title: Interception of excited vibrational quantum states by O2 in atmospheric association reactions.
abstract: Bimolecular reactions in Earth's atmosphere are generally assumed to proceed between reactants whose internal quantum states are fully thermally relaxed. Here, we highlight a dramatic role for vibrationally excited bimolecular reactants in the oxidation of acetylene. The reaction proceeds by preliminary adduct formation between the alkyne and OH radical, with subsequent O(2) addition. Using a detailed theoretical model, we show that the product-branching ratio is determined by the excited vibrational quantum-state distribution of the adduct at the moment it reacts with O(2). Experimentally, we found that under the simulated atmospheric conditions O(2) intercepts ~25% of the excited adducts before their vibrational quantum states have fully relaxed. Analogous interception of excited-state radicals by O(2) is likely common to a range of atmospheric reactions that proceed through peroxy complexes.
authors.affiliation: School of Chemistry, University of Bristol, Bristol, UK. drglowacki@gmail.com
authors.forename: David R
authors.initials: DR
authors.lastname: Glowacki
authors.forename: James
authors.initials: J
authors.lastname: Lockhart
authors.forename: Mark A
authors.initials: MA
authors.lastname: Blitz
authors.forename: Stephen J
authors.initials: SJ
authors.lastname: Klippenstein
authors.forename: Michael J
authors.initials: MJ
authors.lastname: Pilling
authors.forename: Struan H
authors.initials: SH
authors.lastname: Robertson
authors.forename: Paul W
authors.initials: PW
authors.lastname: Seakins
mesh_terms: D000114:Acetylene / Q000737:chemistry*; D001272:Atmosphere / Q000737:chemistry*; D008956:Models, Chemical; D010084:Oxidation-Reduction; D010100:Oxygen / Q000737:chemistry*; D011789:Quantum Theory; D014732:Vibration
chemical_list: D000114:Acetylene; D010100:Oxygen