On the Model Dependence of Kinetic Shifts in Unimolecular Reactions: The Dissociation of the Cations of Benzene and n-Butylbenzene
AIR FORCE RESEARCH LAB HANSCOM AFB MA SPACE VEHICLES DIRECTORATE
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Statistical adiabatic channel modelclassical trajectory SACMCT calculations have been performed for transitional mode dynamics in the simple bond fission reactions of C6H6 -- C6H5 H and n-C6H5C4H9 -- C7H7 n-C3H7. Reduced-dimensionality model potentials have been designed that take advantage of ab initio results as far as available. Average anisotropy amplitudes of the potentials were fitted by comparison of calculated specific rate constants kE,J with measured values. The kinetic shifts of the calculated kE curves and the corresponding bond energies Esub-OJ0, derived as 3.90 0.05 eV for C6H6 and 1.78 or- 0.05 eV for n-C6H5C4H9, were in good agreement with literature values from thermochemical studies. Kinetic shifts from fixed tight activated complex Rice-Ramsperger-Kassel-Marcus RRKM theory, which also reproduces the measured kE, were larger than the present SACMCT results as well as earlier results from variational transition state theory for C6H6. The approach using RRKM theory was found to underestimate Esub-OJ0 by about 0.2-0.3 eV. A simplified SACMCT-based method is also proposed which circumvents the trajectory calculations and allows derivation of Esub-OJ0 on the basis of measured kE and which provides similar accuracy as the full SACMCT treatment.
- Organic Chemistry
- Physical Chemistry