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The influence of non-equilibrium transient effects on measurements of vibrational relaxation times and of dissociation rate constants

Teitelbaum, Heshel

Canadian journal of chemistry, 1982-12-01, Vol.60 (23), p.2927-2942 [Periódico revisado por pares]

Ottawa, Canada: NRC Research Press

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  • Título:
    The influence of non-equilibrium transient effects on measurements of vibrational relaxation times and of dissociation rate constants
  • Autor: Teitelbaum, Heshel
  • É parte de: Canadian journal of chemistry, 1982-12-01, Vol.60 (23), p.2927-2942
  • Descrição: A semi-empirical analysis based on a rate law for vibrational relaxation of dissociating simple harmonic oscillators allows for a detailed study of measurements of vibrational relaxation times τ and of steady dissociation rate coefficients k 0 . It is shown that non-equilibrium populations of vibrational energy levels prevent attainment of the thermodynamically expected equilibrium energy. Even under near-isothermal and mild conditions, , serious experimental errors result when the Bethe-Teller relaxation rate law is used. Closed form expressions are given which permit evaluation of these errors. Measurements should be analyzed using the rate law where is the vibrational energy per molecule, τ the relaxation time, k d the non-equilibrium rate coefficient, τ the thermodynamically expected vibrational energy at temperature T, and ( *  + hv) the energy just above the dissociation limit. It is also shown that if a local minimum and maximum are predicted for measured density gradients in shock tube dissociations of diatomic molecules, where t ine is the incubation time, D′ the effective dissociation energy, and x 0 the mole fraction of dissociating molecules in an inert diluent. Expressions are given for extracting incubation times and rate constants from such studies when . Analysis of experimental data actually showing such phenomena (J. Chem Phys. 55 , 4017 (1971)) is carried out. There are indications that any analysis which does not explicitly account for transient effects could result in errors in measured k 0 's of factors of 2 or more.
  • Editor: Ottawa, Canada: NRC Research Press
  • Idioma: Inglês;Francês

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