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The Photochemistry of Formaldehyde: Internal Conversion and Molecular Dissociation in a Single Step?

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posted on 21.08.2008 by Marta Araujo, Benjamin Lasorne, Michael J. Bearpark, Michael A. Robb
A novel, nonadiabatic reaction path for H2 + CO molecular dissociation of formaldehyde via an extended S1/S0 conical intersection seam has been mapped out using the CAS-SCF method with a full valence active space (10 electrons, 9 orbitals). Two conical intersection geometries have been optimized, CsCoIn, a saddle point in the intersection space, and C1CoIn, which is the lowest-energy crossing point. A minimum-energy path connecting these points along a seam has also been characterized. In addition to the conventional and “roaming-atom” mechanismswhere internal conversion takes place before ground-state dissociationwe suggest that a strictly nonadiabatic mechanism can operate, where internal conversion and dissociation take place in concert.