Sivaramakrishnan, Raghu; Tao, Yujie; Georgievskii, Yuri; Klippenstein, Stephen; Miller, James
In prior studies from our laboratory we have shown that weakly-bound free radicals have a propensity to promptly dissociate at elevated temperatures relevant to flames. Dissociation can occur so rapidly at high temperatures in such weakly-bound radicals that it interferes with collisional relaxation of internal energies leading to prompt dissociation. While prompt dissociation is a ubiquitous feature in such free radical dissociations, we have hypothesizedthat its relevance to global combustion observables such as flame speeds depends on satisfying specific criteria. Two criteria that motivate the present study are that the free radicals must play a central role in the oxidation mechanism and that their thermal dissociation rate coefficients should be small enough. Resonance stabilized radicals have bond strengths ~ 50 kcal/mol (or larger) and consequently are known to dissociate slowly and persist even in hightemperature environments. In this work we have calculated prompt dissociation probabilities for some simple allylic (allyl, methyl allyl, and dimethyl allyl) radicals. Flame simulations were performed to quantify the relevance of including prompt dissociations of these allylic radicals.