Electron-ion Recombination Coefficient Research Articles

Experimental determination of the electron-avalanche and the electron-ion recombination coefficient

The electron-ion recombination coefficient γ and the avalanche coefficient δ = ( α − a) · v d , where α and a are the ionizat ion and attachment coefficients respectively and v d the drift velocity of the electrons, have been experimentally determined in a self-sustained CO 2-laser system (1:1:3 mixture) as a function of the E/ N value. For low voltages we found the expected decrease of the recombination coefficient for increasing E/ N values. However, it appears that for larger voltage the recombination coefficient increases sharply for increasing E/ N values. The measurements of δ show a much smaller value than expected from theoretical calculations. This must be explained by a lower value of the electron-energy distribution function for higher energies, which may be consistent with our measured high recombination probability for electrons having high energy.

E-beam initiated discharges in high-pressure Hg vapors

Studies are reported of stable glow discharges in high-pressure Hg vapors (?2 amagats) produced by a 20-nsec ionizing electron beam pulse. The discharges were very stable and operated for 4–5 μsec after the e-beam initiating pulse at E/N values up to 8×10−17 V cm2 and discharge current densities of 4 A/cm2. Power loadings of 3–6 kW/cm3 were typically obtained. An electron recombination coefficient of 7.4×10−9 cm3 sec−1 was measured. Strong continuum radiation from both the visible (4900 Å) and UV (3350 Å) bands of molecular Hg were observed. Absorption measurements from 4000 to 6764 Å are presented. No gain in this spectral region was ever detected. A peak absorption cross section at 4800 Å was estimated to be 2×10−16 cm2. The implication of this absorption on other potential laser systems employing Hg as a buffer gas are discussed.

Relation of electric discharge parameters to short-pulse CO2laser efficiency

A study is reported of the choice of the discharge and gas mixture parameters of an electron-beamsustained nanosecond CO2 laser with the aim of achieving maximum efficiency. An analysis is made of the dependence of the efficiency of such a CO2 laser on the composition and pressure of the gas mixture, properties and parameters of the discharge, electron and ion recombination coefficients, energy transfer between CO2, N2, and He levels, etc.

Saturation of impurity photoconductivity in n-GaAs with intense YAG laser light

We report the observation of saturation of impurity photoconductivity in semiconducting n-GaAs illuminated by a Q-switched Nd:YAG laser with light intensity up to 3.5 MW/cm2. From the saturation of conductivity we determined the concentration of defects to be ≈1016 cm−3. These form the well-known 1.2-eV absorption band and are presumably Ga vacancies. The curve of photoconductivity versus light intensity can be fitted with a simple model, which yields the electron recombination coefficient. The relation of the absorption band to nonlinear optical studies in GaAs at 1.06 μ is reviewed.

Measurement of the ratio of electron mobility and recombination coefficients in an arbitrary gaseous mixture

Measurement of the ratio of electron mobility and recombination coefficients in an arbitrary gaseous mixture

Use of electron backscattering for smoothing the discharge in electron-beam-controlled lasers: Computations

The anode material in an electron-beam-controlled gas laser strongly influences the uniformity of the sustainer discharge, because the backscattering of the beam electrons from the anode is different for different atomic numbers. As a result of switching from aluminum to, for instance, uranium, there is a 60% increase in the ionization near the anode, according to Monte Carlo computations for a typical planar laser configuration. This effect can cause a 30–60% drop in the local electric field, depending upon the field dependence of the electron-ion recombination coefficient. As an example for studying this effect, we have considered a 150-keV beam passing through an 0.8-mil Ti window into a 26-cm-wide planar cavity containing a 3:2:1 mixture of He, CO2, and N2 at 1 atm and 293 K, with Eave=4.5 kV/cm. Window power loading, electron attenuation, electron energy distributions, and sustainer field distributions were calculated for the two different anode materials.

An electron attachment plasma instability

A new type of plasma instability is described in an electron-beam ionized discharge. This instability occurs in gas mixtures in which the dissociative attachment rate increases strongly with electric field. It has been observed experimentally in He:H2O 740:20 and in He:CO2 1:1 and 9:1 mixtures. The values of the ionization source function S and of the electric field E at which the wave instability occurs are predicted using a Fourier analysis of the linearized kinetic rate equations. This yields the condition for instability as S < (1/α)[Eδβ/δE) − β]2, where α is the electron-ion recombination coefficient and β is the electron neutral attachment rate.

