Direct generation of a prototypical n-pentyl peroxy radical reveals how mixedfate chemical regimes shape product distributions
- 1Chemistry and Biochemistry, University of California Los Angeles, 607 Charles E Young Dr E, Los Angeles, CA, United States, 90095
Abstract
Organic peroxy radicals (RO2) are key branch points in atmospheric oxidation with competing fates in the troposphere: reaction with NO, reaction with HO2, self-/cross-reaction with another RO2, and isomerization. RO2 often react in mixed-fate regimes, yielding product distributions with a complex dependence on reactivity conditions. In traditional environmental chamber experiments, not all RO2 fates are equally accessible, and chemical regimes favoring RO2 self-/cross-reactions and isomerizations are poorly characterized. Here, we access these conditions in an environmental chamber via 1-iodopentane photolysis, monitoring product distributions with NH4 + chemical ionization mass spectrometry. We tune the relative importance of these reaction pathways by varying the initial conditions, spanning bimolecular lifetimes from ~100-2000 s. Across conditions, the major observed C5 product, C5H10O3 (~40-60% yield), requires at least one RO2 isomerization to form, demonstrating the importance of downstream RO2 unimolecular reactions even if they are not the major fate of upstream RO2. Model mechanisms partially reproduce observed product distributions but cannot quantitatively capture variations with changing RO2 fate. Discrepancies suggest poorly-understood RO2 cross-reactions substantially influence product distributions. Conditions favoring RO2 isomerization unintuitively enhance both fragmentation and accretion via downstream functionalized alkoxy and peroxy radical chemistry. Results illuminate important gaps in existing atmospheric reaction mechanisms when predicting product distributions in mixed-fate chemical regimes.
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BibTeX
@misc{crabtree2026direct,
title = {{Direct generation of a prototypical n-pentyl peroxy radical reveals how mixedfate chemical regimes shape product distributions}},
author = {Cooper K. Crabtree and Sara E. Murphy and Victoria P. Barber},
howpublished = {ChemRxiv},
year = {2026},
month = sep,
doi = {10.26434/chemrxiv.15009256/v1},
url = {https://chemrxiv.org/doi/full/10.26434/chemrxiv.15009256/v1},
note = {CC BY},
}
RIS
TY - UNPB
TI - Direct generation of a prototypical n-pentyl peroxy radical reveals how mixedfate chemical regimes shape product distributions
AU - Cooper K. Crabtree
AU - Sara E. Murphy
AU - Victoria P. Barber
PY - 2026
DA - 2026/09/22
PB - ChemRxiv
DO - 10.26434/chemrxiv.15009256/v1
UR - https://chemrxiv.org/doi/full/10.26434/chemrxiv.15009256/v1
AB - Organic peroxy radicals (RO2) are key branch points in atmospheric oxidation with competing fates in the troposphere: reaction with NO, reaction with HO2, self-/cross-reaction with another RO2, and isomerization. RO2 often react in mixed-fate regimes, yielding product distributions with a complex dependence on reactivity conditions. In traditional environmental chamber experiments, not all RO2 fates are equally accessible, and chemical regimes favoring RO2 self-/cross-reactions and isomerizations are poorly characterized. Here, we access these conditions in an environmental chamber via 1-iodopentane photolysis, monitoring product distributions with NH4 + chemical ionization mass spectrometry. We tune the relative importance of these reaction pathways by varying the initial conditions, spanning bimolecular lifetimes from ~100-2000 s. Across conditions, the major observed C5 product, C5H10O3 (~40-60% yield), requires at least one RO2 isomerization to form, demonstrating the importance of downstream RO2 unimolecular reactions even if they are not the major fate of upstream RO2. Model mechanisms partially reproduce observed product distributions but cannot quantitatively capture variations with changing RO2 fate. Discrepancies suggest poorly-understood RO2 cross-reactions substantially influence product distributions. Conditions favoring RO2 isomerization unintuitively enhance both fragmentation and accretion via downstream functionalized alkoxy and peroxy radical chemistry. Results illuminate important gaps in existing atmospheric reaction mechanisms when predicting product distributions in mixed-fate chemical regimes.
ER -