Computational Investigation on the Formation and Decomposition Reactions of the C₄H₃O Compound

Gas-phase mechanism and kinetics of the formation and decomposition reactions of the C₄H₃O compound, a crucial intermediate of the atmospheric and combustion chemistry, were investigated using ab initio molecular orbital theory and the very expensive coupled-cluster CCSD(T)/CBS(T,Q,5)//B3LYP/6-311++G(3df,2p) method together with transition state theory and Rice-Ramsperger-Kassel-Macus kinetic predictions. The potential energy surface established shows that the C₃H₃ + CO addition reaction has four main entrances in which C₃H₃ + CO → IS1- (CHCCH₂CO) is the most energetically favorable channel. The calculated results revealed that the bimolecular rate constants are positively dependent on both temperatures (T = 300-2000 K) and pressures (P = 1-76,000 Torr). Of these values, the k ₁ rate constant of the C₃H₃ + CO → IS1- addition channel is dominant over the 300-2000 K temperature range, increasing from 1.53 × 10^-20 to 1.04 × 10^-13 cm³ molecule^-1 s^-1 with the branching ratio reducing from 62% to 44%. The predicted unimolecular rate coefficients in the ranges of T = 300-2000 K and P = 1-76,000 Torr revealed that the intermediate products IS1- , IS1- , and IS2 are rather unstable and would rapidly decompose back to the reactants (C₃H₃ + CO), especially at high temperatures (T > 1000 K). The high-pressure limit rate constants for the C₄H₃O decomposition leading to products (C₃H₃ + CO), (CHCCHCO + H), and (CHCO + C₂H₂) have been found to be in excellent agreement with the available literature values proposed by Tian et al. (Combust. Flame, 2011, 158, 756-773) without any adjustment from the ab initio calculations. Therefore, the predicted temperature- and pressure-dependent rate constants can be confidently used for modeling CO-related systems under atmospheric and combustion conditions.