Interception of excited vibrational quantum states by O2 in atmospheric association reactions |
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| Authors: | David R Glowacki James Lockhart Mark A Blitz Stephen J Klippenstein Michael J Pilling Struan H Robertson Paul W Seakins |
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| Institution: | School of Chemistry, University of Bristol, Bristol, UK. drglowacki@gmail.com |
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| 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. |
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