Variations of theD-region aeronomical parameters under non-equilibrium conditions

In this paper an attempt is made to define the time variations of theD-region main aeronomical parameters under non-equilibrium conditions by using experimental data by the A3 method, phase-height method and satellite data for the short-wave X-radiation. The SID effect of day-time and time variations of 21 August 1969 electron concentrationN(t) and recombination coefficient α′(t) are investigated. It is shown that during SID effect α′(t) increases.

Studies of Light Emission in the Pulse Radiolysis of Gases: Electron-Ion Recombination in Nitrogen

An experimental method for studying ion recombination processes using pulse radiolysis is described. The electron-ion recombination coefficient in N2 (280–980 torr) has been determined to be 3± 0.6× 10−6cm3ion−1·sec−1 at 25°C by analysis of the light emitted by N2(C 3πu), which is produced in the neutralization reaction. This recombination coefficient obeys a T−1/2 dependence. The formation of O3 from an O2–SF6 system was used as a radiation dosimeter to obtain the concentration of ions produced by a pulse of 13 MeV electrons.

Theoretical Estimate of the Effective Recombination Coefficient in the D Region

In the presence of a large number of positive and negative ionic species, an analytical expression for the effective recombination coefficient of electrons in the D region is derived in the same from, a' = + lambda ( alpha /sub ion/), as is customarily used in the uppe r regions. Here, ( alpha /sub e/) is the electronic recombination coefficient averaged with weights proportional to the abundance of various kinds of positive ions, and ( alpha /sub ion/) is the weighted mean of the various ionic recombination coefficients according to the composition of positive and negative ions. The effective loss rate of electrons is given as (1 + lambda )a' in which the negative ion-electron ratio, lambda , changes in a wide range as a function of altitude. Under the assumption of a model atmosphere containing eight minor constituents, the density distributions of thirteen species of positive ions and seven species of negative ions as well as of electrons are calculated. Based on the result, the effective recombination coefficient is estimated to be 4.2 x 10/ sup -7/ cm/sup 3/ sec/sup -1/ a t the 80 km-level, 1.5 x 10/sup -6/ cm/sup 3/ sec/ sup -1/more » at 70 km, and 1 9 x 10/s up -5/ cma sec/sup -1/ at 60 km, while lambda increases rapidly with decreasing height, being about 5.3 x 10/sup -3/ at 80 km, 7.9 x 10/sup -1/ at 70 km, and 1.0 x 10/sup -1/ at 60 km in a daytime condition. The effective loss rate estimated is shown to be consistent with the results derived from observations of solar eclipse, SID, and PCA events. (auth)« less

He3+andHe4+in 300°K Helium Plasmas: Their Effect on Recombination Loss of Electrons

The work reported here establishes the existence of $\mathrm{He}_{3}^{}{}_{}{}^{+}$ and $\mathrm{He}_{4}^{}{}_{}{}^{+}$ at room temperature (300\ifmmode^\circ\else\textdegree\fi{}K) in a helium afterglow. The data presented in this paper indicate that the often-measured electron-ion recombination coefficient in 300\ifmmode^\circ\else\textdegree\fi{}K helium afterglows is mainly attributable to electron recombination with $\mathrm{He}_{3}^{}{}_{}{}^{+}$ rather than, as is usually assumed, with the dominant ion $\mathrm{He}_{2}^{}{}_{}{}^{+}$.

Electron-ion recombination in seeded combustion products

The possibility of attaining a high non-equilibrium electrical conductivity in a high velocity flow of combustion products is of interest from the point of view of MHD power generation. Experimental evidence and theoretical predictions of the electron-ion recombination coefficient, which is of critical importance in this context, are discussed. An experiment is described, in which combustion products seeded with potassium were accelerated through a nozzle to a supersonic velocity. The electrical conductivity was measured and found to be a factor of six lower than that expected from the J. J. Thomson 3-body recombination theory.

Electron-temperature, density and gas-temperature measurements in an argon afterglow

Microwave and spectroscopic methods of monitoring the time-varying density and temperature of the electrons, as well as the temperature of the neutral background gas, have been applied to an argon afterglow. Electron-ion recombination coefficients were extracted from the decay rate over the electron-density range 1013–1011cm−3, concerning which little information had previously been reported.

