title: The non-statistical dynamics of the ¹⁸O + ³²O₂ isotope exchange reaction at two energies.
abstract: The dynamics of the (18)O((3)P) + (32)O2 isotope exchange reaction were studied using crossed atomic and molecular beams at collision energies (E(coll)) of 5.7 and 7.3 kcal/mol, and experimental results were compared with quantum statistical (QS) and quasi-classical trajectory (QCT) calculations on the O3(X(1)A') potential energy surface (PES) of Babikov et al. [D. Babikov, B. K. Kendrick, R. B. Walker, R. T. Pack, P. Fleurat-Lesard, and R. Schinke, J. Chem. Phys. 118, 6298 (2003)]. In both QS and QCT calculations, agreement with experiment was markedly improved by performing calculations with the experimental distribution of collision energies instead of fixed at the average collision energy. At both collision energies, the scattering displayed a forward bias, with a smaller bias at the lower E(coll). Comparisons with the QS calculations suggest that (34)O2 is produced with a non-statistical rovibrational distribution that is hotter than predicted, and the discrepancy is larger at the lower E(coll). If this underprediction of rovibrational excitation by the QS method is not due to PES errors and/or to non-adiabatic effects not included in the calculations, then this collision energy dependence is opposite to what might be expected based on collision complex lifetime arguments and opposite to that measured for the forward bias. While the QCT calculations captured the experimental product vibrational energy distribution better than the QS method, the QCT results underpredicted rotationally excited products, overpredicted forward-bias and predicted a trend in the strength of forward-bias with collision energy opposite to that measured, indicating that it does not completely capture the dynamic behavior measured in the experiment. Thus, these results further underscore the need for improvement in theoretical treatments of dynamics on the O3(X(1)A') PES and perhaps of the PES itself in order to better understand and predict non-statistical effects in this reaction and in the formation of ozone (in which the intermediate O3* complex is collisionally stabilized by a third body). The scattering data presented here at two different collision energies provide important benchmarks to guide these improvements.
authors.affiliation: Department of Chemistry, San José State University, San Jose, California 95192, USA.
authors.forename: Annalise L
authors.initials: AL
authors.lastname: Van Wyngarden
authors.affiliation: Department of Chemistry, University of California, Berkeley, California 94720, USA.
authors.forename: Kathleen A
authors.initials: KA
authors.lastname: Mar
authors.affiliation: Department of Mathematics, San José State University, San Jose, California 95192, USA.
authors.forename: Jim
authors.initials: J
authors.lastname: Quach
authors.affiliation: Department of Mathematics, San José State University, San Jose, California 95192, USA.
authors.forename: Anh P Q
authors.initials: AP
authors.lastname: Nguyen
authors.affiliation: Department of Chemistry, University of California, Berkeley, California 94720, USA.
authors.forename: Aaron A
authors.initials: AA
authors.lastname: Wiegel
authors.affiliation: Department of Chemistry and Chemical Biology, University of New Mexico, Albuquerque, New Mexico 87131, USA.
authors.forename: Shi-Ying
authors.initials: SY
authors.lastname: Lin
authors.affiliation: Institute for Materials and Environmental Chemistry, Research Centre for Natural Sciences, Hungarian Academy of Sciences, P.O.B. 286, Budapest H-1519, Hungary.
authors.forename: Gyorgy
authors.initials: G
authors.lastname: Lendvay
authors.affiliation: Department of Chemistry and Chemical Biology, University of New Mexico, Albuquerque, New Mexico 87131, USA.
authors.forename: Hua
authors.initials: H
authors.lastname: Guo
authors.affiliation: Institute of Atomic and Molecular Sciences, Academia Sinica, Taipei 10617, Taiwan.
authors.forename: Jim J
authors.initials: JJ
authors.lastname: Lin
authors.affiliation: Institute of Atomic and Molecular Sciences, Academia Sinica, Taipei 10617, Taiwan.
authors.forename: Yuan T
authors.initials: YT
authors.lastname: Lee
authors.affiliation: Department of Chemistry, University of California, Berkeley, California 94720, USA.
authors.forename: Kristie A
authors.initials: KA
authors.lastname: Boering