Details

Autor(en) / Beteiligte

• Hansen, Anne S.
• Bhagde, Trisha
• Moore, Kevin B.
• Moberg, Daniel R.
• Jasper, Ahren W.
• Georgievskii, Yuri
• Vansco, Michael F.
• Klippenstein, Stephen J.
• Lester, Marsha I.

Titel

Watching a hydroperoxyalkyl radical (•QOOH) dissociate

Ist Teil von

• Science (American Association for the Advancement of Science), 2021-08, Vol.373 (6555), p.679-682

Ort / Verlag

Washington: The American Association for the Advancement of Science

Erscheinungsjahr

2021

Quelle

American Association for the Advancement of Science

Beschreibungen/Notizen

• Spectral fingerprint of stabilized •QOOH Carbon-centered radicals containing the hydroperoxy group, commonly denoted as •QOOH, are elusive but are among the most critical intermediate species for kinetic modeling of hydrocarbon oxidation in various atmospheric and combustion processes. Their direct experimental observation is a long-standing challenge, with only one successful previous attempt. Using a combination of infrared activation spectroscopy and an ultraviolet laser–induced fluorescence detection method, Hansen et al . directly characterized the vibrational structure of a •QOOH intermediate in isobutane oxidation, collisionally stabilized and isolated, and followed its dissociative evolution under infrared activation with time and energy resolution. High-level electronic structure calculations revealed an important role of heavy-atom tunneling in this process. —YS An elusive intermediate in hydrocarbon oxidation is jet-cooled and isolated and its dissociation characterized by IR and theory. 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.