Isoprene is the most abundant unsaturated hydrocarbon in the atmosphere. Ozonolysis of isoprene produces methyl vinyl ketone oxide (MVKO), which may react with atmospheric SO, formic acid, and other important species at substantial levels. In this study, we utilized ultraviolet absorption to monitor the unimolecular decay kinetics of -MVKO in real time at 278-319 K and 100-503 Torr. After removing the contributions of radical reactions and wall loss, the unimolecular decay rate coefficient of -MVKO was measured to be = 70 ± 15 s (1σ uncertainty) at 298 K with negligible pressure dependence. In addition, increases from ca. 30 s at 278 K to ca. 175 s at 319 K with an effective Arrhenius activation energy of 8.3 ± 2.5 kcal mol, () = (9.3 × 10)exp(-4200/) s. Our results indicate that unimolecular decay is the major sink of MVKO in the troposphere. The data would improve the estimation for the steady-state concentrations of MVKO and thus its oxidizing ability.
Download full-text PDF |
Source |
|---|---|
| http://dx.doi.org/10.1021/acs.jpca.0c07928 | DOI Listing |
Publication Analysis
Top Keywords
Similar Publications
Semiclassical Transition State Theory (SCTST) Rate Coefficients for the Unimolecular Decomposition of the Ethoxy (CHCHO) Radical.
J Phys Chem A
November 2024
Quantum Theory Project, Departments of Chemistry and Physics, University of Florida, Gainesville, Florida 32611, United States.
The thermal unimolecular decay of ethoxy is important in high-temperature combustion environments where the ethoxy radical is a key reactive intermediate. Two dissociation pathways of ethoxy, including the β-C-C scission to yield CH + CHO and the H-elimination to make H + CHCHO, were characterized using a high-level coupled-cluster-based composite quantum chemical method (mHEAT-345(Q)). The former route is found to be dominant while the latter is insignificant, in agreement with previous experimental and theoretical studies.
View Article and Find Full Text PDFAn experimental and computational study of the unimolecular-decay reaction of diethyl-substituted Criegee intermediate (CH)COO.
Phys Chem Chem Phys
November 2024
Department of Chemistry, University of Helsinki, P.O. Box 55 (A.I. Virtasen aukio 1), 00014 Helsinki, Finland.
We have performed direct kinetic measurements to determine the thermal unimolecular-decay rate coefficient of (CH)COO as a function of temperature (223-296 K) and pressure (4-100 torr) using time-resolved UV-absorption spectroscopy. The stabilised (CH)COO Criegee intermediate was produced by photolysing 3-bromo-3-iodopentane ((CH)CIBr) with 213 nm radiation in the presence of O. We performed quantum-chemistry calculations and master-equation simulations to complement the experimental work.
View Article and Find Full Text PDFInfrared Fingerprint and Unimolecular Decay Dynamics of the Hydroperoxyalkyl Intermediate (•QOOH) in Cyclopentane Oxidation.
J Phys Chem A
October 2024
Department of Chemistry, University of Pennsylvania, Philadelphia, Pennsylvania 19103-6323, United States.
A transient carbon-centered hydroperoxyalkyl intermediate (•QOOH) in the oxidation of cyclopentane is identified by IR action spectroscopy with time-resolved unimolecular decay to hydroxyl (OH) radical products that are detected by UV laser-induced fluorescence. Two nearly degenerate •QOOH isomers, β- and γ-QOOH, are generated by H atom abstraction of the cyclopentyl hydroperoxide precursor. Fundamental and first overtone OH stretch transitions and combination bands of •QOOH are observed and compared with anharmonic frequencies computed by second-order vibrational perturbation theory.
View Article and Find Full Text PDFBimolecular photodissociation of interstellar 1-Cyanonaphthalene via Intermolecular Coulombic decay.
J Chem Phys
September 2024
Indian Institute of Technology Madras, Chennai 600036, India.
Article Synopsis
- PAHs are common in space and play a crucial role in interstellar chemistry, with 1-CNN and 2-CNN being the first identified in the Taurus Molecular Cloud.
- At ambient light conditions similar to those in dense molecular clouds and planetary atmospheres, 1-CNN can fragment extensively due to a newly discovered mechanism.
- This fragmentation involves dimer formation and ionization processes that could lead to new cations, potentially influencing astrochemistry and the development of life in space.
The role of solar photolysis in the atmospheric removal of methacrolein oxide and the methacrolein oxide-water van-der Waals complex in pristine environments.
Photochem Photobiol
August 2024
University of Louisiana at Lafayette, Lafayette, Louisiana, USA.
Biogenic hydrocarbons are emitted into the Earth's atmosphere by terrestrial vegetation as by-products of photosynthesis. Isoprene is one such hydrocarbon and is the second most abundant volatile organic compound emitted into the atmosphere (after methane). Reaction with ozone represents an important atmospheric sink for isoprene removal, forming carbonyl oxides (Criegee intermediates) with extended conjugation.
View Article and Find Full Text PDFWant AI Summaries of new PubMed Abstracts delivered to your In-box?
Enter search terms and have AI summaries delivered each week - change queries or unsubscribe any time!