Unimolecular dissociation of glyoxal via a three-body fragmentation channel has been studied by direct classical trajectory calculations using Hartree–Fock (HF) and hybrid density functional methods (BH&HLYP, B3LYP) with split valence and polarized basis sets [HF/3-21G, BH&HLYP/6-311G(d,p) and B3LYP/6-311G(d,p)]. The transition state for C2H2O2→H2+2 CO has a dihedral angle of 90–110° between the carbonyl groups and a calculated barrier of ∼59 kcal/mol above the trans conformer. To simulate the experimental conditions, trajectories were started from a microcanonical ensemble at the transition state with 4, 8, and 16 kcal/mol excess energy distributed among the vibrational modes and the transition vector. In agreement with experiment, the CO rotational distribution is very broad with a high 〈J〉. However, the calculations yielded more CO vibrational excitation for the triple dissociation channel than observed for all channels combined. Hydrogen is produced with low J but significant vibrational excitation, in accord with experiment. Similar to trajectory studies on H2CO→H2+CO, there is a good correlation between the energy released along the part of the reaction path where most of the H2 bond length change occurs and the average vibrational excitation of the H2 products.

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