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  • Other Sources  (18)
  • 2005-2009  (1)
  • 1985-1989  (17)
  • 1
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    Electron impact excitation cross section studies of methane and acetylene (1987)
    In:  Other Sources
    Details
    Publication Date: 2011-08-19
    Description: The 40-200-nm emission features of electron-impact-excited CH4 and C2H2 are investigated experimentally using the crossed-beam apparatus and VUV calibration techniques described by Ajello et al. (1982 and 1985). The results are presented in extensive tables and graphs and characterized in detail. All of the features are attributed to the atomic dissociation fragments C I, C II, and H, and the long lifetimes and high kinetic energies of the excited H fragments are shown to truncate the H Lyman series near principal quantum number n = 10.
    Keywords: ATOMIC AND MOLECULAR PHYSICS
    Type: Journal of Chemical Physics (ISSN 0021-9606); 86; 2750-276
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  • 2
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    No cometesimals in the inner solar system (1988)
    In:  Other Sources
    Details
    Publication Date: 2011-08-19
    Description: Ultraviolet measurements made by Voyager 2, apparently showing a rapid decrease in hydrogen Lyman-alpha emission with distance from the sun, were taken by Donahue et al. (1987) as evidence for a source of atomic hydrogen in the very local interstellar medium (VLISM). The suggested source of the hydrogen is a class of small comets at solar distances of about 1 AU. This claim has been adduced as evidence for a theory that the earth is subject to a large influx of cometary material significantly affecting atmospheric evolution. The Voyager 2 data have been reanalyzed, and it is shown that no source of hydrogen in the VLISM is required other than the inflow of neutral atoms.
    Keywords: ASTROPHYSICS
    Type: Nature (ISSN 0028-0836); 335; 417-419
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  • 3
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    A reexamination of important N2 cross sections by electron impact with application to the dayglow - The Lyman-Birge-Hopfield band system and N I (1199.99 nm) (1985)
    In:  Other Sources
    Details
    Publication Date: 2011-08-19
    Description: The emission cross section (cascade plus direct excitation) and predissociation cross section for the Lyman-Birge-Hopfield band systems is experimentally measured. The results are compared to electron energy loss measurements of the direct excitation cross section. An analytic approximation to the measured cross section is obtained which demonstrates the extreme simplicity of the collision strengths at energies above the cross-section peak. Cross sections are also obtained for the FUV atomic nitrogen multiplets. Available cross sections for N I emission at 119.99 nm are discussed in detail.
    Keywords: GEOPHYSICS
    Type: Journal of Geophysical Research (ISSN 0148-0227); 90; 9845-986
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  • 4
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    Hydrogen emission from Jupiter: Hydrogen emission from sunlit atmosphere of Saturn (1987)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: Successful IUE observations of the equatorial sunlit atmosphere of Jupiter and Saturn have been obtained. Spectra containing atomic and molecular hydrogen and solar reflection continuum emissions have been analyzed, with the purpose of determining the long term temporal behavior of the electroglow process. Quantitative estimates have been established for the first time using a model analysis of the short wavelength region of the spectrum. Both systems show varying degrees of long term variability in hydrogen emission rate, but the time scale is too short to determine whether there is a dependence on solar cycle activity. As part of the emission modeling program, a preliminary point source spreading function for the IUE SWP instrument has been established, suggesting a wavelength dependence in spectral line width different from previous analyses. Further IUE observations are planned for both Jupiter and Saturn.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: NASA-CR-180245 , NAS 1.26:180245
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  • 5
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    The Saturn System as Observed by Cassini's Ultraviolet Imaging Spectrograph (2005)
    In:  CASI
    Details
    Publication Date: 2017-10-02
    Description: The Cassini Ultraviolet Imaging Spectrograph (UVIS) has major new findings in all aspects of Saturn science: Saturn, its rings, Titan and the icy satellites, and the Saturn magnetosphere. Dynamic interactions between neutrals, ions, rings, moons and meteoroids produce a highly structured and time variable Saturn system. Highlights and outstanding new results will be reported, focusing on Saturn s moons and their interaction with their environment. The UVIS is one of Cassini s suite of remote sensing instruments. The UVIS instrument includes channels for extreme UV (55 to 110 nm) and far UV (110 to 190 nm) spectroscopic imaging, high speed photometry of stellar occultations, solar EUV occultation, and a hydrogen/deuterium absorption cell. UVIS has detected products of water dissociation, neutral oxygen and OH, which dominate the Saturn inner magnetosphere, in contrast to Jupiter, and H fills the entire magnetosphere apparently extending through the magnetopause at far greater density than the ion population. The O and OH and a fraction of the H are probably the products of water physical chemistry, and derived ultimately from water ice. Observed fluctuations indicate close interactions with plasma sources. Sputtering from the satellites water ice surfaces is insufficient to supply the observed mass. Stochastic events in the E ring may be the ultimate source.
