The Quantum Dynamical Basis of a Classical Kinetic Scheme Describing Coherent and Incoherent Regimes of Radical Pair Recombination

Nikita N. Lukzen, Johannes H. Klein, Christoph Lambert, Ulrich E. Steiner

Research output: Contribution to journalArticlepeer-review

9 Citations (Scopus)

Abstract

In recent work from this group (J. H. Klein et al. J. Am. Chem. Soc. 2015, 137, 11011), the magnetic field dependent charge recombination kinetics in donor/Ir-complex/acceptor triads has been determined with outstanding accuracy and reproducibility. The field-dependent kinetics has been analyzed in terms of a classical reaction scheme including the field-independent rate parameters of singlet recombination (rate constant kS) and S/T0 mixing (rate constant kST0) and the field-dependent rate constant k±(B) connecting central and outer Zeeman levels. In the present work, the extraction of k± from the experimental data is more precisely defined and the appearance of a "coherent" and "incoherent" regime of spin motion in a double log plot of k± vs. B is confirmed. The experimental decay curves have been reproduced by a full quantum dynamical model based on the stochastic Liouville equation, which was solved numerically, taking into account isotropic hyperfine coupling with five nuclear spins (1 N on donor radical, 4 H on acceptor radical) and anisotropic hyperfine coupling with the nitrogen nucleus at the donor radical. The results of the quantum calculations serve as a rigorous basis of interpreting the classical parameter k±. Furthermore, it is demonstrated that the incoherent part of spin motion is essential for a full understanding of the charge recombination kinetics even in the "coherent" regime.

Original languageEnglish
Pages (from-to)197-223
Number of pages27
JournalZeitschrift fur Physikalische Chemie
Volume231
Issue number2
DOIs
Publication statusPublished - 1 Feb 2017

Keywords

  • charge recombination
  • linked radical pairs
  • spin chemistry
  • spin relaxation

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