Journal of Organic & Inorganic Chemistry

Quantum rate coefficients for the O + O2 exchange reaction

Euroscicon Conference on Physical Chemistry and Analytical Separation Techniques
October 08-09, 2018 Amsterdam, Netherlands

Pascal Honvault and Gregoire Guillon

Laboratoire ICB- CNRS/Universite de Bourgogne Franche-Comte, France

Posters & Accepted Abstracts: J Org Inorg Chem

DOI: 10.21767/2472-1123-C6-018

Abstract

Molecular oxygen O2 is the most important molecule on earth’s atmosphere and stratospheric ozone O3 protects us from the UV radiation. The abundance of 16O being 99.8%, O2 and O3 exclusively formed from it are dominant, thereby giving a reference for any process involving oxygen. A strong enrichment of O3 (~10%) in both 18O and 17O (mass-independent fractionation-MIF) has been observed decades ago and was reproduced in laboratory experiments. Although this phenomenon remains globally unexplained, the three-body recombination O + O2 + M ΓΆΒ?Β?> O3 + M is believed to be the main process leading to this enrichment. At sufficiently low pressures, it can be partitioned into two steps: the formation of O3 in a highly excited rovibrational state, from reaction O + O2ΓΆΒ?Β?> O3* (step 1), and its subsequent stabilization by collision with an energy absorbing partner M (say N2), O3* + M ΓΆΒ?Β?> O3 + M (step 2). Thus, the efficiency of the exchange reaction O + O2 ΓΆΒ?Β?> O3* ΓΆΒ?Β?> O2 + O, involving O3* as an intermediate, is one of the key parameters to understand ozone formation. We have shown that this reaction, initiated by step 1, is very fast with three identical 16O atoms involved due to a quantum permutation symmetry effect. Consequently, it competes ferociously with step 2 described above, the latter becoming in this way much less effective. We have reproduced experimentally observed negative temperature dependence for this reaction rate constant when 18O is involved, along with other groups. We will sum up results of a computationally intensive full-quantum investigation of the dynamics of the 16O + 32O2, 18O + 32O2 and 17O + 32O2 processes supported by an accurate global potential energy surface for the O3 ground state. Our study based on a time independent quantum mechanical approach demonstrates that all approximate theoretical simulation techniques and calculations previously reported for this process result in considerable inaccuracies, especially because of the neglect of the quantum symmetries such as the nuclear spin symmetry due to the three (or two) identical atoms, 16O or 18O.

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