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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
    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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  • 5
    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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  • 6
    Electronic Resource
    Electronic Resource
    Electron energy distribution functions and thermalization times in methane and in argon–methane mixtures: An effect of vibrational excitation processes (1995)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 103 (1995), S. 7104-7113 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Electron thermalization in methane and argon–methane mixtures is studied by using the Boltzmann equation. The presence of low-lying vibrational excited states in methane significantly changes electron energy distribution functions and relaxation times. We found that (i) the mean electron energy just below the first vibrational excited state is reached faster by 1000 times when the vibrational states are taken into account, and (ii) electron energy distribution functions have distinct peaks at energy intervals equal to the vibrational threshold energies. Both these effects are due to large vibrational stopping cross section. The thermalization time in mixtures of argon–methane (without vibrational states) smoothly changes as the mixture composition varies, and no significant difference in the electron energy distribution function is observed. When the vibrational excited states are taken into account, thermalization is almost completely defined by CH4, even at very low fractional concentrations of CH4. The sensitivity of the electron energy distribution functions on the momentum transfer cross sections used in calculation on the thermalization is discussed. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.470339
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  • 7
    Electronic Resource
    Electronic Resource
    Scattering angle dependence of electron impact excitation: Intensity variation within a vibrational progression (1995)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 102 (1995), S. 1561-1568 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Intensity distributions of electronic transitions in O2 and CO within a vibrational progression resulting from electron impact excitation are studied theoretically and experimentally. The multireference single- and double-excitation configuration interaction (MRD-CI) method is used to elucidate details of selected electronic transitions. In particular, the adiabatic MRD-CI approach can account for the variation of the Franck–Condon envelope with scattering angle that has been reported for the B 1Σ+←X 1Σ+ transition in CO and also was recently observed in the B' 3Σ−u←X 3Σ−g transition of O2. This behavior contrasts with the relative stability of the intensity distribution observed within the CO A 1Π←X 1Σ+ vibrational progression. In the former cases the excited state undergoes changes with internuclear separation because of the presence of an avoided crossing. Since a transition from the zeroth vibrational level in the ground electronic state to an individual vibrational level in the excited electronic state tends to select a particular internuclear distance (R centroid), each vibrational band may behave as a transition to a separate electronic level. This happens because the excited-state wave function undergoes a compositional change with internuclear separation between the adiabatic partners of the avoided crossing. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.468888
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  • 8
    Electronic Resource
    Electronic Resource
    Potential curves and nonadiabatic matrix elements for collisions involving fragments of the HeN+ molecular ion (1995)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 102 (1995), S. 7540-7548 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Ab initio multireference CI calculations have been carried out for the HeN+ molecular ion in order to describe collision processes between its constituent neutral and ionized atoms. The accuracy of these calculations is evaluated by means of a comparison of results obtained at large internuclear separations with the corresponding asymptotic energies deduced from atomic spectral data. Energy values are computed for the eleven lowest He++N and He+N+ atomic limits and average discrepancies relative to the experimental excitation energies up to 110 000 cm−1 are found to lie in the 1000–3000 cm−1 range, of which only 200 cm−1 appears to be the fault of the configuration interaction (CI) technique itself, with the main portion of the error stemming from the choice of atomic orbital (AO) basis instead. The HeN+ X 3Σ− ground state is calculated to have a De value of only 1414 cm−1, but the excited 2 3Π state has a much larger value of 22 133 cm−1 by virtue of an avoided crossing with the lower state of this symmetry. The corresponding radial nonadiabatic coupling is responsible for a large cross section for an excitation process between the N+(3Pg)+He and N+(3Du)+He channels which indirectly provides an efficient electron-capture mechanism leading to the N(4Su)+He+ exit channel. Additional nonadiabatic matrix elements for rotational and spin–orbit coupling have also been obtained and analyzed, as well as transition moments between the various HeN+ molecular states calculated. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.469085
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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
    Electron thermalization in rare gases and their mixtures (1996)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 104 (1996), S. 8973-8988 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The time evolution and temperature dependence of electron energy distribution functions (EDFs) are studied in pure rare gases (He, Ne, Ar, Kr, Xe) as well as in their mixtures by using solutions of the Boltzmann equation. A clear difference between the gases having the Ramsauer–Townsend (RT) minimum in the momentum-transfer cross section, (RT gases: Ar, Kr, and Xe), and those without the RT minimum (non-RT gases: He and Ne) is pointed out. The influence of the position and the depth of the RT minimum on the EDF and time evolution is studied for three different initial electron energies. A formula proposed for describing thermalization time in a mixture is tested on (i) a non-RT–non-RT gas mixture, (ii) a RT–non-RT mixture and (iii) a RT–RT gas mixture. The linear combination of the reciprocal thermalization times in gas mixture with the component concentrations as weighting factors is found to be valid for gases with a similar energy dependence of the momentum-transfer cross section, σm, and also for all rare-gas binary mixtures if the initial electron energy is sufficiently below the RT minimum. Conspicuous deviations from the linear relationship are observed in mixtures of gases whose energy dependence of σm (or the stopping cross section) are different, and theoretical rationales for these findings are provided. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.471631
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