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oai:figshare.com:article/34045573 2026-10-01T12:06:24Z category_1 category_4 category_14 category_15 category_16 category_873 category_45 category_132 portal_63 item_type_6 month_year_10_2026

Determination of Channel-Specific Unimolecular Reaction Rate Coefficients of Peroxy Radicals Formed from the OH-Initiated Oxidation of α‑Pinene Qingwen Tao (5116427) Jonathan G. Varelas (13822079) Vili-Taneli Salo (7023356) John D. Crounse (1301634) Paul O. Wennberg (1298556) Franz M. Geiger (1338786) Regan J. Thomson (1368753) Henrik G. Kjaergaard (1298550) Lu Xu (386491) Biophysics Biochemistry Molecular Biology Neuroscience Physiology Chemical Sciences not elsewhere classified Sociology Infectious Diseases volatile organic compounds organic peroxy radicals constrain product distributions specific rate coefficients different atmospheric conditions different oxidation products peroxy radicals formed 2 </ sub competing unimolecular channels 7 − 0 5 − 0 0 − 1 atmospheric oxidation specific deuterium unimolecular chemistry initiated oxidation theoretical calculations quantitative basis obtain 0 experimental benchmarks employ site deuterated isotopologue channels lead central role Unimolecular reactions of organic peroxy radicals (RO₂) play a central role in the atmospheric oxidation of volatile organic compounds (VOCs), yet experimental constraints on their reaction kinetics remain limited. Ring-opened RO₂ formed in the OH-initiated oxidation of α-pinene undergoes rapid unimolecular reactions, including 1,5 H-shift, 1,6 H-shift, and endocyclization. However, previously reported experimental rate coefficients represent the overall unimolecular reaction rate from all channels and do not resolve branching among chemically distinct channels. As these channels lead to different oxidation products, channel-specific rate coefficients are needed to constrain product distributions under different atmospheric conditions. Here, we employ site-specific deuterium-labeled α-pinene isotopologues to selectively suppress individual H-shift channels and isolate the contributions of competing unimolecular channels. For each deuterated isotopologue, the overall unimolecular rate coefficient of the ring-opened RO₂ was determined at 296 K using hydroxy nitrate (HN)-based kinetic analysis and compared with that of unlabeled α-pinene to derive channel-specific rate coefficients. We obtain 0.7−0.4+0.5 s^–1 for the 1,6 H-shift, 0.5−0.3+0.5 s^–1 for the 1,5 H-shift, and 3.0−1.6+1.7 s^–1 for endocyclization. These values are consistent with theoretical calculations and provide direct experimental constraints on individual channel rate coefficients in α-pinene-derived RO₂ unimolecular chemistry. These channel-specific rate coefficients provide a quantitative basis for predicting oxidation product distributions under different atmospheric conditions and serve as experimental benchmarks for theoretical calculations of RO₂ unimolecular chemistry. 2026-10-01T00:00:00Z Text Journal contribution 10.1021/acsenvironau.6c00228.s001 https://figshare.com/articles/journal_contribution/Determination_of_Channel-Specific_Unimolecular_Reaction_Rate_Coefficients_of_Peroxy_Radicals_Formed_from_the_OH-Initiated_Oxidation_of_Pinene/34045573 CC BY-NC 4.0