A comprehensive study of the unimolecular dissociation of the radical on the ground doublet and excited quartet potential energy surfaces has been carried out with multireference single and double excitation configuration interaction and second-order multireference perturbation methods. Two forms of the radical have been located in the linear and cyclic region of the lowest doublet potential energy surface with an isomerization barrier of 62.2 kcal/mol above the linear Three equivalent minima of cyclic are connected by low barrier, meaning the molecule is free to undergo pseudorotation. The cyclic is metastable with respect to ground state products, and dissociation must occur via intersystem crossing to a quartet potential energy surface. Minima on the seams of crossing between the doublet and quartet potential surfaces are found to lie substantially higher in energy than the cyclic minima. This strongly suggests that cyclic possesses a long collision-free lifetime even if formed with substantial internal excitation.
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Research Article| December 14 2004
High-level ab initio studies of unimolecular dissociation of the ground-state radical
Peng Zhang, Keiji Morokuma, Alec M. Wodtke; High-level ab initio studies of unimolecular dissociation of the ground-state radical. J. Chem. Phys. 1 January 2005; 122 (1): 014106. https://doi.org/10.1063/1.1804497
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