title: Tunneling effects in the unimolecular decay of (CH3)2COO Criegee intermediates to OH radical products.
abstract: Unimolecular decay of the dimethyl substituted Criegee intermediate (CH3)2COO is observed at energies significantly below the transition state barrier associated with hydrogen atom transfer [Y. Fang et al., J. Chem. Phys. 144, 061102 (2016)] with time-resolved detection of the resultant OH radical products. (CH3)2COO is prepared at specific energies in the 3900-4600 cm-1region through IR excitation of combination bands involving CH stretch and another lower frequency mode, and the OH products are detected by UV laser-induced fluorescence. OH appearance times on the order of microseconds are observed in this deep tunneling regime, which are about 100 times slower than that in the vicinity of the barrier. The experimental rates are in good accord with Rice-Ramsperger-Kassel-Marcus (RRKM) calculations of the microcanonical dissociation rates for (CH3)2COO that include tunneling. Master equation modeling based on these microcanonical rates is used to predict the thermal decay rate of (CH3)2COO to OH products under atmospheric conditions of 276 s-1at 298 K (high pressure limit). Thermal unimolecular decay of (CH3)2COO to OH products is shown to have significant contributions from tunneling at energies much below the barrier to H-atom transfer.
authors.affiliation: Department of Chemistry, University of Pennsylvania, Philadelphia, Pennsylvania 19104-6323, USA.
authors.forename: Yi
authors.identifier: 0000000349174311
authors.initials: Y
authors.lastname: Fang
authors.affiliation: Department of Chemistry, University of Pennsylvania, Philadelphia, Pennsylvania 19104-6323, USA.
authors.forename: Victoria P
authors.initials: VP
authors.lastname: Barber
authors.affiliation: Chemical Sciences and Engineering Division, Argonne National Laboratory, Argonne, Illinois 60439, USA.
authors.forename: Stephen J
authors.identifier: 0000000162979187
authors.initials: SJ
authors.lastname: Klippenstein
authors.affiliation: Department of Chemistry, University of Washington, Seattle, Washington 98195, USA.
authors.forename: Anne B
authors.identifier: 0000000168516634
authors.initials: AB
authors.lastname: McCoy
authors.affiliation: Department of Chemistry, University of Pennsylvania, Philadelphia, Pennsylvania 19104-6323, USA.
authors.forename: Marsha I
authors.identifier: 0000000323673497
authors.initials: MI
authors.lastname: Lester