keV and compare them with experimental data.

High-frequency electrical breakdown in electronegative gases with fast electron attachment and detachment processes

Department of Physical Mechanics, Moscow Institute of Physics and Technology, 141700, Dolgoprudny, Russia Troitsk Institute for Innovation and Fusion Research, 142092 Troitsk, Moscow Region, Russia Received 1 April 1996 :Breakdown in a high-frequency uniform electric field in electronegative gases with fast electron attachment and detachment processes is theoretically studied. A process of electron pseudo diffusion introduced earlier by Aints et al is analysed, and a breakdown criterion is regularly derived using the great difference in rate scales for collisional processes. The criterion is generalized to account for an arbitrary number of negative ion species including those which are not involved in electron detachment reactions. The importance of the electron pseudo diffusion is illustrated for specified gases (air, , etc). It is argued that the application of the concept of pseudo diffusion to the breakdown in air under the conditions of the experiment conducted previously by Aints et al is invalid.

Electron-transfer reactions with buckminsterfullerene, C60, in the gas phase

Abstract The fundamental process of electron transfer is viewed from the new perspective provided by recent gas-phase measurements of reactions that remove electrons from the C60 molecule or donate electrons to singly and multiply charged C60 cations. Experimental results are reviewed for the chemical ionization of C60 by Penning ionization with metastable rare-gas atoms, single-electron transfer to atomic or molecular ions, double ionization by electron transfer, electron detachment reactions with He·+ or Ne·+, and multiple ionization by multiple-electron transfer to multiply charged rare-gas cations. Also, experimental results are reviewed for single-electron transfer to C·+ 60 and C2+ 60; a model previously proposed for the potential energy profile of single-electron transfer to C2+ 60 is included which argues in favour of a reaction barrier arising from the Coulombic repulsion between the single charged product ions of such a process. Results of measurements previously reported for single and double-electron transfer reactions with C·3+ 60 are also summarized. The latter reactions are unprecedented in electron transfer research. Data for thermal electron transfer reactions with Cn+ 60 (n4) are not available, but results are indicated for electron transfer from Cs to C4+ 60 at high collision energies. Intramolecular electron transfer is briefly discussed for exohedral and endohedral cation adducts of metal atoms and C60, and of exohedral adducts of molecules and C2+ 60. Finally, the occurrence of electron transfer involving C60 anions is briefly considered.

ChemInform Abstract: Electron Detachment Reactions of Fluorinated Carbanions with Atomic Hydrogen

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

Electron detachment reactions of fluorinated carbanions with atomic hydrogen

Rate constants were measured for electron detachment reactions of atomic hydrogen with CF−3, C2F−5, and C3F−3. The experiments were performed using a selected ion flow tube (SIFT) instrument. The density of atomic hydrogen was calibrated by studying the reaction of F− with H, and rate constants were measured relative to the known rate constant for this reaction. The reactions with H are fast, proceeding at 17%–66% of the collisional rates. No ionic products were observed for any of the reactions studied. While associative detachment is exothermic for all three anions, other reactive detachment processes are also possible. These anions were found to be unreactive with H2.