Mechanism Of Electron Capture Research Articles

Gas Chromatographic Analysis of Toxic Edemagenic Inhalation Compounds

Abstract Different megabore column and packed column phases were evaluated for their suitability in the gas chromatographic analysis of three toxic polyhalogenated compounds (phosgene, TFD, and PFIB). Adsorbent type stationary phases provide better retention and separation for the volatile fluorocarbons than do polar and nonpolar liquid phases. The reactivity of phosgene precludes the use of many phases having hydroxy, amino, or cyano functional groups. Silica gel is still the column of choice for phosgene. The use of gas sampling bags and gas-tight syringes can provide reliable quantitation of these compounds in air samples. TFD and PFIB eexhibit different electron capture mechanisms and detector temperature dependency. The mechanisms are supported by the results of negative ion mass spectrometry.

Contributions of different mechanisms for electron capture at relattvistic impact energies

Electron capture by impact of bare projectiles on different targets at high relativistic collision energies is studied. Contributions to total cross sections, of experimental interest, given by various radiative and nonradiative intermediate mechanisms are analysed. The nonradiative reactions are represented by two center-distorted wave models.

Neutralization of fast protons after grazing scattering from AI(111)

Abstract We investigate the neutralization of fast protons (4 to 200 keV) after the interaction with a clean AI(111)-surface at grazing incidence (Φ < 1°). At projectile velocities of about 0.4 v 0 (v 0 = Bohr velocity) we observe almost total neutralization, while the neutral fraction decreases down to 2% at about 3 v 0. Model calculations in the framework of resonant electron transfer, which describe the charge exchange of alkali–ions at an aluminum surface fairly well, predict a much stronger decrease of neutralization with increasing projectile velocity than observed. We interpret this discrepancy by the presence of further electron capture mechanisms like Auger-neutralization, etc. The yield of negative ions is lower than 1% at all velocities and is satisfactorily reproduced by theory of resonant electron transfer.

Non-radioactive electron-capture detector for gas chromatography

This paper is an update on the progress made towards developing a practical electron-capture detector which does not require a radioactive source, can be operated in the pulsed mode, and can be used at temperatures up to 800 K. Data obtained using a prototype detector have been reported previously. In this paper results obtained with a “large-volume” but leak-free detector at elevated temperatures are reported, and preliminary data with a practical “small-volume” detector will be discussed. The temperature dependence suggests that the electron-capture mechanisms that have been demonstrated previously are also operative in the non-radioactive detector. The discharge has been examined spectroscopically. Finally, we present characteristic data for the detector under high-purity conditions. These data are similar to those obtained with a radioactive detector and serve as a “base case” for future development.

Pair production with electron capture in relativistic heavy-ion collisions

The creation of an e--e+ pair as an intermediate mechanism of electron capture in collisions between bare heavy ions at relativistic impact velocities is analysed. A distorted-wave model is developed to study the process. A two-centre Sommerfeld-Maue spinor is introduced to represent the positron as moving in the simultaneous presence of the projectile and target nuclei. Single differential cross sections are calculated as a function of positron energy. Comparisons are given with results obtained by using other theoretical approximations.

The electron swarm method as a tool to investigate multi-body electron attachment processes

The electron swarm method has been used for the investigation of multi-body thermal electron attachment process. Ethylene, carbon dioxide and their mixtures were used as carrier gases. The rate constant for the reaction of thermal electrons with SF 6 has been measured and found to be (2.5±0.2) × 10 -7 cm 3·mol -1·s -1. The mechanism and kinetics of thermal electron capture by N 2O was investigated in the mixtures with C 2H 4 and CO 2. A mechanism involving neutral van der Waals molecules (N 2O·CO 2) has been proposed and the rate constants calculated to be 1.9 × 10 -10 cm 3·mol -1·s -1 for the formation of (N 2O·CO 2) and 1.8 × 10 -30 cm 6·mol -2·s -1 for the three-body reaction with CO 2 as a stabilizing agent.

Importance of kinetics and thermodynamics to the electron-capture detector

The kinetic model for the electron-capture detector (ECD) has been reviewed. Emphasis was placed on the agreement between thermodynamic and kinetic data obtained from the ECD and independent data obtained by other techniques. During the past five years, sufficient kinetic and thermodynamic data have been obtained to establish clearly the validity of the ECD model for non-dissociative electron capture and for exothermic dissociative electron attachment. In addition, new ECD data have been obtained for a kinetic mechanism of dissociative electron capture, which had been postulated but had not been demonstrated. This mechanism provides values for rate constants which have heretofore never been measured. All of the mechanisms have been illustrated by the use of Morse potential energy curves. A direct correspondence was shown to exist between the gas-phase mechanisms and mechanisms in solution observed with electrochemical techniques. As a result, fundamental kinetic and thermodynamic data can be obtained from the solution data. Correlations have been given which permit the calculation of electron affinities from half-wave reduction potentials.

