Theoretical and experimental studies of the diketene system: Product branching decomposition rate constants and energetics of isomers

The kinetics and mechanism for the thermal decomposition of diketene have been studied in the temperature range 510-603 K using highly diluted mixtures with Ar as a diluent. The concentrations of diketene, ketene, and CO₂ were measured by FTIR spectrometry using calibrated standard mixtures. Two reaction channels were identified. The rate constants for the formation of ketene (k₁) and CO₂ (k₂) have been determined and compared with the values predicted by the Rice-Ramsperger-Kassel-Marcus (RRKM) theory for the branching reaction. The first-order rate constants, k ₁ (s^-1)= 10^15.74±0.72 exp(-49.29 (kcal mol^-1) (±1.84)/RT) and k₂ (s^-1)= 10 ^14.65±0.87 exp(-49.01 (kcal mol^-1) (±2.22)/RT); the bulk of experimental data agree well with predicted results. The heats of formation of ketene, diketene, cyciobuta-1,3dione, and cyclobuta-1,2-dione at 298 K computed from the G2M scheme are -11.1, -45.3, -43,6, and -40,3 kcal mol^-1, respectively.