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Science. 2004 Nov 12;306(5699):1158-61. Epub 2004 Oct 21.

The roaming atom: straying from the reaction path in formaldehyde decomposition.

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  • 1Department of Chemistry, Stony Brook University, Stony Brook, NY 11794, USA.


We present a combined experimental and theoretical investigation of formaldehyde (H2CO) dissociation to H2 and CO at energies just above the threshold for competing H elimination. High-resolution state-resolved imaging measurements of the CO velocity distributions reveal two dissociation pathways. The first proceeds through a well-established transition state to produce rotationally excited CO and vibrationally cold H2. The second dissociation pathway yields rotationally cold CO in conjunction with highly vibrationally excited H2. Quasi-classical trajectory calculations performed on a global potential energy surface for H2CO suggest that this second channel represents an intramolecular hydrogen abstraction mechanism: One hydrogen atom explores large regions of the potential energy surface before bonding with the second H atom, bypassing the saddle point entirely.

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