Inverse kinetic isotope effects in the charge transfer reactions of ammonia with rare gas ions

A. Tsikritea, K. Park, P. Bertier, J. Loreau, T. P. Softley, B. R. Heazlewood*

*Corresponding author for this work

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In the absence of experimental data, models of complex chemical environments rely on predicted reaction properties. Astrochemistry models, for example, typically adopt variants of capture theory to estimate the reactivity of ionic species present in interstellar environments. In this work, we examine astrochemically-relevant charge transfer reactions between two isotopologues of ammonia, NHand ND3, and two rare gas ions, Kr+and Ar+. An inverse kinetic isotope effect is observed; NDreacts faster than NH3. Combining these results with findings from an earlier study on Xe+(Petraliaet al.,Nat. Commun., 2020, 11, 1), we note that the magnitude of the kinetic isotope effect shows a dependence on the identity of the rare gas ion. Capture theory models consistently overestimate the reaction rate coefficients and cannot account for the observed inverse kinetic isotope effects. In all three cases, the reactant and product potential energy surfaces, constructed from high-level ab initio calculations, do not exhibit any energetically-accessible crossing points. Aided by a one-dimensional quantum-mechanical model, we propose a possible explanation for the presence of inverse kinetic isotope effects in these charge transfer reaction systems.

Original languageEnglish
Pages (from-to)10005-10013
Number of pages9
JournalChemical Science
Issue number29
Early online date22 Jun 2021
Publication statusPublished - 7 Aug 2021

Bibliographical note

Funding Information:
B. R. H. and T. P. S. acknowledge funding provided by the EPSRC (projects EP/N004647/1 and EP/N032950/1). B. R. H. also acknowledges the ERC (Starting Grant project 948373) and the Royal Society (RGS\R2\192210) for funding. A. T. thanks the Clarendon Fund for providing her with a scholarship and acknowledges that this paper was supported by the Onassis Foundation, Scholarship ID: F ZP 055-1/2019-2020. J.L. acknowledges support from Internal Funds KU Leuven through grant STG-19-00313.

Publisher Copyright:
© The Royal Society of Chemistry 2021.

ASJC Scopus subject areas

  • General Chemistry


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