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  • American Institute of Physics (AIP)  (3)
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  • 1
    Electronic Resource
    Electronic Resource
    Photofragmentation dynamics of formaldehyde: H2(v, J) distributions (1985)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 83 (1985), S. 4476-4487 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Coherent anti-Stokes Raman Scattering (CARS) is used to monitor the rovibrational population distribution of prompt H2 produced from H2CO+hν→H2+CO. Photolysis is performed on K=1 lines of the 2141 S1←S0 transition. Scanning CARS spectroscopy is employed, with suppression of the nonresonant background of the H2CO. The detection sensitivity is ∼1012 cm−3 per quantum state. Helium buffer is added to cool the product translation to near room temperature. States v=0–4, J=1–9 are detected. The vibrational distribution peaks at v=1. The rotational distributions in the vibrational states are somewhat Boltzmann with "temperatures'' ranging from 1700 to 2500 K for v=3–0. The total energy, 29 500 cm−1, is chosen near the threshold for dissociation. The internal energy of H2(v, J) sums with that found earlier for CO(v, J) and for translation to this total. An average impact parameter of 0.9 A(ring) with a spread of a few tenths A(ring) is found. H2 pushes away from a point about 0.3 A(ring) beyond the C nucleus of CO. The distributions are controlled by the dynamics of the fragments as they separate in the steep, repulsive exit valley of the potential energy surface; they are entirely different from the statistical distributions typical for bond fission without a barrier. Rotational relaxation of H2 in collisions with He occurs at 300 K with a rate constant of (9±3)×10−13 cm3 molecule−1 s−1 for J=3→J=1 and (2.6±1)×10−13 cm3 molecule−1 s−1 for J=5→J=3.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.449015
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  • 2
    Electronic Resource
    Electronic Resource
    Rovibrational molecular populations, atoms, and negative ions in H2 and D2 magnetic multicusp discharges (1985)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 82 (1985), S. 4943-4953 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Coherent anti-Stokes Raman scattering is applied to the study of rovibrational populations in magnetic multicusp H2 and D2 discharges. This subject is of interest to negative hydrogen ion formation by volume plasma processes. The populations of high-lying rotational states (J(approximately-greater-than)5) in the vibrational levels v=0, 1, and 2 are found to be significantly higher than expected from the Boltzmann law. In H2 the net populations of the first four vibrational levels follow approximately the Boltzmann law, with the vibrational temperature of 2390 K (in a 90 V-10 A discharge at 55 μbar). In similar discharge conditions, the population of the state v=3 in D2 is higher than expected from the Boltzmann law. In the presence of the discharge a deficiency in H2 and D2 molecule density was observed and was attributed to the possible presence of H and D atoms. This was verified by an independent measurement of the atomic fraction and temperature. The density of negative ions, measured by the photodetachment technique, is also reported.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.448668
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  • 3
    Electronic Resource
    Electronic Resource
    Real time diagnostics of detonation products from lead azide using coherent anti-Stokes Raman scattering (1991)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 59 (1991), S. 3516-3518 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We report on the first example that applies coherent anti-Stokes Raman scattering (CARS) to real time diagnostics of detonation products from a solid explosive. The supersonically expanding gaseous products, from the detonation of either lead azide pellets or powders, are studied, using broadband CARS. The density, and the rotational and vibrational temperatures of ground electronic state N2 molecules, N2(X), are monitored as a function of time at a fixed distance, 3.3 cm, from the azide surface. The rotational temperature is low, around 200–300 K, while the vibrational temperature is around 2000 K for delays of 8–12 μs, following the initiation of detonation. The density of N2(X), during this time interval, increases from ∼1×1017 to 1×1018 cm−3.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.105667
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