Ab initio dynamics of unimolecular decomposition of β-propiolactone and β-propiolactam

Highlights: • PESs were investigated with the accurate composite W1U method. • Kinetic behaviors were characterized using the deterministic/stochastic ME model. • Calculated numbers are in excellent agreement with scatter experimental data. • A detailed kinetic sub-mechanism was provided for 500–2000 K and 0.001–760 torr. Using the potential energy surface and molecular properties obtained at the accurate composite W1U method, time-resolved temperature- and pressure-dependent behaviors of the thermal decomposition of β-propiolactone and β-propiolactam (for 500–2000 K & 0.001–760 Torr) were charaterized using the integrated deterministic/stochastic model within the master equation/Rice–Ramsperger–Kassel–Marcus (ME/RRKM) framework. The integrated model helps to confidently explain and predict the different kinetic behaviors of the two similar-ring systems, which is consistent with experimental data, namely, β-propiolactone only decomposes to C₂H₄ + CO₂ while β-propiolactam can form both C₂H₄ + HNCO (main product) and CH₂CO + CH₂NH (minor product).