10.1021/jp803152g.s008 Marta Araujo Marta Araujo Benjamin Lasorne Benjamin Lasorne Michael J. Bearpark Michael J. Bearpark Michael A. Robb Michael A. Robb The Photochemistry of Formaldehyde: Internal Conversion and Molecular Dissociation in a Single Step? American Chemical Society 2008 intersection space C 1CoIn seam saddle point conical intersection geometries conversion dissociation nonadiabatic reaction path CO Molecular Dissociation Internal Conversion 9 orbitals H 2 nonadiabatic mechanism 2008-08-21 00:00:00 Media https://acs.figshare.com/articles/media/The_Photochemistry_of_Formaldehyde_Internal_Conversion_and_Molecular_Dissociation_in_a_Single_Step_/2919217 A novel, nonadiabatic reaction path for H<sub>2</sub> + CO molecular dissociation of formaldehyde via an extended S<sub>1</sub>/S<sub>0</sub> 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.