Computed Pre-reactive Complex Association Lifetimes Explain Trends in Experimental Reaction Rates for Peroxy Radical Recombinations

The lifetimes of
pre-reactive complexes, although implicitly part
of the equations used to model many gas-phase bimolecular reactions,
have seldom been included in quantitative calculations of rate coefficients.
Here, we demonstrate the application of empirical molecular dynamics
simulations of collisions between peroxy radicals to model association
lifetimes. With the exception of the methyl peroxy–acetyl peroxy
system, measurements of the lifetimes based on a phenomenological
model are shown to correlate well with available experimental data
for recombination reactions of peroxy radicals in cases where the
rate-limiting transition state lies below the reactants in energy.
Further, we predict reaction rates for larger α-pinene-derived
peroxy radicals, and we interpret our results in tandem with available
experimental data on these systems, which are of great relevance to
improve our understanding of atmospheric aerosol formation.