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  • 1995-1999  (4)
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Years
Year
  • 1
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 103 (1995), S. 4953-4966 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Recently, Kiefer et al. [J. H. Kiefer, S. S. Kumaran, and S. Sundaram, J. Chem. Phys. 99, 3531 (1993)] studied shock-heated norbornene (NB) in krypton bath gas using the laser-schlieren technique and observed vibrational relaxation, unimolecular dissociation (to 1,3-cyclopentadiene and ethylene), and dissociation incubation times. Other workers have obtained an extensive body of high-pressure limit unimolecular reaction rate data at lower temperatures using conventional static and flow reactors. In the present work, we have developed a vibrational energy transfer-unimolecular reaction model based on steady-state RRKM calculations and time-dependent master equation calculations to satisfactorily describe all of the NB data (incubation times, vibrational relaxation times, and unimolecular rate coefficients). The results cover the temperature range from ∼300 to 1500 K and the excitation energy range from ∼1 000 to 18 000 cm−1. Three different models (based on the exponential step-size distribution) for the average downward energy transferred per collision, 〈ΔE〉down were investigated. The experimental data are too limited to enable the identification of a preferred model and it was not possible to determine whether the average 〈ΔE〉down is temperature dependent. However, all three 〈ΔE〉down models depend linearly on vibrational energy and it is concluded that standard unimolecular reaction rate codes must be revised to include energy-dependent microcanonical energy transfer parameters. The choice of energy transfer model affects the deduced reaction critical energy by more than 2 kcal mol−1, however, which shows the importance of energy transfer in determining thermochemistry from unimolecular reaction fall-off data. It is shown that a single set of Arrhenius parameters gives a good fit of all the low temperature data and the shock-tube data extrapolated to the high pressure limit, obviating the need to invoke a change in reaction mechanism from concerted to diradical for high temperature conditions. Some possible future experiments are suggested. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    s.l. : American Chemical Society
    The @journal of physical chemistry 〈Washington, DC〉 99 (1995), S. 11867-11874 
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology , Physics
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 105 (1996), S. 1420-1425 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The time-resolved infrared fluorescence (IRF) technique has been used to study the vibrational deactivation of excited N2O by large polyatomic colliders at ambient temperature (295±2 K). N2O(0001) molecules were prepared by direct pumping with the P(18) line of a pulsed CO2 laser at 9.536 μm. The bimolecular rate constant for self-deactivation was determined to be (0.763±0.006)×103 Torr−1 s−1, in very good agreement with previous work. The rate constants for deactivation by Ar and H2 were found to be (0.103±0.003) and (4.89±0.52)×103 Torr−1 s−1, respectively. The deactivation rate constants for the large polyatomic molecules, c-C6H10, c-C6H12, C6H6, C6D6, C7H8, C7D8, C6H5F, p-C6H4F2, C6HF5 and C6F6, were found to be (176±10), (153±22), (115±4), (201±2), (127±11), (407±52), (144±14), (173±13), (129±8), and (48±9)×103 Torr−1 s−1, respectively. Experimental deactivation probabilities and average energies removed per collision are calculated and compared. There is little difference in deactivation probabilities between the acyclic ring compounds and their aromatic analogues and the partially-fluorinated benzenes but the perfluorinated compound, C6F6 is much less efficient than the other species. The perdeuterated species, C6D6 and C7D8, especially the latter, show enhanced deactivation relative to the other species, probably as a result of near-resonant intermolecular V–V energy transfer. The results are compared with our recent work on the deactivation of CO2(0001) by the same group of large polyatomic colliders [K. L. Poel, Z. T. Alwahabi, and K. D. King, Chem. Phys. 201, 263 (1995)]. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    International Journal of Chemical Kinetics 27 (1995), S. 623-626 
    ISSN: 0538-8066
    Keywords: Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The technique of laser flash photolysis/laser absorption has been used to obtain an absolute removal rate constant of (3.85 ± 0.18) × 10-10 cm3 molecule-1 s-1 for singlet methylene, 1CH2 (ã1A1), with germane (GeH4) at ambient temperature. The removal rate constant is compared with the values for methane (CH4) and silane (SiH4) which have been determined previously. © 1995 John Wiley & Sons, Inc.
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
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