Computational and Experimental Investigation of the Detection of HO2 Radical and the Products of Its Reaction with Cyclohexene Ozonolysis Derived RO2 Radicals by an Iodide-Based Chemical Ionization Mass Spectrometer

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Iyer , S , He , X , Hyttinen , N , Kurten , T & Rissanen , M P 2017 , ' Computational and Experimental Investigation of the Detection of HO2 Radical and the Products of Its Reaction with Cyclohexene Ozonolysis Derived RO2 Radicals by an Iodide-Based Chemical Ionization Mass Spectrometer ' , Journal of Physical Chemistry A , vol. 121 , no. 36 , pp. 6778-6789 . https://doi.org/10.1021/acs.jpca.7b01588

Title: Computational and Experimental Investigation of the Detection of HO2 Radical and the Products of Its Reaction with Cyclohexene Ozonolysis Derived RO2 Radicals by an Iodide-Based Chemical Ionization Mass Spectrometer
Author: Iyer, Siddharth; He, Xucheng; Hyttinen, Noora; Kurten, Theo; Rissanen, Matti P.
Contributor organization: Department of Chemistry
Department of Physics
Polar and arctic atmospheric research (PANDA)
Date: 2017-09-14
Language: eng
Number of pages: 12
Belongs to series: Journal of Physical Chemistry A
ISSN: 1089-5639
DOI: https://doi.org/10.1021/acs.jpca.7b01588
URI: http://hdl.handle.net/10138/307395
Abstract: The HO2 radical is an important atmospheric molecule that can potentially influence the termination of autoxidation processes of volatile organic compounds (VOCs) that lead to the formation of highly oxygenated multifunctional compounds (HOMs). In this work, we demonstrate the direct detection of the HO2 radical using an iodide-based chemical ionization mass spectrometer (iodide-CIMS). Expanding on the previously established correlation between molecule-iodide binding enthalpy and iodide-CIMS instrument sensitivity, the experimental detection of the HO2 radical was preceded by the quantum chemical calculation of the HO2*I- cluster (PBE/aug-cc-pVTZ-PP level), which showed a reasonably strong binding enthalpy of 21.60 kcal/mol. Cyclohexene ozonolysis intermediates and closed-shell products were next detected by the iodide-CIMS. The ozone-initiated cyclohexene oxidation mechanism was perturbed by the introduction of the HO2 radical, leading to the formation of closed-shell hydroperoxides. The experimental investigation once again followed the initial computational molecule-iodide binding enthalpy calculations. The quantum chemical calculations were performed at the PBE/aug-cc-pVTZ-PP level for radicals and DLPNO-CCSD(T)/def2-QZVPP//PBE/aug-cc-pVTZ-PP level for the closed-shell products. A comparison between the iodide-CIMS and nitrate-CIMS spectra with identical measurement steps revealed that the iodide-CIMS was able to detect the low-oxidized (O/C ratio 0.5 and 0.66) cyclohexene ozonolysis monomer products more efficiently than nitrate-CIMS. Higher-oxidized monomers (O/C ratio 1 to 1.5) were detected equally well by both methods. An investigation of dimers showed that both iodide- and nitrate-CIMS were able to detect the dimer compositions possibly formed from reactions between the peroxy radical monomers considered in this study. Additionally, iodide-CIMS detected organic ions that were formed by a previously suggested mechanism of dehydroxylation of peroxy acids (and deoxygenation of acyl peroxy radicals) by H2O*I- clusters. These mechanisms were computationally verified.
Subject: SECONDARY ORGANIC AEROSOL
GAS-PHASE OZONOLYSIS
PARTICLE FORMATION
PEROXY-RADICALS
TROPOSPHERE
ACID
PSEUDOPOTENTIALS
CHEMISTRY
ALKENES
SYSTEM
116 Chemical sciences
114 Physical sciences
Peer reviewed: Yes
Usage restriction: openAccess
Self-archived version: acceptedVersion


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