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

Abstract

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-cis (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 k1 rate constant of the C3H3 + CO → IS1-cis 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-cis, IS1-trans, 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.