Watching a hydroperoxyalkyl radical (•QOOH) dissociate

A prototypical hydroperoxyalkyl radical (center dot QOOH) intermediate, transiently formed in the oxidation of volatile organic compounds, was directly observed through its infrared fingerprint and energy-dependent unimolecular decay to hydroxyl radical and cyclic ether products. Direct time-domain measurements of center dot QOOH unimolecular dissociation rates over a wide range of energies were found to be in accord with those predicted theoretically using state- of-the-art electronic structure characterizations of the transition state barrier region. Unimolecular decay was enhanced by substantial heavy-atom tunneling involving O-O elongation and C-C-O angle contraction along the reaction pathway. Master equation modeling yielded a fully a priori prediction of the pressure-dependent thermal unimolecular dissociation rates for the center dot QOOH intermediate-again increased by heavy- atom tunneling-which are required for global models of atmospheric and combustion chemistry.

Automated summary

The prototypical hydroperoxyalkyl radical (center dot QOOH) intermediate, formed transiently in the oxidation of volatile organic compounds, was directly observed through its infrared fingerprint and energy-dependent unimolecular decay. Direct time-domain measurements of the QOOH· unimolecular dissociation rates at a wide range of energies aligned with theoretical predictions. Unimolecular decay was enhanced by heavy-atom tunneling involving O-O elongation and C-C-O angle contraction.