Correlated double electron capture in slow, highly charged ion-atom collisions

Recent measurements [1,2] of autoionization electrons produced in slow, highly charged ion-atom collisions are reviewed. Mechanisms for double electron capture into equivalent and nonequivalent configurations are analyzed by comparing the probabilities for the creation of L-Auger electrons and L 1L 23 X Coster-Kronig electrons. It is shown that the production of the Coster-Kronig electrons is due to electron correlation effects whose analysis leads beyond the independent-particle model. The importance of correlation effects on different capture mechanisms is discussed.

Pressure dependence of impurity levels in semiconductors: The deep gold acceptor level and shallow donor and acceptor levels in silicon.

The effects of hydrostatic pressure on the properties of the deep gold (Au) acceptor level and on the binding energies of shallow donors and acceptors in silicon are presented and discussed. The pressure dependences of the Gibbs free energy, enthalpy, and entropy associated with electron emission from the Au acceptor were determined from measurements of the electron emission rate and electron-capture cross section (${\ensuremath{\sigma}}_{n}$) as functions of pressure and temperature. The results allow determination of the breathing-mode lattice relaxation accompanying electron emission from this center. The relaxation is found to be relatively large and inward (i.e., contraction). This appears to be the first quantitative determination of this relaxation for any electronic level in any semiconductor. Other highlights of the results on the Au acceptor are the findings that (i) the energy of this level is pinned to neither the conduction- nor valence-band edges, contrary to earlier belief and (ii) ${\ensuremath{\sigma}}_{n}$, which is known to be temperature independent, is also pressure independent. This latter result is discussed in terms of possible mechanisms for nonradiative electron capture. For the shallow donors and acceptors, the pressure derivatives of the binding energies are over an order of magnitude smaller than those of the energy gap and the Au acceptor, i.e., these levels remain essentially pinned to their corresponding band edges, as expected. These results can be understood in terms of effective-mass theory.

Importance of kinetics and thermodynamics to the electron-capture detector

The kinetic model for the electron-capture detector (ECD) has been reviewed. Emphasis was placed on the agreement between thermodynamic and kinetic data obtained from the ECD and independent data obtained by other techniques. During the past five years, sufficient kinetic and thermodynamic data have been obtained to establish clearly the validity of the ECD model for non-dissociative electron capture and for exothermic dissociative electron attachment. In addition, new ECD data have been obtained for a kinetic mechanism of dissociative electron capture, which had been postulated but had not been demonstrated. This mechanism provides values for rate constants which have heretofore never been measured. All of the mechanisms have been illustrated by the use of Morse potential energy curves. A direct correspondence was shown to exist between the gas-phase mechanisms and mechanisms in solution observed with electrochemical techniques. As a result, fundamental kinetic and thermodynamic data can be obtained from the solution data. Correlations have been given which permit the calculation of electron affinities from half-wave reduction potentials.

OD ESR studies on the interaction of electrons with polar additions in liquid saturated hydrocarbons

The method of optically detected ESR has been employed to investigate the excess electron capture by clusters of polar additions, such as water and alcohols. The concentration and temperature dependences of the signal intensity and linewidth of OD ESR for solvated electrons, and also their variations due to deuteration, have made it possible to suggest a mechanism of electron capture by clusters. Experimental ESR and ESE data have been compared.

Electron capture in Ar++H

Electron capture in ${\mathrm{Ar}}^{+}$${(\mathrm{}}^{2}$P)${+\mathrm{H}}_{2}$(X ${\mathrm{}}^{1}$${\mathrm{\ensuremath{\Sigma}}}_{\mathrm{g}}$) collisions in the keV energy regime has been studied theoretically. The molecular-orbital expansion method was used within a semiclassical formalism and an electron translation factor correction was incorporated to the first order in the magnitude of the relative velocity V. The molecular wave function and eigenenergy were obtained using the diatoms-in-molecules (DIM) method. We have examined the effect of the orientation of the target ${\mathrm{H}}_{2}$ molecule on the electron-capture mechanism within the sudden adiabatic approximation. Since \ensuremath{\pi} symmetry arising from the p orbital of the ${\mathrm{Ar}}^{+}$ ion is involved in this system, a strong influence on the probability of the molecular orientation was found in all energies studied. As the collision energy increases, the \ensuremath{\Pi}-symmetry state in the initial channel becomes more important through the rotational coupling to the electron-capture mechanism, while at lower energies the \ensuremath{\Sigma}-symmetry state in the initial channel is the dominant source for the electron capture through strong radial coupling. Agreement of the present theory with measurements is good, but marked disagreement is seen with the atomic-orbital calculation.

Molecular-state treatment of excitation and charge-transfer processes in H++He

The molecular-state expansion method within the impact-parameter formalism is applied to the processes ${\mathrm{H}}^{+}$+He(1${s}^{2}$) \ensuremath{\rightarrow}H(nl)+${\mathrm{He}}^{+}$(1s) and ${\mathrm{H}}^{+}$+He(1${s}^{2}$) \ensuremath{\rightarrow}${\mathrm{H}}^{+}$+He(1s,2l). Electron translation factors are incorporated into the scattering wave function, so that the cross sections obtained are free from the origin dependency. It is shown that stepwise flux promotion is the primary mechanism for excitation and electron capture into excited states at lower energies, and hence it is necessary to include all these channels in the close-coupling method to achieve reliable results.

