An experimental and computational study of the unimolecular-decay reaction of diethyl-substituted Criegee intermediate (CH)COO

• Published in: Physical chemistry chemical physics : PCCP 2024-11, Vol.26 (44), p.28244-28258
• Main Authors: Peltola, Jari, Pekkanen, Timo T, Heinonen, Petri, Salomaa, Pyry, Runeberg, Nino, Lendvay, György, Eskola, Arkke J
• Format: Article
• ISSN: 1463-9076; 1463-9084
• DOI: 10.1039/d4cp03620d

We have performed direct kinetic measurements to determine the thermal unimolecular-decay rate coefficient of (C 2 H 5 ) 2 COO as a function of temperature (223-296 K) and pressure (4-100 torr) using time-resolved UV-absorption spectroscopy. The stabilised (C 2 H 5 ) 2 COO Criegee intermediate was produced by photolysing 3-bromo-3-iodopentane ((C 2 H 5 ) 2 CIBr) with 213 nm radiation in the presence of O 2 . We performed quantum-chemistry calculations and master-equation simulations to complement the experimental work. At 296 K and 100 torr, we measure 1530 ± 440 s −1 (2 σ ) for the unimolecular-decay rate coefficient, and both the experiments and simulations indicate that the reaction is effectively at the high-pressure limit under these conditions. Key parameters in the master-equation model were optimised using the experimental results, and phenomenological rate coefficients were then computed to facilitate the use of the present results in modelling. A roaming channel that forms ( R / S )-2-hydroxypentan-3-one was included in the master-equation model. We also performed similar calculations for the unimolecular-decay reaction of (CH 3 ) 2 COO to improve the kinetic modelling of our previous work [J. Peltola et al. , Phys. Chem. Chem. Phys. , 2022, 24 , 5211-5219]. We have investigated unimolecular reaction kinetics of the diethyl-substituted Criegee intermediate, pentan-3-oneoxide, both experimentally and computationally.