A theoretical investigation of nitrooxyalkyl peroxy radicals from NO3-initiated oxidation of isoprene
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Density functional theory and ab initio molecular orbital calculations have been employed to determine the structures and energetics of the nitrooxyalkyl peroxy radicals arising from the NO3-initiated oxidation of isoprene. Geometry optimizations of the peroxy radicals are performed using density functional theory at the B3LYP/6-31G(d,p) level and single-point energies are computed using second-order Møller-Plesset perturbation theory and the coupled-cluster theory with single and double excitations including perturbative corrections for the triple excitations (CCSD(T)). The zero-point corrected energies of the nitrooxyalkyl peroxy radicals are 37-43 kcal mol-1 more stable than the separated NO3, O2 and isoprene reactants at the CCSD(T)/6-31G(d)+CF level. The rate constants for the addition of O2 to the NO3-isoprene adducts are calculated using the canonical variational transition state theory (CVTST), with an overall rate constant of 3.8×10-12 cm3 molecule-1 s-1. The results provide the isomeric branching ratios between eight nitrooxyalkyl peroxy radicals. © 2007 Elsevier Ltd. All rights reserved.
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