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Chemistry at the threshold: Unexpected products, unusual mechanisms, and generally weird things that happen near the energetic threshold for a reaction

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7 Author(s)
Maccarone, A.T. ; Sch. of Chem., Univ. of Sydney, Sydney, NSW, Australia ; Nauta, K. ; de Wit, G. ; Quinn, M.
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Reactions that occur near the energetic threshold can be very different to those where energy is in excess. In a series of experiments, we have used a narrow linewidth laser to provide a small organic molecule, acetaldehyde (CH3CHO), with a precise amount of energy, and used laser and imaging based techniques to probe the reaction products. In this paper I shall present three different examples of "weird chemistry" that happens at threshold: i) two fragments of acetaldehyde, CH3 and HCO almost separate but are trapped in their mutual van der Waals well. Here they orbit each other and produce different chemical products; ii) selectively deuterated acetaldehyde is observed to undergo facile and unexpected H/D exchange before the reaction is complete; and iii) as soon as there is enough energy to break more than one bond, this channel becomes dominant, but the mechanism for this dominance is as yet unexplained. Near-threshold chemistry is not an esoteric, narrow window, but one that is prevalent in chemistry more generally. Examples in atmospheric and combustion chemistry will be presented.

Published in:

Quantum Electronics Conference & Lasers and Electro-Optics (CLEO/IQEC/PACIFIC RIM), 2011

Date of Conference:

Aug. 28 2011-Sept. 1 2011