Modeling magnetic field effects in multispin systems

Magin, Ilya M.; Purtov, P. A.; Kruppa, Alexander I.; Leshina, T. V.

doi:10.1007/bf03166569

Cited by 11 publications

(17 citation statements)

References 14 publications

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“…Another close example is a three-spin system biradical-ion/radical ion with exchange interaction within the biradical and hyperfine interaction with a nucleus in either partner (Lukzen et al, 2002;Verkhovlyuk et al 2007), where a nucleus in the biradical ion produces an anticrossing near the main line of J-resonance in the biradical, while a nucleus in the 295 radical partner produces a crossing. Similar dichotomy is also observed in magnetic effects in a biradical/stable radical complex with different distributions of inter-and intra-partner exchange interactions (Magin et al 2004;2009). https://doi.org/10.5194/mr-2021-6…”

Section: S N N …supporting

confidence: 65%

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2021

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In this work we derive conditions under which a level crossing line in magnetic field effect curve for a recombining radical pair will be equivalent to ESR spectrum, and discuss three simple rules for qualitative prediction of the level crossing spectra. Introduction 10Spin-correlated nature of radical (ion) pairs arising as intermediates in many natural or induced chemical transformations gives rise to a host of "magnetic and spin effects" in chemical reactions. It all started with observing (Bargon, 1967;Ward and Lawler, 1967) and understanding (Closs, 1969;Kaptein and Oosterhoff, 1969) strange-looking "polarized" NMR spectra, and has evolved into a mature field in itself with a wide range of powerful experimental and theoretical techniques relying on magnetically manipulating spins in chemical processes (Salikhov et al., 1984; Steiner and Ulrich, 1989; Hayashi, 15 2004), culminating in the modern high-tech finesse of advanced hyperpolarized NMR (Ivanov et al., 2014). This paper deals with a curious bridge between the most humble magnetic field effect curves (MFE), i.e., dependence of reaction yield on applied static magnetic field, and hyperpolarized NMR: additional sharp resonance-like lines that may occur against the smooth background of MFE due to genuine level crossings in the spin system of the radical pair. The lines were first discovered in zero magnetic field (Anisimov et al. 1983;Fischer, 1983) and attributed to 20 interference of pair states in the higher, spherical, symmetry conditions of zero external field similar to Hanle effect in atomic spectroscopy (Hanle, 1924). The zero field line, or Low Field Effect, was then put to the front as the possible physical mechanism of magnetoreception, and the research that followed was plenty. However, this completely overshadowed the other, spectroscopic, aspect of the level crossing lines possible in field other than zero.

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Section: S N N …supporting

confidence: 65%

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2021

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“…Another close example is a three-spin system biradical ion/radical ion with an ex-change interaction within the biradical and hyperfine interaction with a nucleus in either partner (Lukzen et al, 2002;Verkhovlyuk et al, 2007), where a nucleus in the biradical ion produces an anticrossing near the main line of J resonance in the biradical, while a nucleus in the radical partner produces a crossing. A similar dichotomy is also observed in magnetic effects in a biradical/stable radical complex with different distributions of inter-and intra-partner exchange interactions (Magin et al, 2004(Magin et al, , 2005(Magin et al, , 2009.…”

Section: Introducing Nuclei Into the Driving Partner: Crossings Vs Ansupporting

confidence: 67%

Simple rules for resolved level-crossing spectra in magnetic field effects on reaction yields

2021

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“…As the Zeeman part of the Hamiltonian commutes with the exchange Hamiltonian, this interaction alone is insufficient to produce MFEs (see SI [32]). However, mutual exchange coupling can provide the premise for near level-crossings at certain strengths of an external magnetic field, whereupon hyperfine-driven spin conversion can proceed efficiently [33,34], and may also transmit the effect of a fast-relaxing third radical [35]. A perturbative approach based on a Hubbard-trimer Hamiltonian has been used to show that the additional radical can enhance the intersystem crossing rate [36].…”

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Magnetosensitivity in Dipolarly Coupled Three-Spin Systems

2018

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The Radical Pair Mechanism is a canonical model for the magnetosensitivity of chemical reaction processes. The key ingredient of this model is the hyperfine interaction that induces a coherent mixing of singlet and triplet electron spin states in pairs of radicals, thereby facilitating magnetic field effects (MFEs) on reaction yields through spin-selective reaction channels. We show that the hyperfine interaction is not a categorical requirement to realize the sensitivity of radical reactions to weak magnetic fields. We propose that, in systems comprising three instead of two radicals, dipolar interactions provide an alternative pathway for MFEs. By considering the role of symmetries and energy level crossings, we present a model that demonstrates a directional sensitivity to fields weaker than the geomagnetic field and remarkable spikes in the reaction yield as a function of the magnetic field intensity; these effects can moreover be tuned by the exchange interaction. Our results further the current understanding of the effects of weak magnetic fields on chemical reactions, could pave the way to a clearer understanding of the mysteries of magnetoreception and other biological MFEs and motivate the design of quantum sensors. Further still, this phenomenon will affect spin systems used in quantum information processing in the solid state and may also be applicable to spintronics.There is growing excitement about the possibility of quantum coherence and entanglement underpinning the optimal functioning of biological processes [1]. A notable example is the avian inclination compass [2][3][4][5][6][7][8][9][10][11][12], which has recently been realised as a truly quantum-biological process [3]. The leading explanation of this phenomenon utilizes the Radical Pair Mechanism (RPM), which describes the unitary evolution of singlet-triplet (S-T) coherences in systems comprising two radicals, i.e. two electron spins [2,13,14]. The RPM has also been suggested to underpin controversial health-related implications of exposure to weak electromagnetic fields [15][16][17][18]. For these phenomena, the so-called low-field effect (LFE) is crucial to foster sensitivity to magnetic fields of intensity comparable to the geomagnetic field (≈ 50 µT) [6,[19][20][21][22][23][24]. The electron-electron dipolar interaction is often neglected when addressing MFEs within the RPM framework, but preliminary explorations have been conducted: electron-electron dipolar coupling is expected to resemble the exchange coupling, which, as the dominant interaction, suppresses S-T conversion by lifting the neardegeneracy of triplet and singlet states, reducing their susceptibility to mixing by weak hyperfine interactions [25], and quenching the LFE [26]. Efimova et al. proposed that the dipolar interaction could be partly compensated by the exchange interaction, thereby allowing high sensitivity to the geomagnetic field despite sizeable electron-electron dipolar coupling interactions [27].In contrast to the two-spin systems of the classical RPM, spin tr...

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Modeling magnetic field effects in multispin systems

Cited by 11 publications

References 14 publications

Comment on mr-2021-6

Comment on mr-2021-6

Simple rules for resolved level-crossing spectra in magnetic field effects on reaction yields

Magnetosensitivity in Dipolarly Coupled Three-Spin Systems

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