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  • 1
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 65 (1989), S. 1858-1865 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The drift velocity of electrons (w) in SiF4 and BF3 has been measured over the density-reduced electric field (E/N) range 0.5×10−17 V cm2 ≤E/N≤300×10−17 V cm2 using a pulsed Townsend experimental technique. The electron attachment (η/N) and ionization (α/N) coefficients have also been measured in SiF4 and BF3 over the E/N range 30×10−17 V cm2 ≤E/N≤300×10−17 V cm2 in the same experiment. The electron drift velocities in these two gases exhibit regions of negative differential conductivity (NDC) similar to but smaller in magnitude than those in CH4 and CF4 . The effective ionization coefficient (α¯/N) has been obtained from the η/N and α/N measurements in both gases, from which the high-voltage limiting electric field strengths (E/N)lim have been found to be 123×10−17 V cm2 for BF3 and 121×10−17 V cm2 for SiF4. The significance of these results in modeling gas discharges for a number of technological applications is indicated.
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  • 2
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 63 (1988), S. 52-59 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: In general, the electron attachment rate constant ka (〈ε〉, T), as a function of the mean electron energy 〈ε〉 and temperature T for electronegative gases which attach electrons nondissociative ily, decreases greatly with T from room temperature to T(approximately-less-than)600 K, while the ka (〈ε〉, T) of electronegative gases which attach electrons dissociatively increases with increasing T. Based on recent studies at our laboratory on ka (〈ε〉, T), we investigated the variation with T (∼295–575 K) of the uniform field breakdown strength, (E/N)lim, for three classes of electronegative gases: (a) gases such as c-C4F8 (and c-C4F6, 1−C3F6) which attach strongly low-energy ((approximately-less-than)1 eV) electrons nondissociatively and for which ka (〈ε〉, T) decreases precipitously with T above ambient: (b) gases such as C2F6 and CF3Cl which attach electrons exclusively dissociatively and whose ka (〈ε〉, T) increases with T; and (c) gases such as C3F8 and n-C4F10 which attach electrons both nondissociatively and dissociatively over a common low-energy range and whose ka (〈ε〉, T) first decreases and then increases with T above ambient. The (E/N)lim(T) has been found to decrease significantly with T for (a), to decrease slowly with T for (c), and to increase slightly with T for (b). These changes in (E/N)lim follow those in ka (〈ε〉, T). A similar behavior is expected for other electronegative gaseous dielectrics in the respective three groups.
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  • 3
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 60 (1986), S. 24-35 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: An improved pulsed Townsend technique for the measurement of electron transport parameters in gases is described. The accuracy and sensitivity of the technique have been investigated by performing, respectively, electron attachment coefficient measurements in pure O2 over a wide range of E/N at selected O2 pressures and by determining the electron attachment and ionization coefficients and electron drift velocity in CH4 over a wide E/N range. Good agreement has been obtained between the present and the previously published electron attachment coefficients in O2 and for the drift velocity measurements in CH4. The data on the electron attachment coefficient in CH4 (measured for the first time) showed that with the present improved pulsed Townsend method, electron attachment coefficients up to 10 times smaller than the ionization coefficients at a given E/N value can be accurately measured. Our measurements of the electron attachment and ionization coefficients in CH4 are in good agreement with a Boltzmann equation analysis of the electron gain and loss processes in CH4 using published electron scattering cross sections for this molecule.
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  • 4
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 58 (1985), S. 3001-3015 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Gas mixtures for possible use in diffuse discharge switching applications require both high dielectric strength and specific electron transport properties in the conducting and the opening stages of the operation of the switch. In the conducting stage, the electron drift velocity must be large, and the electron loss processes (e.g., due to electron attachment and recombination) must be low so as to maximize the current in the discharge while maintaining low-discharge impedance. In the opening stage, strong electron attachment along with high dielectric strength is required of the gas mixtures in order to extinguish the discharge as quickly as possible (and, thus, achieve a fast opening time) and to prevent arcing occurring between the switch electrodes due to the high voltages induced across the switch in the opening phase. Measurements of the electron drift velocity, attachment, ionization and transverse diffusion coefficients, and high-voltage dielectric strengths of several gas mixtures proposed as candidates for use in diffuse discharge switching applications have been made and are reported and discussed.
