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  • 1
    Electronic Resource
    Electronic Resource
    Electron degradation and yields of initial products. VIII. Subexcitation electrons in H2 and D2 gases (1991)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 94 (1991), S. 8244-8251 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The moderation of subexcitation electrons in H2 and D2 is investigated by using the Spencer–Fano (SF) equation and the continuous-slowing-down approximation (CSDA). Cross-section data are adopted from the compilation by Buckman and Phelps [J. Chem. Phys. 82, 5001 (1985)]. Throughout, we focus on isotope effects, i.e., differences between H2 and D2, and consider electrons at energies appreciably higher than thermal energy. In summary, because vibrational and rotational excitation channels have lower thresholds in D2, subexcitation-electron behavior in D2 at energies below 0.6 eV shows different characteristics from that in H2. The moderation rate in H2 is larger than that in D2 by a factor of about 1.7. This difference is close to but not exactly the factor of 2 expected from an elementary estimate.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.460108
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  • 2
    Electronic Resource
    Electronic Resource
    Electron degradation and yields of initial products. III. Dissociative attachment in carbon dioxide (1988)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 89 (1988), S. 6220-6225 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We demonstrate the importance of subexcitation electrons in CO2 (with energies below 6 eV) by studying the yield of negative-ion formation in the dissociative attachment process e−+CO2→CO+O−. We evaluate the electron degradation spectrum and the time dependence of the degradation process within the continuous-slowing-down approximation. Slowing down by vibrational and other excitation collisions and the O− production are competing processes. This explains why the O− yield is larger for subexcitation electrons with energies above 3.8 eV, which avoid the large energy loss by electronic excitation and can still pass through the resonance at about 4 eV. The attachment at 8 eV with a much larger resonance-like cross section contributes only about 30% to the total O− yield in the degradation process.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.455728
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  • 3
    Electronic Resource
    Electronic Resource
    Electron degradation and yields on initial products. II. Subexcitation electrons in molecular nitrogen (1988)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 89 (1988), S. 7229-7237 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Subexcitation electrons lose their kinetic energy through vibrational excitation, rotational excitation, and elastic collisions in molecular gases. Initial yields of vibrationally and rotationally excited states of nitrogen molecules are calculated by using the Spencer–Fano equation (SFE) and its simplification, the continuous-slowing-down approximation (CSDA), both in time-independent and time-dependent representations. One focus of the present study is a close comparison of the CSDA with the rigorous treatment of the SFE in the subexcitation domain. The present result reveals for the first time distinct energy regions in which either vibrational excitation or rotational excitation dominates. This recognition explains the different time dependence of the yields of vibrational and rotational excitation.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.455302
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  • 4
    Electronic Resource
    Electronic Resource
    Analytic representation of secondary-electron spectra (1987)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 87 (1987), S. 6967-6972 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The secondary-electron spectrum, or the energy distribution of the ejected electrons resulting from charged-particle impact, is a crucial input to the microscopic modeling of radiation actions. The present article shows a general method for systematizing a bulk of data on the secondary-electron spectrum into a small number of indices. Our method is based on firm theoretical grounds, i.e., on thorough examination of the mathematical physics that governs the secondary-electron spectrum. We present several examples of the analysis of recent experimental data for proton impact.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.453392
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  • 5
    Electronic Resource
    Electronic Resource
    Theory of initial yields of ions generated by electrons in binary mixtures. II (1987)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 86 (1987), S. 3870-3875 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Eggarter [J. Chem. Phys. 84, 6123 (1986)] showed a method of calculation of the yield of ionization in a mixture by electrons, and carried out a numerical solution for the Ar–H2 mixture. At sufficiently high electron energies, the yields NAr and NH2 of each component species closely follow the relation NAr/NH2 =K⋅CAr/CH2, where CAr and CH2 represent the concentration fractions, and K is a constant. We now present a theoretical interpretation of that relation, and show the microscopic meaning of the constant K; it is the ratio of the ionization cross sections of the two component species, evaluated for an electron of a certain kinetic energy, which is much greater than the ionization threshold energy. The interpretation rests on the fact that the Spencer–Fano electron degradation spectrum depends on electron energy only mildly and smoothly except near the initial source energy and near the first ionization threshold energy. The same relation should hold approximately for any combination of ordinary molecules, although for the Ar–H2 case the relation is obeyed especially close. We also discuss the connection of our treatment with earlier treatments based on certain assumptions about the radiation-energy partition among the mixture components.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.451947
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  • 6
    Electronic Resource
