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  • Electronic Resource  (12)
  • 1990-1994  (12)
  • 1
    Electronic Resource
    Electronic Resource
    CO product distribution from metastable levels of HCO X˜ 2A' prepared by stimulated emission pumping (1993)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 98 (1993), S. 5095-5098 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Vibrational and rotational distributions have been measured for the CO produced following dissociation of HCO prepared in metastable ground-state levels by stimulated emission pumping. The metastable levels are characterized by high vibrational excitation in the HC–O stretching coordinate. The CO (v=2) rotational distribution following dumping of population on the QR0(5) transition to the (0, 7, 0) level is rotationally cold and its distribution is in very good agreement with the theoretical prediction by Dixon. The linewidths for stimulated emission pumping transitions to the (0, 7, 0) and (0, 8, 0) levels are 1.0 and 1.6 cm−1, respectively. Since it is possible to prepare a wide variety of metastable HCO levels whose wave functions sample different regions of the HCO potential energy surface, measurement of the dissociation dynamics of HCO so prepared should provide a detailed picture of the potential surface at energies from 0–10 000 cm−1 above the dissociation limit.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.464966
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  • 2
    Electronic Resource
    Electronic Resource
    Unimolecular dissociation of hydrogen peroxide from single rovibrational states near threshold (1991)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 94 (1991), S. 889-898 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Infrared-optical double resonance excitation of hydrogen peroxide using the ν3+ν5 and ν2 + ν5 combination bands as intermediate levels prepares reactant molecules in single rotational states near the OO dissociation threshold. The band origins of the ΔvOH = 4 vibrational overtone transitions originating from these combination bands provide information on the anharmonicities between the OH stretch and the OO stretch and OOH bend, respectively. At low resolution the vibrational overtone transitions are clearly parallel bands of a near prolate symmetric top and can be assigned to zeroth-order J and K quantum numbers. At 0.1 cm−1 resolution the individual features in the vibrational overtone spectra appear as clumps of sharp lines centered at the frequencies of the zeroth-order symmetric top transitions. The number of components within a clump appears to be less than the total number of available vibrational states. The narrowest feature observed has a linewidth of 0.12 cm−1 and sets a lower bound of ∼35 ps on the lifetime of the dissociating molecule. As J increases from 1 to 21, the clumps of lines coalesce into a smooth Lorentzian envelope. The overall clump width decreases with J, reaching an asymptotic value of 0.67 cm−1 at J(approximately-equal-to)17. A model incorporating a J dependent density of bath levels that couple to the zeroth-order bright state predicts the observed changes in the vibrational overtone transitions with J. The rotationally resolved vibrational overtone spectra provide information on the time scale for the conservation of K of the dissociating molecule.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.459979
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  • 3
    Electronic Resource
    Electronic Resource
    Broad vibrational overtone linewidths in the 7νOH band of rotationally selected NH2OH (1990)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 93 (1990), S. 9194-9196 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Infrared–optical double-resonance spectroscopy of the 7νOH vibrational overtone level of NH2OH reveals 14 cm−1 wide spectral features. The product state distribution of the OH fragment subsequent to overtone excitation indicates that the 7νOH level of NH2OH is ∼128 cm−1 above the N–O bond dissociation energy. Comparison to HOOH overtone spectra at a similar excess energy suggests that the broad NH2OH linewidths result from vibrational state mixing at the 7νOH level and not from inhomogeneous structure or lifetime broadening of the dissociating molecules. The observation of 14 cm−1 overtone linewidths for a molecule the size of NH2OH suggests that the broad vibrational overtone transition linewidths in larger polyatomics may contain a substantial homogeneous component.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.459210
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  • 4
    Electronic Resource
    Electronic Resource
    Product energy partitioning in the unimolecular decomposition of vibrationally and rotationally state-selected hydrogen peroxide (1992)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 96 (1992), S. 5129-5136 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Infrared-optical double resonance prepares HOOH molecules in single rotational levels of the 6νOH, 5νOH+νOOH, 5νOH+νOO, and 4νOH+νOH' vibrational states which range from 3 to 2287 cm−1 of excess energy above the unimolecular dissociation threshold. Laser-induced fluorescence probes the nascent OH rotational state distributions from the decomposition of rovibrationally selected reactants. The nascent rotational state distributions reveal that both OH spin–orbit states can be populated by the decomposition of a single molecule and hence that electronic angular momentum is not conserved throughout the dissociation process. The product state distributions from reactants excited to the 6νOH and 4νOH+νOH' vibrational levels are generally in good agreement with the predictions of phase-space theory provided electronic angular momentum is treated statistically. Reactants decomposing from single rotational states in the 5νOH+νOOH combination level (and to a lesser extent the 5νOH+νOO level) show product state distributions which are systematically colder than phase-space theory predictions. This observation indicates that energy redistribution in vibrationally excited HOOH is not complete on the time scale of unimolecular decomposition.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.462894
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  • 5
    Electronic Resource
    Electronic Resource
