The non-statistical dynamics of the {sup 18}O + {sup 32}O{sub 2} isotope exchange reaction at two energies
- Department of Chemistry, University of California, Berkeley, California 94720 (United States)
- Department of Mathematics, San José State University, San Jose, California 95192 (United States)
- Department of Chemistry and Chemical Biology, University of New Mexico, Albuquerque, New Mexico 87131 (United States)
- Institute for Materials and Environmental Chemistry, Research Centre for Natural Sciences, Hungarian Academy of Sciences, P.O.B. 286, Budapest H-1519 (Hungary)
- Institute of Atomic and Molecular Sciences, Academia Sinica, Taipei 10617, Taiwan (China)
The dynamics of the {sup 18}O({sup 3}P) + {sup 32}O{sub 2} isotope exchange reaction were studied using crossed atomic and molecular beams at collision energies (E{sub 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 O{sub 3}(X{sup 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{sub coll}. Comparisons with the QS calculations suggest that {sup 34}O{sub 2} is produced with a non-statistical rovibrational distribution that is hotter than predicted, and the discrepancy is larger at the lower E{sub 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 O{sub 3}(X{sup 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 O{sub 3}{sup *} 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.
- OSTI ID:
- 22420028
- Journal Information:
- Journal of Chemical Physics, Vol. 141, Issue 6; Other Information: (c) 2014 AIP Publishing LLC; Country of input: International Atomic Energy Agency (IAEA); ISSN 0021-9606
- Country of Publication:
- United States
- Language:
- English
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