Hydrogen-atom production channels of acetaldehyde photodissociation: Direct DFT molecular dynamics study

Direct density-functional (DFT) molecular dynamics (MD) calculations have been carried out for the following two hydrogen-atom production channels in acetaldehyde photodissociation on the lowest triplet-state (T₁) potential energy surface (PES): CD₃CHO → CD₂CHO + D (1) and CD₃CHO → CD₃CO + H (2). The employed DFT method was B3LYP with the cc-pVDZ basis set. The average product hydrogen kinetic energies estimated from the results of the direct DFT MD calculations were 18.3 and 16.6 kcal mol⁻¹ for reactions 1 and 2, respectively, and these were half – two thirds of the previously measured values [T.Y. Kang, S.W. Kang, H.L. Kim, Chem. Phys. Lett. 434 (2007) 6]. This is because of the low reverse barrier heights predicted at the B3LYP/cc-pVDZ level. The present results for the product hydrogen kinetic energies, however, agree qualitatively with the experimental measurements and strongly supports the mechanisms taking place on the T₁ PES.