    Rotationally resolved vibrational overtone spectroscopy of hydrogen peroxide at chemically significant energies (1990)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 93 (1990), S. 8620-8633 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: An infrared–optical double resonance scheme simplifies the room temperature 6νOH vibrational overtone spectrum of hydrogen peroxide and prepares highly excited reactant molecules in single rotational states for unimolecular reaction studies. First, an optical parametric oscillator excites the OH asymmetric stretch (ν5) and selects a single or small subset of rotational states. A visible dye laser pulse then promotes molecules from vOH=1 to vOH=6 where they subsequently dissociate to produce two OH fragments. A third laser detects the dissociation products via laser induced fluorescence. The rotationally resolved vibrational overtone spectra of hydrogen peroxide generated by scanning the visible dye laser frequency are assignable to a parallel band of a near prolate symmetric top. Linewidths of the individual rovibrational features range from 1–3 cm−1 but show no systematic dependence upon the rotational quantum numbers and are attributed predominantly to anharmonic coupling of the zeroth-order bright state to dark background states. The assignability of the double-resonance vibrational overtone spectra to J and K quantum numbers implies that K is conserved for at least a time determined by the linewidth of a single zeroth-order rovibrational feature.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.459249
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  • 6
    Electronic Resource
    Electronic Resource
    Vibrational overtone spectroscopy of the 4νOH+νOH' combination level of HOOH via sequential local mode–local mode excitation (1992)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 96 (1992), S. 5659-5667 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Sequential pumping of the local OH stretch vibrations in hydrogen peroxide using infrared-optical double resonance permits spectroscopic access to the 4νOH+νOH' combination level. Analysis of the rotationally resolved vibrational overtone spectra generated by this technique determines approximate rotational constants for this level and a value of 17 051.8±3.4 cm−1 for the O–O bond dissociation energy. The linewidths of individual zeroth-order rotational transitions increase sharply with increasing K and change from smooth Lorentzian profiles to clumps of individual lines. The K dependence of the clump widths suggests that an a-axis Coriolis interaction is the primary coupling mechanism between the zeroth-order bright state and dark bath states. As a function of increasing J, each clump coalesces into a smooth Lorentzian profile. We interpret this J dependence in terms of a model that includes rotationally induced vibrational coupling among zeroth-order dark states.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.462665
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  • 7
    Electronic Resource
    Electronic Resource
    Variational estimates of chiral order parameter in 1+1 dimensional lattice QCD (1991)
    Springer
    The European physical journal 51 (1991), S. 423-427 
    Details
    ISSN: 1434-6052
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract We discuss analytically the vacuum structure and chiral-symmetry breaking in 1+1 dimensional lattice QCD with naive and Wilson fermions, using a unitary transformation and the variational method developed recently. As an example, the chiral order parameter is evaluated systematically for any coupling constant and fermion mass by including the multilink-terms in the transformation. The expected scaling behavior is observed. Our results are consistent with the continuum predictions.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01548566
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  • 8
    Electronic Resource
    Electronic Resource
    CO-laser photoacoustic detection of phosgene (COCl2) (1991)
    Springer
    International journal of infrared and millimeter waves 12 (1991), S. 141-147 
    Details
    ISSN: 1572-9559
    Keywords: CO laser ; COCl2 ; Photoacoustic spectroscopy
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Detection of COCl2, a highly toxic gas in chemical industry, using laser photoacoustic spectroscopy is presented. The spectrophone system used has a broad band LN2 cooled CW CO laser as a source of radiation, which operates from 4.8–8.4 um in the mid-infrared. Using an extracavity open longitudinal resonant cell, absorption signals to about 30 CO laser lines in the 5.45 um region could be observed. detection sensitivity has been estimated to be ppb order.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01009888
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  • 9
    Electronic Resource
    Electronic Resource
    Crack growth on elastic-plastic bimaterial interfaces (1992)
    Springer
    International journal of fracture 57 (1992), S. 365-379 
    Details
    ISSN: 1573-2673
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract Finite element calculation based on finite strain theory is carried out to simulate the crack growth on bimaterial interfaces under the assumption of small scale yielding and plane strain condition. The modified Gurson's constitutive equation and the element vanish technique introduced by Tvergaard et al. are used to model the final formation of an open crack. The crack growths in homogeneous material and in bimaterials are compared. It is found from the calculation that the critical macroscopic fracture toughness for crack growth J IC is much lower in bimaterials than in homogeneous material. For bimaterial cases, the J IC of a crack between two elastic-plastic materials which have identical elastic properties with different yield strength is lower than that of a crack between an elastic-plastic material and a rigid substrate. It seems that the difference in yield strength between the dissimilar materials has more significant influence on the void nucleation and crack growth than the difference in hardening exponent.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00013059
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  • 10
    Electronic Resource
    Electronic Resource
    66. Messung des Wärmeübergangskoeffizienten und des axialen Dispersionskoeffizienten in Wärmeaustauschern mit Hilfe einer Temperaturschwingungsmethode (1993)
    Weinheim : Wiley-Blackwell
    Chemie Ingenieur Technik - CIT 65 (1993), S. 1090-1091 
    Details
    ISSN: 0009-286X
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/cite.330650968
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