Kinetic Isotope Effect of the ¹⁶O+³⁶O₂ and ¹⁸O+³²O₂ Isotope Exchange Reactions: Dominant Role of Reactive Resonances Revealed by an Accurate Time-Dependent Quantum Wavepacket Study
The O + O2 isotope exchange reactions play an important role in determining the oxygen isotopic composition of a number of trace gases in the atmosphere, and their temperature dependence and kinetic isotope effects (KIEs) provide important constraints on our understanding of the origin and mechanism of these and other unusual oxygen KIEs important in the atmosphere. This work reports a quantum dynamics study of the title reactions on the newly constructed Dawes-Lolur-Li-Jiang-Guo (DLLJG) potential energy surface (PES). The thermal reaction rate coefficients of both the 18O + 32O2 and 16O + 36O2 reactions obtained using the DLLJG PES exhibit a clear negative temperature dependence, in sharp contrast with the positive temperature dependence obtained using the earlier modified Siebert-Schinke-Bittererova (mSSB) PES. In addition, the calculated KIE shows an improved agreement with the experiment. These results strongly support the absence of the "reef" structure in the entrance/exit channels of the DLLJG PES, which is present in the mSSB PES. The quantum dynamics results on both PESs attribute the marked KIE to strong near-threshold reactive resonances, presumably stemming from the mass differences and/or zero point energy difference between the diatomic reactant and product. The accurate characterization of the reactivity for these near-thermoneutral reactions immediately above the reaction threshold is important for correct characterization of the thermal reaction rate coefficients.
Z. Sun et al., "Kinetic Isotope Effect of the ¹⁶O+³⁶O₂ and ¹⁸O+³²O₂ Isotope Exchange Reactions: Dominant Role of Reactive Resonances Revealed by an Accurate Time-Dependent Quantum Wavepacket Study," Journal of Chemical Physics, vol. 142, no. 17, American Institute of Physics (AIP), May 2015.
The definitive version is available at https://doi.org/10.1063/1.4919861
Center for High Performance Computing Research
Keywords and Phrases
Atmospheric temperature; Carrier mobility; Chemical reactions; Dynamics; Isotopes; Oxygen; Potential energy; Quantum chemistry; Quantum theory; Reaction rates; Temperature distribution; Isotope exchange reactions; Kinetic isotope effects; Negative temperatures; Oxygen isotopic composition; Quantum wave packets; Reaction thresholds; Temperature dependence; Thermal reaction rates; Potential energy surfaces
International Standard Serial Number (ISSN)
Article - Journal
© 2015 American Institute of Physics (AIP), All rights reserved.
01 May 2015