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Computational Comparison of Different Reagent Ions in the Chemical Ionization of Oxidized Multifunctional Compounds

Hyttinen, Noora and Otkjær, Rasmus V. and Iyer, Siddharth and Kjaergaard, Henrik G. and Rissanen, Matti P. and Wennberg, Paul O. and Kurtén, Theo (2018) Computational Comparison of Different Reagent Ions in the Chemical Ionization of Oxidized Multifunctional Compounds. Journal of Physical Chemistry A, 122 (1). pp. 269-279. ISSN 1089-5639. doi:10.1021/acs.jpca.7b10015.

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High pressure anion chemical ionization is commonly used for the detection of neutral molecules in the gas phase. The detection efficiency in these measurements depends on how strongly the reagent ion binds to the neutral target molecule. We have calculated the binding strength of nitrate (NO_3–), acetate (CH_3C(O)O–), lactate (CH_3CH(OH)C(O)O–), trifluoroacetate (CF_3C(O)O–), trifluoromethanolate (CF_3O–), bromide (Br–) and iodide (I–) reagent ions to ten different products derived from the OH radical initiated oxidation of butadiene. We found that the binding of these oxidation products to the reagent ions depends almost linearly on the number of oxygen atoms in the target molecule, with the precise chemical identity of the compound (e.g. the number and relative position of hydroxyl or hydroperoxy groups) playing a more minor role. For acetate, the formation free energy decreases on average by around 4 kcal/mol when the number of oxygen atoms in the sample molecule increases by one. For the other reagent ions the corresponding decrease is around 3 kcal/mol. For all of the molecules studied, acetate forms the most stable clusters and I– the least stable. We also investigated the effect of humidity on the chemical ionization by calculating how strongly water molecules bind to both the reagent ions and the ion-molecule clusters. Water binds much more strongly to the reagent ion monomers compared to the reagent ion “dimers” (defined here as a cluster of the reagent anion with the corresponding neutral conjugate acid, e.g. HNO_3(NO_3–)) or the ion-molecule clusters. This likely leads to a stronger humidity dependence when using reagent ions that are not able to form reagent ion dimers (such as CF_3C(O)O–, CF_3O–, Br– and I–).

Item Type:Article
Related URLs:
URLURL TypeDescription Information
Otkjær, Rasmus V.0000-0002-6094-1828
Kjaergaard, Henrik G.0000-0002-7275-8297
Rissanen, Matti P.0000-0003-0463-8098
Wennberg, Paul O.0000-0002-6126-3854
Kurtén, Theo0000-0002-6416-4931
Additional Information:© 2017 American Chemical Society. Publication Date (Web): December 4, 2017. We thank John Crounse for helpful discussions. We thank the Academy of Finland (Grants 266388 and 299574) for funding, and CSC-IT Center for Science in Espoo, Finland, and University of Copenhagen for computing time. POW thanks the University of Copenhagen for hosting his sabbatical and funding from NASA via grant NNX14AP46G-ACCDAM. Author Contributions: The manuscript was written through contributions of all authors. All authors have given approval to the final version of the manuscript. The authors declare no competing financial interest.
Funding AgencyGrant Number
Academy of Finland266388
Academy of Finland299574
Issue or Number:1
Record Number:CaltechAUTHORS:20171204-155636314
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Official Citation:Computational Comparison of Different Reagent Ions in the Chemical Ionization of Oxidized Multifunctional Compounds Noora Hyttinen, Rasmus V. Otkjær, Siddharth Iyer, Henrik G. Kjaergaard, Matti P. Rissanen, Paul O. Wennberg, and Theo Kurtén The Journal of Physical Chemistry A 2018 122 (1), 269-279 DOI: 10.1021/acs.jpca.7b10015
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:83676
Deposited By: Tony Diaz
Deposited On:08 Dec 2017 03:42
Last Modified:15 Nov 2021 20:13

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