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 CO 2 were measured by FTIR spectrometry using calibrated standard mixtures. Two reaction channels were identified. The rate constants for the formation of ketene ( k 1 ) and CO 2 ( k 2 ) 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 k 2 (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, cyclobuta‐1,3‐dione, 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. © 2007 Wiley Periodicals, Inc. Int J Chem Kinet 39: 580–590, 2007