    Keywords: Lunar and Planetary Science and Exploration
    Type: Lunar and Planetary Science XXXVI, Part 5; LPI-Contrib-1234-Pt-5
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  • 6
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    Large time scale variation in hydrogen emission from Jupiter and Saturn (1988)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: The IUE and Voyager spacecraft observations of Jupiter and Saturn were combined to obtain a consistent measurement of temporal variation of the equatorial subsolar hydrogen emission. The outer planets appear to have rather independent behavior over time scales of the order of 10 yr, particularly in emission from the H Ly alpha line. The time interval from 1978 to the present shows variation of mean equatorial H Ly alpha brightness of 2 at Jupiter and 5 at Saturn. The relative magnitudes of the variations is sufficiently different to suggest that response to input from the Sun is at least nonlinear. The brightness of H2 band emission appears to be relatively more stable than H Ly alpha. There is evidence in IUE observations of a moderate increase in H2 band brightness with increasing time at Jupiter, in opposition to the variation in H Ly alpha.
    Keywords: ASTRONOMY
    Type: ESA, A Decade of UV Astronomy with the IUE Satellite, Volume 1; p 93-96
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  • 7
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    The Mercury atmosphere (1988)
    In:  Other Sources
    Details
    Publication Date: 2019-06-28
    Description: Data available on the composition of Mercury's atmosphere are reviewed, and the sources of these atmospheric components are considered. The known gaseous components in Mercury's atmosphere are H, He, O, Na, and K; among other gases likely to be present are H2 and H2O. Probable sources of these components are the solar wind for hydrogen and helium. The alkalis and water are considered to come from the evaporation of meteoroidal material, with a possible contribution to the former by sputtering and photosputtering.
    Keywords: LUNAR AND PLANETARY EXPLORATION
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  • 8
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    An explanation for the H Ly-alpha longitudinal asymmetry in the equatorial spectrum of Jupiter - An outcrop of paradoxical energy deposition in the exosphere (1985)
    In:  Other Sources
    Details
    Publication Date: 2019-06-28
    Description: An analysis of the Voyager EUV spectra of the Jupiter sunlit equatorial emissions shows no evidence for a substantial dependence of atomic hydrogen abundance on magnetic longitude, required by earlier theories of the H Ly-alpha longitudinal asymmetry. An explanation for the H Ly-alpha bulge phenomenon is advanced in this work that conforms to the observations and does not require a strong asymmetry in atomic hydrogen abundance. It is proposed that the H Ly-alpha bulge is caused by a combination of proton collisional transfer of H(2s) atoms in the H(2p) state, and production through recombination of H2(+) and H3(+), in an asymmetric ionosphere. According to the present model a large fraction of the observed H Ly-alpha emission from the equatorial region is electron excited, at least at times of solar maximum.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Journal of Geophysical Research (ISSN 0148-0227); 90; 2673-269
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  • 9
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    Electron impact excitation of H2 - Rydberg band systems and the benchmark dissociative cross section for H Lyman-alpha (1985)
    In:  Other Sources
    Details
    Publication Date: 2019-07-12
    Description: The cross sections sigma R 1 (2p) for excitation of H Ly-alpha emission produced by electron impact on H2 is reexamined. A more accurate estimate for sigma R 1 (2p) is obtained based on Born approximation estimates of the H2 Rydberg system cross sections using measured relative excitation functions. The obtained value is (8.18 + or -1.2) x 10 to the -18th sq cm at 100 eV, a factor of 0.69 below the value universally applied to cross section measurements over the past decade. Cross sections for the H2 Rydberg systems fixed in magnitude by the Born approximation have also been obtained using experimentally determined excitation functions. Accurate analytic expressions for these cross sections allow the direct calculation of rate coefficients.
    Keywords: ATOMIC AND MOLECULAR PHYSICS
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 296; 765-773
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  • 10
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    Vacuum ultraviolet studies of electron impact of helium Excitation of He n1P0 Rydberg series and ionization-excitation of He(+) nl Rydberg series (1985)
    In:  Other Sources
    Details
    Publication Date: 2019-07-12
    Description: The cross sections for the He I 1s2 1S-1snp 1P0 series have been measured using a relative flow method, with the absolute scale fixed by the H Ly-alpha dissociative excitation cross section standard. The results are compared with those obtained using a relative cross section data analysis by modified Born approximation, and good agreement is found. Cross sections for the ionization-excitation of the He II 121.51 nm and He II 164.04 nm transmissions have been measured, and the results strongly suggest that theoretical calculations of the reactions differ fundamentally from physical reality. The failure of the theory to describe experimental results stems from the neglect in the theory of electron correlation effects between the two orbital electrons.
    Keywords: ATOMIC AND MOLECULAR PHYSICS
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 296; 774-783
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