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  • 1
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    The spectroscopic foundation of radiative forcing of climate by carbon dioxide (2016)
    Wiley
    Details
    Publication Date: 2016-04-23
    Description: The radiative forcing (RF) of carbon dioxide (CO 2 ) is the leading contribution to climate change from anthropogenic activities. Calculating CO 2 RF requires detailed knowledge of spectral line parameters for thousands of infrared absorption lines. A reliable spectroscopic characterization of CO 2 forcing is critical to scientific and policy assessments of present climate and climate change. Our results show that CO 2 RF in a variety of atmospheres is remarkably insensitive to known uncertainties in the three main CO 2 spectroscopic parameters: the line shapes, line strengths, and half widths. We specifically examine uncertainty in RF due to line mixing as this process is critical in determining line shapes in the far wings of CO 2 absorption lines. RF computed with a Voigt lineshape is also examined. Overall, the spectroscopic uncertainty in present-day CO 2 RF is less than one percent, indicating a robust foundation in our understanding of how rising CO 2 warms the climate system.
    Print ISSN: 0094-8276
    Electronic ISSN: 1944-8007
    Topics: Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 2
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    Abscisic Acid Induces Formation of Floating Leaves in the Heterophyllous Aquatic Angiosperm Potamogeton nodosus (1978)
    American Association for the Advancement of Science (AAAS)
    Details
    Publication Date: 1978-09-22
    Description: Potamogeton nodosus tubers produce floating-type instead of submersed-type leaves when exposed to 10(-5) molar synthetic abscisic acid. Abscisic acid-induced leaves have stomata on upper leaf surfaces and higher width/length ratios than controls. These effects are wholly or partially overcome by simultaneous exposure to abscisic acid combined with gibberellic acid, kinetin, or benzyladenine.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Anderson, L W -- New York, N.Y. -- Science. 1978 Sep 22;201(4361):1135-8.〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/17830317" target="_blank"〉PubMed〈/a〉
    Print ISSN: 0036-8075
    Electronic ISSN: 1095-9203
    Topics: Biology , Chemistry and Pharmacology , Computer Science , Medicine , Natural Sciences in General , Physics
    Published by American Association for the Advancement of Science (AAAS)
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  • 3
    Electronic Resource
    Electronic Resource
    Selenium in North American paper pulps (1974)
    s.l. : American Chemical Society
    Environmental science & technology 8 (1974), S. 462-464 
    Details
    ISSN: 1520-5851
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology , Energy, Environment Protection, Nuclear Power Engineering
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1021/es60090a014
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  • 4
    Electronic Resource
    Electronic Resource
    Measurement of C6H6 densities in a diamond deposition system (1999)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 110 (1999), S. 4647-4650 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We report the absolute column densities of gas phase C6H6 and upper limits on absolute C4H2 and C2H3 concentrations in a hot filament diamond chemical vapor deposition (CVD) reactor. The steady state density of C6H6 is monitored as a function of C2H2 and H2 input fractions. The C6H6 column density is a quadratic function of input C2H2 fraction at low C2H2 fractions. Above a critical C2H2 input fraction, the C6H6 column density becomes independent of C2H2 input fraction. The column density of gas phase C6H6 is relatively insensitive to the input H2 fraction. The weak relationship between C6H6 and H2 input fraction is in contradiction to the conclusion drawn from chemical kinetics modeling of diamond CVD that H2 strongly suppresses the formation of aromatic species under diamond CVD conditions. Moreover, comparison of C6H6 column densities with previously measured CH3 column densities under similar conditions indicate that a comparable fraction of gas phase carbon atoms in the steady state are incorporated in C6H6 as are incorporated in the growth species CH3. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.478347
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  • 5
    Electronic Resource
    Electronic Resource
    Effect of water vapor on a CH4-H2 discharge plasma (1989)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 55 (1989), S. 1385-1387 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The effects on a CH4 -H2 discharge plasma due to the addition of water vapor to the feed gas have been studied. Surprisingly it is found that the concentrations of most positive and negative hydrocarbon ions in the discharge are substantially increased. Possible mechanisms for the increase are presented.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.101602
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  • 6
    Electronic Resource
    Electronic Resource
    Atomic and radical densities in a hot filament diamond deposition system (1996)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 104 (1996), S. 9111-9119 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The gas phase densities of atomic carbon, atomic hydrogen, and methyl radicals are measured in a hot filament diamond deposition system by the use of absorption spectroscopy in the vacuum ultraviolet. The ratio of atomic to molecular hydrogen is also determined using the measured C and CH3 densities and the equilibrium constant for the hydrogen abstraction and recombination reactions that link the C and CH3 densities. The flux of C to the diamond surface is inadequate to explain the total growth rate, though C could have an important role in initiating growth. A model indicates that the hydrogen is dissociated at the filament and diffuses quickly throughout the rest of the system; gas phase reactions only have a small effect on the degree of dissociation. An increased input CH4 mole fraction results in lower hydrogen dissociation by poisoning the catalytic properties of the filament. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.471443
