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-onand 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.

Automated summary

The reaction of atomic carbon with H(2)CO was studied using the direct dynamics trajectory surface hopping method. CH2+CO and H+HCCO were observed to be the major product channels. The insertion mechanism of the reaction is complex, with three different intermediates formed. A new product channel (H+HCCO-(X (2)A '')) was predicted through a head-on approach, contributing to approximately 46% of the overall products.