Mechanistic Insight and Intersystem Crossing Dynamics of the C(³P) + H₂CO/D₂CO Reaction

The reaction of atomic carbon, C-(P-3), withH(2)CO has been investigated using the direct dynamics trajectorysurfacehopping (DDTSH) method with Tully's fewest switches algorithm.The lowest lying ground triplet and single states are considered forthe dynamics study at a reagent collision energy of 8.0 kcal/mol.From the trajectory calculations, we observed that CH2 +CO and H + HCCO are the two major product channels for the title reaction.The insertion mechanism of the C-(P-3) + H(2)COreaction is rather complex and is followed by three distinct intermediateswith no entrance channel barrier to the reaction on the B3LYP/6-31G-(d,p)potential energy surfaces. The triplet insertion complexes are formedby three different approaches; "Sideways", "End-on"and "Head-on" attack of the triplet carbon atom towardH(2)CO molecule. Our dynamics calculations predict a newproduct channel (H + HCCO-(X (2)A '')) with acontribution of similar to 46% of the overall products formation viaketocarbene intermediate through "Head-on" approach.Despite the weak spin-orbit coupling (SOC) interactions, intersystemcrossing (ISC) via a ketocarbene intermediate has a small but significantcontribution, about 2.3%, for the CH2 + CO channel. Tounderstand the kinetic isotope effects on the reaction dynamics, wehave extended our study for the C-(P-3) + D(2)COreaction. It is seen that isotopic substitution of both the H atomshas a small reduction in the extent of ISC dynamics for the carbeneformation. Our results, certainly, reveal the importance of the ketocarbeneintermediate and the H + HCCO products channel as one of the majorproduct formation channels in the title reaction, which was not reportedearlier.