A new feature in the internal heavy isotope distribution in ozone
- Research Center for Environmental Changes, Academia Sinica, Taipei, Taiwan (China)
- Laboratoire de Glaciologie et Géophysique de l’Environnement, CNRS, Université Joseph Fourier-Grenoble, 54 rue Molière BP96, St Martin d’Heres, 38402 (France)
- Department of Earth and Atmospheric Sciences, Purdue University, Indiana 47906 (United States)
Ozone produced by discharge or photolysis of oxygen has unusually heavy isotopic composition ({sup 18}O/{sup 16}O and {sup 17}O/{sup 16}O ratio) which does not follow normal mass fractionation rule: δ{sup 17}O ∼ 0.52{sup *}δ{sup 18}O, expressed as an anomaly Δ{sup 17}O = δ{sup 17}O − 0.52{sup *}δ{sup 18}O. Ozone molecule being an open isosceles triangle can have the heavy isotope located either in its apex or symmetric (s) position or the base or asymmetric (as) position. Correspondingly, one can define positional isotopic enrichment, written as δ{sup 18}O (s) or δ{sup 18}O (as) (and similarly for δ{sup 17}O) as well as position dependent isotope anomaly Δ{sup 17}O (s) and Δ{sup 17}O (as). Marcus and co-workers have proposed a semi-empirical model based in principle on the RRKM model of uni-molecular dissociation but with slight modification (departure from statistical randomness assumption for symmetrical molecules) which explains many features of ozone isotopic enrichment. This model predicts that the bulk isotope anomaly is contained wholly in the asymmetric position and the Δ{sup 17}O (s) is zero. Consequently, Δ{sup 17}O (as) = 1.5 {sup *} Δ{sup 17}O (bulk) (named here simply as the “1.5 rule”) which has been experimentally confirmed over a range of isotopic enrichment. We now show that a critical re-analysis of the earlier experimental data demonstrates a small but significant departure from this 1.5 rule at the highest and lowest levels of enrichments. This departure provides the first experimental proof that the dynamics of ozone formation differs from a statistical model constrained only by restriction of symmetry. We speculate over some possible causes for the departure.
- OSTI ID:
- 22436549
- Journal Information:
- Journal of Chemical Physics, Vol. 141, Issue 13; 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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