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Mass-Independent Oxygen Isotope Fractionation in Selected Systems. Mechanistic Considerations

Marcus, R. A. (2008) Mass-Independent Oxygen Isotope Fractionation in Selected Systems. Mechanistic Considerations. In: Applications of Theoretical Methods to Atmospheric Science. Advances in Quantum Chemistry. No.55. Elsevier , Boston, MA, pp. 5-19. ISBN 9780123743350.

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Studies of the mass-independent effect on oxygen isotope fractionation (MIF) are summarized, focusing on the MIF in ozone formation in the laboratory, a similar effect being found in the atmosphere. (As used here the MIF for O isotopomers means that the usual three-isotope plot has a slope of about unity instead of the conventional 0.52.) The marked difference of results obtained with systems when there is extensive isotopic exchange (“scrambled”) and experimental conditions where isotopic exchange is minimized (“unscrambled”) is also discussed. Ratios of rate constants can be measured only in the latter and show large isotope effects. These large isotope effects were shown to cancel exactly when there is extensive isotopic exchange, and one then obtains instead an MIF for ozone. We also consider a possible role of the chaperon versus energy transfer mechanisms for ozone formation in influencing the temperature dependence of the MIF. MIF in other systems are noted. Separately we consider the CO+OH→CO_2 reaction, an isotopically anomalous reaction. It has sometimes been called “mass-independent” but has no O atom symmetry for the HOCO∗ intermediate and so no MIF in the above sense (ca. unit slope) would be expected on theoretical grounds.

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Marcus, R. A.0000-0001-6547-1469
Additional Information:© 2008 Elsevier Inc. Available online 26 April 2008. It is a pleasure to acknowledge the support of this research by the National Science Foundation and the very helpful comments of anonymous reviewers.
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Series Name:Advances in Quantum Chemistry
Issue or Number:55
Record Number:CaltechAUTHORS:20150317-103239277
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Official Citation:R.A. Marcus, Chapter 2 - Mass-Independent Oxygen Isotope Fractionation in Selected Systems. Mechanistic Considerations, In: Michael E. Goodsite and Matthew S. Johnson, Editor(s), Advances in Quantum Chemistry, Academic Press, 2008, Volume 55, Pages 5-19, ISSN 0065-3276, ISBN 9780123743350, (
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:55850
Deposited By: Tony Diaz
Deposited On:17 Mar 2015 17:41
Last Modified:10 Nov 2021 20:51

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