Investigation of Gas-Phase Reaction Kinetics between the Criegee Intermediate (CH <b> ₂ </b> OO) and Isobutylamine Using Cavity Ring-Down Spectroscopy and Computational Methods

The temperature-dependent gas-phase kinetics of the simplest Criegee intermediate (CH2OO) with isobutyl amine (IBA) have been investigated experimentally using Cavity Ring-down Spectroscopy. The rate coefficients were determined within a pseudo-first-order regime, where the IBA was present at a concentration of (2.26–11.32) × 1015 molecules cm–3, which is 3 orders of magnitude higher than the concentration of CH2OO (∼4.2 × 1012) molecules cm–3. At 298 K, a bimolecular rate coefficient of (6.99 ± 0.18) × 10–12 cm3 molecule–1 s–1 was obtained for the reaction. Under the experimental conditions of 278–318 K and (50 ± 2) Torr pressure, an inverse temperature dependence was observed for the rate coefficients. The Arrhenius expression for the experimental result is given by kCH2OO+IBA(T)= (1.41 ± 0.48) × 10–12 exp {(471.15 ± 102.20)/T} cm3 molecule–1 s–1. The temperature and pressure dependence of the reaction were determined theoretically at the CCSD(T)-F12/cc-pVTZ-F12//B3LYP/6–311+G(2d,2p) level of theory using MESMER. The experimental results were found to be in good agreement with the theoretical results. The atmospheric relevance of the hydroperoxide adduct and the correlation between the rate coefficients and bond dissociation energies of the amines were also discussed in this study.