Origin of water cluster ions in theDregion

Laboratory studies of the ions produced by the addition of water vapor into flowing streams of O2+ (or NO+) ions have led to a vapor phase reaction scheme starting with O2+ that seems likely to be responsible for the formation of the observed water cluster ions H3O+, H5O2+, H7O3+, etc. in the D region of the earth's ionosphere. Experimental difficulties have precluded quantitative rate constant measurements so far, and in addition the D-region water vapor concentration is uncertain so that only a qualitative scheme is possible at this time. The O2(¹Δg) photoionization source recently proposed by Hunten and McElroy is presumed to be the necessary precursor O2+ source. The reaction scheme involves O4+ and O2+·H2O as intermediate ions; these ions are possibly present in observable concentrations in the D region. Nitrous acid (HNO2) production is proposed to be an end result of successive hydrations of atmospheric NO+. The hydration of the atmospheric NO+ and O2+ ions and the formation of O4+ are expected to increase somewhat the effective electron recombination coefficient in the ionosphere.

Direct Electron–Hole Recombination in Anthracene

Temperature studies of the recombination coefficient of holes and electrons in anthracene have been made. There was no significant change in the recombination coefficient in the temperature range room temperature to 130°C other than that predicted by the Thomson or the Langevin theories of recombination. Kinetic analysis shows that the recombination center (thought to be the charge-transfer state) must have a binding energy E1 − ECT and a lifetime β−1 such that E1 − ECT > 0.033 eV ln(10RmNc / β), where Rm is the measured recombination coefficient and Nc is the density of states in the lower conduction band.

Recombination, Attachment, and Ambipolar Diffusion of Electrons in Photo-Ionized NO Afterglows

Photo-ionized plasma afterglows of NO have been studied by combined microwave and mass-spectrometric techniques. Nitric-oxide-neon mixtures (5-65 mTorr NO, 2-7 Torr Ne) are contained in a 10-cm resonant cavity where they are ionized by a "single pulse" of Lyman-$\ensuremath{\alpha}$ radiation. A temporal spectrum of ions diffusing to the wall is obtained by a differentially pumped mass spectrometer and multichannel analyzer. Analysis of the electron-density decay curves obtained by microwave techniques to obtain an electron-ion recombination coefficient for N${\mathrm{O}}^{+}$ is complicated by the conversion of N${\mathrm{O}}^{+}$ to the dimer ion, ${(\mathrm{NO})}_{2}^{+}$. At sufficiently low densities of nitric oxide the ${(\mathrm{NO})}_{2}^{+}$ concentration becomes negligible, and the N${\mathrm{O}}^{+}$ wall current tracks the electron-density decay. From comparisons of experimental electron-density decay curves obtained under recombination-controlled conditions, with computer solutions of the electron-continuity equation, the values $\ensuremath{\alpha}(\mathrm{N}{\mathrm{O}}^{+})=(7.4\ifmmode\pm\else\textpm\fi{}0.7), (4.1\ifmmode\pm\else\textpm\fi{}{0.3}{0.2}), \mathrm{and} (3.1\ifmmode\pm\else\textpm\fi{}0.2)\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}7}$ ${\mathrm{cm}}^{3}$/sec, at $T=200, 300, \mathrm{and} 450\ifmmode^\circ\else\textdegree\fi{}$K, respectively, are obtained. From analysis of electron-density decay curves at higher densities of NO, where ${(\mathrm{NO})}_{2}^{+}$ is the dominant ion, the value $\ensuremath{\alpha}{{(\mathrm{NO})}_{2}}^{+}=(1.7\ifmmode\pm\else\textpm\fi{}0.4)\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}6}$ ${\mathrm{cm}}^{3}$/sec at $T=300\ifmmode^\circ\else\textdegree\fi{}$K is obtained. The three-body electron-attachment and ambipolar diffusion coefficients have been measured in pure NO (0.1-5 Torr) and are found to be $K=(1.3\ifmmode\pm\else\textpm\fi{}0.1)\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}31}$ ${\mathrm{cm}}^{6}$/sec and ${D}_{a}p=80\ifmmode\pm\else\textpm\fi{}16$ ${\mathrm{cm}}^{2}$ Torr/sec, respectively, at $T=300\ifmmode^\circ\else\textdegree\fi{}$K.