Determination of elemental iodine by gas chromatography with electron capture detection

A gas chromatography/electron capture detector (GC/ECD) technique has been developed to determine elemental iodine in toluene and cyclohexane solvents. The retention index based on the alkyl iodide and n-paraffin series was determined. Sufficient resolution was obtained to resolve I/sub 2/ from alkyl iodides. A detection limit of 39 ng of I/sub 2/ was obtained. A dissociative electron capture mechanism was proposed for the ECD response to I/sub 2/. Radiotracer studies established the I/sub 2/ was transmitted through the column without conversion to an organic iodide. The utility of the developed technique was demonstrated on a AgI in NH/sub 4/OH mass spectrometry standard solution. An accuracy of 23% and a precision of 12% were demonstrated. 6 references, 8 figures, 2 tables.

Use of electron-capture data at short pulse intervals for study of electron-capture mechanisms

Electron-capture data obtained at short pulse intervals (50–100 μsec) cn be used to determine electron-capture mechanisms. The response function has been derived and it differs considerably from that at steady-state conditions. The electron-capture doefficient can be defined from the response function and it is directly proportional to the pulse frequency. The derived response function is in agreement with the experimental concentration, temperature, and pulse interval dependence.The response is independent of pulse width providing short pulse widths (0.5–1.0 μsec) are used at intervals larger than 50 μsec. The electron-capture coefficient at short pulse intervals is lower than at long pulse intervals where steady-state conditions prevail. However, this is partially compensated by a greater standing current at short pulse intervals.

A Localized Defect in InP with Strong Temperature Dependence of Capture Cross-Section

The properties of the localized deep-level MOE2 in InP have been investigated. The electron capture cross-section has a strong temperature dependence in the temperature range from 222 K to 276 K. A thermal depth of Et=0.15 eV and an optical depth of Eopt=0.48 eV have been obtained for MOE2 by normal and optical deep-level transient spectroscopy (DLTS). These results indicate that a Stokes shift, which is characteristic of strong electron-phonon coupling, occurs at the MOE2 level. The experimental results on the temperature-dependent capture cross-section can be explained fairly well by the recently-formulated multiphonon emission electron capture mechanism.

Constant current linearization for determination of electron capture mechanisms

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTConstant current linearization for determination of electron capture mechanismsAlbert. Zlatkis, C. K. Lee, W. E. Wentworth, and E. C. M. ChenCite this: Anal. Chem. 1983, 55, 9, 1596–1599Publication Date (Print):August 1, 1983Publication History Published online1 May 2002Published inissue 1 August 1983https://doi.org/10.1021/ac00260a034RIGHTS & PERMISSIONSArticle Views77Altmetric-Citations25LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (473 KB) Get e-Alerts Get e-Alerts

Exact second Born electron capture forp+He

Formulation and exact numerical calculation of differential and total $1s\ensuremath{-}1s$ electron-capture cross sections with the use of the second Born approximation with the free-wave Green's function are presented. At energies above 15 MeV there appears in the differential cross section a peak characteristic of a second Born or two-step process. For total cross sections, our calculations show that below 7 MeV the second-order cross section is larger than the first-order cross section, indicating a breakdown of second-order Born approximation with the free-wave Green's function. Results using the peaking approximation of Drisko converge to our exact second Born results only at energies well above 30 MeV. According to our exact second-Born calculations, observation of the angular distribution above 15 MeV should reveal structure related to at least one two-step mechanism for electron capture.

Effect on high-energy radiation on the pentacyanonitrosylferrate(II) ion in various glasses

A range of aqueous and non-aqueous glasses containing the pentacyanonitrosylferrate(II) ion (i.e. nitroprusside ion) have been exposed to 60Co γ-rays at 77 K. Electron addition is an efficient process, and gives rise to two major species detected by ESR spectroscopy. One involves electron addition at the NO ligand (species II) and the other involves addition to iron to give a d 7 complex (species I). On annealing these species remain without change until near the glass softening points, when species II is converted irreversibly into I. For strongly aqueous systems this thermal change only occurs on melting. The mechanism of electron capture and the structures of species I and II are discussed.

Inner-shell alignment of atoms in ion-atom collisions. II. Electron capture

For pt.I see ibid., vol.13, p.1601 (1980). The alignment of ions with an inner-shell vacancy resulting from electron capture in ion-atom collisions is treated theoretically. The general expressions for the alignment are obtained in the Oppenheimer-Brinkman-Kramers and Born approximations. Simple analytical formulae for the alignment are derived within the framework of the hydrogenic model. The dependence of the degree of alignment on the incident particle velocity and the ratio of charges of the colliding particles is analysed. The alignment due to electron capture is shown to differ essentially from the alignment due to direct Coulomb ionisation. The sensitivity of the degree of alignment to the form of captured-electron wavefunctions and to the type of perturbing interaction is investigated. The experimental data on the angular distribution of Auger electrons in the ionisation of the 2p3/2subshell of Mg by protons and He+ ions are reanalysed taking into account the electron capture mechanism.