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  • 7
    Electronic Resource
    Electronic Resource
    Ultraviolet spectroscopy of gaseous species in a hot filament diamond deposition system when C2H2 and H2 are the input gases (1994)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 75 (1994), S. 3142-3150 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The methyl radical density, acetylene mole fraction, filament properties, and diamond growth rate and film quality are measured in a hot filament chemical vapor deposition system when C2H2 and H2 are used as the input gases. The methyl radical density and acetylene mole fraction depend greatly on the degree of filament surface poisoning. This poisoning prevents diamond growth due to a lack of hydrogen atoms and/or methyl radicals. Understanding the large influence of the filament surface catalytic characteristics is important for developing a gas phase model of this system. The results obtained with C2H2 and H2 as the input gases are compared to those obtained with CH4 and H2 as the input gases. Under conditions when the filament surface is not poisoned, the methyl radical concentrations are similar when either C2H2 and H2 are the input gases or when CH4 and H2 are the input gases.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.356169
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  • 8
    Electronic Resource
    Electronic Resource
    Apparatus for measuring electron-impact excitation cross sections using fast metastable atoms produced via charge exchange (1996)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 67 (1996), S. 2738-2751 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: An apparatus for measuring absolute cross sections due to electron-impact excitation out of the metastable levels of rare-gas atoms via the optical method is described with the focus specifically on excitation out of the 2 3S metastable helium level. The metastable helium target (He*) is prepared by charge exchange between 1.6 keV He+ ions and cesium vapor. An electron beam crosses the fast metastable beam target at a right angle and the fluorescence is collected at right angles to both beams. The charge transfer reaction produces He atoms mainly in the n=2 He levels. Because the target contains a negligible ground state He fraction, we can measure excitation cross sections from excitation threshold up to an arbitrarily high energy (keV regime) which represents a major improvement over previous metastable excitation cross sections measurements. The He* target density is extremely small (∼106 atoms/cm3) yielding minuscule signal rates. We describe steps taken to maximize the signal-to-noise ratio. We discuss the implications of using a fast beam target including both the finite flight time of the excited atoms across the light gathering region and the reduction of the cascade contributions to the apparent cross sections. A discussion of the identification and elimination of various systematic effects is also given. To measure absolute cross sections, we explicitly determine the spatial distributions of both the electron and metastable beams, as well as the spatially dependent response of the fluorescence gathering region. We determine the absolute flux of fast metastable atoms using a thermal detector calibrated with a He+ ion beam. As examples, we present absolute cross sections for excitation out of the 2 3S metastable level into the 3 3D and 4 3D levels. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1147102
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  • 9
    Electronic Resource
    Electronic Resource
    Gas temperature in a hot filament diamond chemical vapor deposition system (1996)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 67 (1996), S. 1546-1554 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: The gas temperature in a hot filament activated diamond chemical vapor deposition system is derived from the vacuum ultraviolet absorption spectrum of the H2 molecule. Curves of growth for the optically thick spectra are calculated using a Voigt line shape and published oscillator strengths in order to measure relative populations of H2 in various rotational and vibrational levels of the ground electronic state. The H2 vibrational levels are nearly in equilibrium. The gas temperature field is most strongly influenced by the substrate temperature. Heat conduction from the filament produces a large temperature gradient near the filament. Heat released or absorbed in gas phase hydrocarbon chemical reactions does not significantly affect the temperature field. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1146886
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  • 10
    Electronic Resource
    Electronic Resource
    Ultraviolet reflection–absorption spectroscopy of benzene on metal surfaces (2000)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 88 (2000), S. 4097-4101 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: This article reports on ultraviolet reflection–absorption spectroscopy of C6H6 molecules physisorbed on Ag, Cu, and Au surfaces. The electronic 1A1g→1B2u transition of C6H6 at wavelengths near 250 nm is observed. We model the system and obtain center frequencies, linewidths, and estimates of the oscillator strengths for the various vibronic absorptions. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1290711
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