Automatization of Atmospheric OH Radical Abstraction Reactions

The gas-phase hydrogen abstraction reaction kinetics of atmospheric volatile organic compounds (VOCs) have been investigated using multiconformer transition state theory (MC-TST) as part of the development of the Jammy Key for Transition States (JKTS), an automated tool developed to address the vast number of organic species in the atmosphere that constantly undergo reactions with radicals. The rate constants for OH-initiated reactions with several short-chain compounds─methane, ethane, propane, and their corresponding alcohols and carbonyls─were computationally determined and compared to experimental data. Additionally, the OH abstraction kinetics of pinonaldehyde, a key oxidation product of biogenic VOCs, were studied in detail. Tunnelling effects were evaluated using Wigner and Eckart tunnelling corrections to ensure accurate prediction of reaction rates. JKTS yielded rate constants within a factor of ∼2-3 of experimental data across all systems studied, with branching ratios for pinonaldehyde showing significant contributions from aldehydic and tertiary hydrogen abstraction pathways. The calculated rate constants for pinonaldehyde, 1.739 × 10^-11 cm³ molecule^-1 s^-1 (Eckart) and 1.847 × 10^-11 cm³ molecule^-1 s^-1 (Wigner), align well with the experimental values of (4-9) × 10^-11 cm³ molecule^-1 s^-1 at room temperature. These results demonstrate the capability of JKTS to automate the computation of reaction kinetics and support its application in atmospheric chemistry for accurate modeling of VOC oxidation mechanisms.