    Electronic Resource
    Electron degradation and yields of initial products. IV. Subexcitation electrons in molecular oxygen (1989)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 90 (1989), S. 3081-3086 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Electron slowing-down processes in molecular oxygen gas in the subexcitation domain (below the ionization threshold) are studied by using the Spencer–Fano (SF) equation and its simplification, the continuous-slowing-down approximation (CSDA), both in time-dependent and time-independent representations. Compared to the previously studied cases of N2 and CO2, O2 has the special features in its inelastic cross sections of (i) strong delta-function-like peaks in the vibrational excitation cross section below 1.3 eV and (ii) very low energy thresholds of electronic excitation channels. These features provide a stringent test for the CSDA. Indeed, our results clearly show for the first time that the CSDA fails even qualitatively to reproduce the electron degradation spectrum given by the exact SF method over the whole energy regime studied.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.456652
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  • 7
    Electronic Resource
    Electronic Resource
    Electron degradation and yields of initial products. I. Excited species generated by electrons in binary mixtures (1987)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 87 (1987), S. 3875-3879 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Initial yields of excited species resulting from electron degradation in Ar+H2 mixtures have been calculated using the Fowler equation. Following up the previous study of yields of ions by Eggarter [J. Chem. Physl 84, 6123 (1986)] and by Inokuti and Eggarter [J. Chem. Phys. 86, 3870 (1987)], the present work treats initial yields of excited species over the entire range of the composition of Ar+H2 mixtures. The variation of the yield with the composition depends on the kind of excited species. The most noteworthy of the results obtained concerns the Ar metastable-state yield, which shows peculiar behavior when a small amount of H2 is introduced in the media.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.452942
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  • 8
    Electronic Resource
    Electronic Resource
    Analytic representation of the dipole oscillator-strength distribution. II. The normalization factor for electron continuum states in atomic fields (1985)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 82 (1985), S. 4415-4425 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We address ourselves to the question what analytic formula is the most suitable for fitting the dipole oscillator-strength distribution df/dε over a wide range of the kinetic energy ε of an electron ejected from an atom or molecule. A suitable expression will enable one to interpolate or extrapolate data reliably and to use them readily in applications such as the modeling studies in radiation physics. It is useful to distinguish two factors that together constitute df/dε. The first factor is defined in terms of the dipole matrix element with respect to a final-state eigenfunction whose amplitude near the origin is independent of ε. As we showed earlier, this factor is analytic at all finite ε except at a singularity at ε=−I, where I is the ionization threshold energy. The other factor arises from the energy-scale normalization of the final-state eigenfunction, and is the object of the present discussion from several angles. First, we present a survey of numerical data for the s,p, and d states with 0≤ε≤5 a.u. for all atoms with Z≤38, evaluated within the Hartree–Slater potential model. Next, we discuss analytic properties of the normalization factor, which include its relation to the phase shift, and its behavior near a resonance. We also elucidate the connection of the continuum normalization with the bound-state normalization. Finally, we illustrate the significance of our findings in the practical fitting of the df/dε data in the presence of a resonance, taking the valence-shell ionization of Ar as an example.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.448744
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  • 9
    Electronic Resource
    Electronic Resource
    Time-dependent and temperature-dependent aspects of electron distribution functions: H, Ar, and Cs atomic gases (1995)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 102 (1995), S. 6552-6558 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Time-dependent and temperature-dependent aspects of the thermalization of electrons in atomic gases are studied by using the Boltzmann equation. H, Ar, and Cs gases were chosen for the present study because of the characteristic and significantly different dependences of their momentum-transfer cross sections on electron energy; H has a smoothly varying cross section, Ar has a conspicuous Ramsauer–Townsend minimum, and Cs has a resonance-like peak. The effects of these cross section shapes on electron distribution functions and degradation spectra are examined. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.469369
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  • 10
    Electronic Resource
    Electronic Resource
    Absence of resonances in the elastic scattering of electrons in molecular solids (1986)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 85 (1986), S. 6239-6240 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We explain why experiments by Sanche and co-workers show no resonance effects in the elastic scattering of electrons by solid N2, while the same effects are conspicuous in inelastic channels. Briefly stated, our idea is that, once an electron is captured by a molecule in condensed matter, its charge induces an electric polarization of many neighboring molecules. The nuclear displacements arising from this polarization are unlikely to relax promptly upon electron autodetachment, thus dissipating part of the electron's initial energy. We point out some consequences of our interpretation in contexts of interest to radiation physics and chemistry.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.451496
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