Etude des effets ionosphériques de l'éclipse de soleil du 30 mai 1965 utilisant les observations faites par sondage zénithal classique, en Polynésie

Many valuable ionograms have been obtained from two vertical sounding stations located in the Society Islands: the first station at Tahiti (fraction of obscured Sun's disk at ground level: 89 100 ) and the second one at Maupelia (fraction of obscured Sun's disk at ground level 99 100 ). These ionograms (those of Tahiti-Taravao at least) permitted real height determination by Schmerling's method. Electron production rate, recombination and attachment coefficients are deduced from consideration of the curves showing electron density variation as a function of time. Blanketing of the ionizing sources during periods of zero sunspot activity is a well-known phenomen. This fact can be assumed to give results a peculiar value.

Analytical study of theD-region response to solar flares monitored by Ariel satellite (UK-1)

An analytical study of the D-region response to solar flare X rays is presented. A basic formalism is improvised and developed to determine the ionization and absorption characteristics of the D region. This formalism is subsequently utilized to study the effects of solar flare X-ray spectra monitored by Ariel satellite during April–May 1962. Calculated values of electron number density and excess absorption are compared with available experimental data. Only the buildup phase of the disturbance is studied since no information is available on the decay phase of X-ray flares. The decay phase is discussed hypothetically in a few cases. More recent data on solar flare X rays can be analyzed in an identical fashion. It is also shown that an electron-ion recombination coefficient of 1–3 × 10−7 (400/T)1/2 cm³ sec−1 results in realistic estimates of ionospheric effects.

Carrier Generation and Recombination in Anthracene

The hole—electron recombination coefficient, 2–3×10−6 cm3/sec, in anthracene has been determined directly by observing the decay of photogenerated carriers as a function of time. From considerations of the magnitude of the recombination, it is concluded that carrier generation can be observed only after excitation to an almost free electron band above the lowest narrow tight-binding band. The experimental data of Castro and Hornig, and Kearns, are analyzed in terms of band-to-band transitions to this upper band. From considerations of the wavelength dependence, autoionization of the Frenkel exciton levels at these energies is shown not to be important. Theoretical considerations predict a very small quantum yield for the band-to-band transition. A small cross section is consistent with experiment.

Electron-Ion Recombination in Nitric Oxide in the Temperature Range 196 to 358°K

The recombination of ${\mathrm{NO}}^{+}$ ions with electrons was studied in photoionized nitric-oxide-neon gas mixtures. A pulsed hydrogen lamp with a lithium fluoride window produced the ionizing ultraviolet radiation, which was incapable of exciting or ionizing Ne. Following an ionizing pulse, the decay of electron density was measured by a microwave-cavity reflection technique. Low NO pressures, 0.5 to 80 mTorr, were used to reduce negative-ion formation, and high Ne pressures, up to 132 Torr, were used to reduce ambipolar diffusion. Highly purified gases and ultrahigh-vacuum techniques were employed. Mass-spectrometer identification of the positive ion in NO-Ne mixtures indicated the presence of only ${\mathrm{NO}}^{+}$ ions. Negative ions, predominantly ${\mathrm{NO}}_{2}^{\ensuremath{-}}$, were observed to increase in number rapidly as NO pressure increased above 3 mTorr, and the uncorrected electron-recombination coefficient, computed from plots of reciprocal frequency shift versus time, increased as NO pressure increased, very likely owing to the influence of negative ions. Correction for negative-ion and diffusion effects was made by use of a computer-aided analysis. The ${\mathrm{NO}}^{+}$-electron recombination coefficient, measured at NO pressures of 0.5 and 1.0 mTorr under conditions of small negativeion influence and at a gas temperature of 298\ifmmode^\circ\else\textdegree\fi{}K, is ${4.6}_{\ensuremath{-}1.3}^{+0.5}$\ifmmode\times\else\texttimes\fi{}${10}^{\ensuremath{-}7}$ ${\mathrm{cm}}^{3}$ ${\mathrm{sec}}^{\ensuremath{-}1}$. Similar measurements made at temperatures of 196 and 358\ifmmode^\circ\else\textdegree\fi{}K yield the values ${10}_{\ensuremath{-}4}^{+2}$\ifmmode\times\else\texttimes\fi{}${10}^{\ensuremath{-}7}$ and ${3.5}_{\ensuremath{-}0.5}^{+0.2}$\ifmmode\times\else\texttimes\fi{}${10}^{\ensuremath{-}7}$ ${\mathrm{cm}}^{3}$ ${\mathrm{sec}}^{\ensuremath{-}1}$, respectively. The results of this study together with other laboratory measurements suggest an approximate ${T}^{\ensuremath{-}1.2}$ dependence of the recombination coefficient.