Theoretical Study on the Chemical Kinetics of <i>tert</i> -Butyl Hydroperoxide Pyrolysis: A Combined Ab Initio and Master Equation Approach

<i>tert</i>-Butyl hydroperoxide (TBHP), an alkyl organic peroxide compound, serves as a key source of hydroxyl radicals in fuel oxidation studies and a potential fuel additive due to its weak O-O bond. Sensitivity analysis shows that O-O bond fission in TBHP (forming ȮH and t-C₄H₉Ȯ) dominates its decomposition kinetics, governing ignition delay and ȮH production. However, existing experimental rate coefficients of TBHP O-O fission are limited at low to medium temperatures and pressures of 0.5 to 3 atm, leading to about an order of magnitude difference of rate coefficient (obtained by extrapolation) in different mechanisms at high temperatures (>1000 K). In this study, the kinetics of the TBHP pyrolysis have been investigated by ab initio calculations. The potential energy surface is constructed at the CCSD(T)/aug-cc-pVTZ//M06-2X/aug-cc-pVDZ level of theory. Microcanonical variational transition state theory and Rice-Ramsperger-Kassel-Marcus/Master equation calculations were performed to obtain temperature- and pressure-dependent rate coefficients. Four additional reaction pathways, in which TBHP proceeded through four distinct transition states to different bimolecular product channels, were identified during the calculations. However, since the energy barriers of these pathways are significantly higher than those of the O-O fission, their contributions to TBHP pyrolysis kinetics are limited and can be ignored. The present calculations were incorporated into a kinetic model, and the results illustrate that the present calculations remarkably affect the model's performance in terms of predicting OH time history.