Posted: August 7, 2008 |
Clean 3-way split observed |
(Nanowerk News) In chemistry as in life, threesomes are not known to break up neatly.
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And while open-minded thinkers have insisted that clean three-way splits do happen, nobody had actually witnessed one – until now.
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A paper in the Aug. 8 issue of Science provides the first hard evidence for the simultaneous break-up of a molecule into three equal parts.
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Previous studies of so-called "concerted break-ups" had only suggested their existence, said co-author Anna Krylov, a theoretical chemist at the University of Southern California.
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"The experiments by our collaborators (at the University of California, San Diego) demonstrated that this mechanism is present, and our theory explained why and how it happens," she said.
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The breakthrough matters for two reasons. Concerted reactions have long been thought to play an important role in organic chemistry, and Krylov's theoretical model offers a framework for better understanding and perhaps manipulating such reactions.
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In addition, important phenomena in the atmosphere and in combustion involve three-body reactions. Ozone forms when three molecules come together at exactly the same time – an event no different in theory from a simultaneous split.
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Such events are relatively rare: Theory and experiment agree that in most cases a threesome will fall apart in steps, with one bond breaking before the next.
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"Why would it happen simultaneously?" Krylov asked rhetorically.
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But she and graduate student Vadim Mozhayskiy showed that if the electrons of the sym-triazine molecule are energized in a particular way, the whole flies apart into three identical and equally energetic parts.
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Unraveling the mechanism has become possible only through the combined efforts of theoreticians and experimentalists.
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Co-author Robert Continetti and his team at UCSD used electrical charges to energize molecules of sym-triazine to their breaking point. By separating the molecules in time and space, the researchers were able to identify the products from individual molecular events.
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In some cases, the three parts from a single molecule had exactly the same energy and reached detectors at the same time, indicating that a simultaneous three-way split had occurred.
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Even with this discovery, three-body reactions remain largely mysterious, Krylov said.
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"The gap in understanding of single-bond and multiple-bond breaking processes is just incredible."
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Krylov hopes to promote further work in the field through her iOpenShell Center, a USC-based institute supported by the National Science Foundation and created to foster collaborations between theoretical and experimental chemists.
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"The center provides a framework for these interactions," she said.
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