A prototypical hydroperoxyalkyl radical (•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 •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 •QOOH intermediate—again increased by heavy-atom tunneling—which are required for global models of atmospheric and combustion chemistry.

一种典型的氢过氧烷基自由基 (•QOOH) 中间体，在挥发性有机化合物的氧化过程中短暂形成，通过其红外指纹和能量依赖的单分子衰变直接观察到羟基自由基和环醚产物。发现 • QOOH 单分子解离率在很宽的能量范围内的直接时域测量与使用过渡态势垒区域的最先进电子结构表征从理论上预测的结果一致。单分子衰变通过涉及沿反应途径的OO伸长和CCO角收缩的大量重原子隧穿而增强。