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Dissociation, Relaxation, and Incubation in the Pyrolysis of Neopentane:  Heat of Formation for tert-Butyl Radical

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العنوان: Dissociation, Relaxation, and Incubation in the Pyrolysis of Neopentane:  Heat of Formation for tert-Butyl Radical
المؤلفون: Srinivasan, N. K., Kiefer, J. H., Tranter, R. S.
المصدر: The Journal of Physical Chemistry - Part A; March 2003, Vol. 107 Issue: 10 p1532-1539, 8p
مستخلص: Rate processes in neopentane−krypton mixtures were examined at high temperatures and over a very wide range of pressure in a shock tube using the laser−schlieren technique. The experiments used mixtures of 2, 5, 10, 20, and 30% in Kr and covered 600−2000 K for postshock pressures of 7−400 Torr. The combination of high temperature and low pressure made possible the observation of strong unimolecular falloff of the dissociation even in this large molecule and the full parametrization of a restricted rotor Gorin model RRKM fit. The choice of restriction parameter η and the average energy transfer 〈ΔE〉down both seem normal. The resulting k∞ is very close to earlier work that closely represents the high-pressure limit. When combined with other well-known thermochemistry, the barrier estimated from the RRKM extrapolation is 86 kcal/mol and this translates to a heat of formation of 12.8 kcal/mol for tert-butyl radical. All aspects of the decomposition are much as expected, and the results are almost routine except for the quite surprising observation of vibrational relaxation in the 25 Torr experiments. The process is fast, with Pτ < 100 ns atm, but this is still much slower than the room temperature ultrasonic data, which have Pτ ~ 4 ns atm. However, the strong slowing with temperature is easily ascribed to the need to transfer much larger amounts of energy for equilibration at high temperature but with an energy transfer rate already so rapid that it cannot increase much. The relaxation introduces an incubation delay that is quite useful in the modeling of the lowest pressure gradient profiles.
قاعدة البيانات: Supplemental Index
الوصف
تدمد:10895639
15205215