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Author Bhattacharya, S. K. ♦ Liang, Mao-Chang ♦ Savarino, Joel ♦ Michalski, G.
Source United States Department of Energy Office of Scientific and Technical Information
Content type Text
Language English
Subject Keyword INORGANIC, ORGANIC, PHYSICAL AND ANALYTICAL CHEMISTRY ♦ DISSOCIATION ♦ ENRICHMENT ♦ ISOTOPE RATIO ♦ MOLECULES ♦ OXYGEN ♦ OXYGEN 16 ♦ OXYGEN 17 ♦ OXYGEN 18 ♦ OZONE ♦ PHOTOLYSIS ♦ SYMMETRY
Abstract 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.
ISSN 00219606
Educational Use Research
Learning Resource Type Article
Publisher Date 2014-10-07
Publisher Place United States
Journal Journal of Chemical Physics
Volume Number 141
Issue Number 13


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