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  • 5
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 83 (1985), S. 641-654 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The attachment of low-energy (〈10 eV) electrons to the open-chain i-C4F10, i-C5F12, neo-C5F12, and to the cyclic c-C4F8 and c-C5F10 perfluoroalkanes has been studied using a time-of-flight mass spectrometer (TOFMS) and a high pressure electron swarm technique as well as the TOFMS results reported earlier on c-C4F8 and i-C4F10. Both long-lived parent anions (autodetachment lifetimes τa 〉10−6 s) and dissociative attachment fragment anions were observed for these molecules in the mass spectrometric study. The relative cross sections for negative ion formation and the τa of the long-lived parent anions were measured as a function of electron energy in the mass spectrometric study. The absolute total electron attachment rate constants as a function of the mean electron energy have been measured in the swarm study and used to calculate the total electron attachment cross sections as a function of electron energy. Both studies have shown a strong dependence of dissociative and nondissociative electron attachment processes on the structure of the molecules studied. For neo-C5F12, the predominant anion is the fragment C4F−9. In contrast, for i-C4F10, i-C5F12, c-C4F8, and c-C5F10, the parent anions are stronger than any of the fragment anions. Energetic considerations have been employed to identify fragmentation mechanisms of the negative ion states (NISs) leading to the formation of the observed fragment anions and to deduce some thermochemical data. The positions of the NISs, the observed differences in the cross sections for parent and fragment anion formation, and the types of the fragment anions formed for the various molecules are discussed.
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  • 6
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 86 (1987), S. 693-703 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Measurements are reported of the electron attachment (ηT/N) and ionization (αT/N) coefficients for the perfluoroalkanes n-CNF2N+2 (N=1 to 4) over the density-reduced electric field (E/N) range 5×10−17≤E/N≤400×10−17 V cm2 using pulsed Townsend (PT) experimental techniques. The present ηT/N measurements are the first to be obtained for pure C2F6, C3F8, and n-C4F10 at low E/N values. The ηT/N measurements in C3F8 and n-C4F10 are dependent on gas pressure over a wide E/N range in agreement with previous high pressure electron attachment rate constant ka measurements in these gases. The dissociative and nondissociative electron attachment processes for C3F8 and n-C4F10 have been quantified from the pressure dependence of the measured electron attachment coefficients ηT/N as a function of E/N. The thermal electron attachment rate constants (ka)th and the high voltage limiting electric field strengths (E/N)lim obtained from the present measurements are in good agreement with previous literature values.
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  • 7
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 83 (1985), S. 1434-1434 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The fragmentation of HF−2 into HF and F− is discussed. The electron impact formation of HF−2 from fluoroether CF2HOCF2H is further discussed and the electron affinity of HF2 is given. (AIP).
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  • 8
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 90 (1989), S. 4879-4891 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The electron attachment rate constants ka for SF6 have been measured in dilute mixtures of SF6 in high pressure (〉1 atm) N2, Ar, and Xe buffer gases at room temperature (T≈300 K) over a wide E/N range (electric field strength to gas number density ratio), corresponding to mean electron energies 〈ε〉 from near thermal electron energies (≈0.04 eV) to 〈ε〉≈4.3 eV. Particular attention has been paid to the effects of space charge distortion, molecular impurities, and changes in the electron energy distribution function on the measured electron attachment rate constant values at the lower E/N values in these mixtures. The present measured thermal electron attachment rate constants in SF6/N2 and SF6/Xe gas mixtures are in excellent agreement with recent accurate measurements of these parameters in several SF6/buffer gas mixtures. At higher 〈ε〉 values, the present SF6/N2 measurements are in fair agreement with previous measurements, while no previous measurements using Ar and Xe buffer gases have been published. These measurements have been used in numerical two term, spherical harmonic Boltzmann equation analyses of the electron motion in these gas mixtures to obtain the low energy (〈10 eV) nondissociative and dissociative electron attachment cross sections for SF6. The present derived electron attachment cross sections are compared with recently measured and derived nondissociative and dissociative electron attachment cross sections for SF6. The primary value of the present results is in the large and overlapping 〈ε〉 ranges of the present ka measurements for the three buffer gases compared with that for SF6/N2 gas mixtures alone, which in turn, makes these measurements ideal for testing cross-section sets in SF6 for use in many applied studies.
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  • 9
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 57 (1985), S. 4377-4385 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The relationship between the pressure-dependent electron attachment rate constants which have been observed in 1-C3F6 and in several perfluoroalkanes and the uniform field breakdown strengths (E/N)lim in these gases is discussed. Also discussed are the various types of synergistic behavior in (E/N)lim which have been observed in binary dielectric gas mixtures. For the latter, a new mechanism is outlined which explains the synergism observed in several gas mixtures where the (E/N)lim values of the mixtures are greater than those of the individual gas constituents, which we call positive synergism. Model calculations are presented which support this mechanism and can be used to explain the pressure-dependent synergistic effects which have been reported in 1-C3F6/SF6 and other gas mixtures. Experimentally observed ion–molecule reaction processes for several gases are discussed which support the proposed mechanism. Based on this mechanism, we outline several conditions which must be fulfilled in order to observe positive synergistic behavior in dielectric gas mixtures.
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  • 10
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 60 (1986), S. 4335-4337 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Negative ion formation in pure CF4 and CF4/N2 gas mixtures is shown to proceed exclusively by dissociative electron attachment mechanisms at electron energies 〉4 eV in a high-pressure electron swarm experiment. These results are in contrast to a recent swarm study where CF4 was reportedly shown to attach electrons by transient parent anion formation processes at low electron energies ε≈0.5 eV. Possible sources of errors in that study are discussed.
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