Influence of geminate recombination kinetics on the shape of low field MARY line

Toropov, Yu. V.; Sviridenko, F. B.; Stass, Dmitri V.; Doktorov, A.B.; Molin, Yu. N.

doi:10.1016/s0301-0104(99)00403-6

Cited by 21 publications

(8 citation statements)

References 15 publications

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“…Previous MARY studies have revealed that not only the width of LC-derived features is sensitive to k sc but that their shape also reflects the distribution of RP lifetimes. 63 In supplementary material, we demonstrate that similar effects are expected for ls-CIDNP: comparison of the diffusional model and the exponential model show quite a different behavior (the calculation of CIDNP is done using the same method as described in Refs. 64 and 65).…”

Section: Isotropic Case J Ex =supporting

confidence: 53%

Level crossing analysis of chemically induced dynamic nuclear polarization: Towards a common description of liquid-state and solid-state cases

Sosnovsky

Jeschke

Matysik

et al. 2016

The Journal of Chemical Physics

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Chemically Induced Dynamic Nuclear Polarization (CIDNP) is an efficient method of creating non-equilibrium polarization of nuclear spins by using chemical reactions, which have radical pairs as intermediates. The CIDNP effect originates from (i) electron spin-selective recombination of radical pairs and (ii) the dependence of the inter-system crossing rate in radical pairs on the state of magnetic nuclei. The CIDNP effect can be investigated by using Nuclear Magnetic Resonance (NMR) methods. The gain from CIDNP is then two-fold: it allows one to obtain considerable amplification of NMR signals; in addition, it provides a very useful tool for investigating elusive radicals and radical pairs. While the mechanisms of the CIDNP effect in liquids are well established and understood, detailed analysis of solid-state CIDNP mechanisms still remains challenging; likewise a common theoretical frame for the description of CIDNP in both solids and liquids is missing. Difficulties in understanding the spin dynamics that lead to the CIDNP effect in the solid-state case are caused by the anisotropy of spin interactions, which increase the complexity of spin evolution. In this work, we propose to analyze CIDNP in terms of level crossing phenomena, namely, to attribute features in the CIDNP magnetic field dependence to Level Crossings (LCs) and Level Anti-Crossings (LACs) in a radical pair. This approach allows one to describe liquid-state CIDNP; the same holds for the solid-state case where anisotropic interactions play a significant role in CIDNP formation. In solids, features arise predominantly from LACs, since in most cases anisotropic couplings result in perturbations, which turn LCs into LACs. We have interpreted the CIDNP mechanisms in terms of the LC/LAC concept. This consideration allows one to find analytical expressions for a wide magnetic field range, where several different mechanisms are operative; furthermore, the LAC description gives a way to determine CIDNP sign rules. Thus, LCs/LACs provide a consistent description of CIDNP in both liquids and solids with the prospect of exploiting it for the analysis of short-lived radicals and for optimizing the polarization level.

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Section: Isotropic Case J Ex =supporting

confidence: 53%

Level crossing analysis of chemically induced dynamic nuclear polarization: Towards a common description of liquid-state and solid-state cases

Sosnovsky

Jeschke

Matysik

et al. 2016

The Journal of Chemical Physics

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“…6 Indeed, as reported, 6 the spin-lattice relaxation time of trans-decalin radical cation is 7 ns. The re-evaluated data of that work according to a more accurate theory 24 will provide a value of about 14 ns, which coincides with the T 1 value given in Table 1.…”

Section: Discussionsupporting

confidence: 77%

Paramagnetic relaxation of cyclohexane radical cation in solution as measured by the method of time-resolved magnetic field effect

Borovkov

Molin

2004

Phys. Chem. Chem. Phys.

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“…For the second moment of the ESR spectrum of the p-TP radical anion and the lifetime of the 1 p-TP* singlet excited state, we used the known values σ a ) 0.068 mT 15 and τ fl ) 1 ns. 25 For the recombination kinetics of ion pairs in eq 2 we took the function 26 The best agreement between the experimental and model kinetics was observed for t 0 values varying over the range 3-5 ns depending on the added alkane and its concentration. In any case, a 2-3-fold change in t 0 had a negligible effect on the calculated TR MFE curves except for an initial portion of the curves within several nanoseconds where the geminate recombination rate of the radical ion pairs decreases sharply by 1-2 orders of magnitude.…”

Section: Resultsmentioning

confidence: 99%

“…In any case, a 2−3-fold change in t 0 had a negligible effect on the calculated TR MFE curves except for an initial portion of the curves within several nanoseconds where the geminate recombination rate of the radical ion pairs decreases sharply by 1−2 orders of magnitude. The use of other functions often applied for approximating geminate recombination kinetics instead of (10) (see, e.g., ref ) had no noticeable effect on the results obtained from the fitting. The reason for this is a rather short fluorescence lifetime of 1 p- TP* (of about 1 ns).…”

Section: Resultsmentioning

confidence: 99%

Degenerate Electron Exchange Reaction of n-Alkane Radical Cations in Solution

et al. 2006

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The degenerate electron exchange (DEE) reaction involving radical cations (RCs) of n-nonane, n-dodecane, and n-hexadecane in n-hexane solution was studied over the temperature range 253-313 K using the method of time-resolved magnetic field effect in recombination fluorescence of spin-correlated radical ion pairs. In the dilute solutions the rate constant of DEE was found to be 200 times slower than the diffusion limit. Using n-nonane as an example, we showed that two reasons are responsible for the low value of the RC self-exchange rate: (1) conformational variability of molecules and RCs and (2) the activation barrier of DEE reaction. The calculations of the reaction enthalpy performed by the B3LYP/6-31G(d) method indicated that electron transfer can be effective only upon collision of RC with a neutral molecule either in the all-trans conformation or in the conformation differing from the latter by rotation of the end ethyl fragment. The activation barrier of the DEE reaction was estimated using the reorganization energy of the internal degrees of freedom calculated at the B3LYP level and was found to be about 6 kcal/mol. A possible influence of the interaction between RC and a neutral molecule in an encounter complex on DEE rate constant is also discussed.

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Influence of geminate recombination kinetics on the shape of low field MARY line

Cited by 21 publications

References 15 publications

Level crossing analysis of chemically induced dynamic nuclear polarization: Towards a common description of liquid-state and solid-state cases

Level crossing analysis of chemically induced dynamic nuclear polarization: Towards a common description of liquid-state and solid-state cases

Paramagnetic relaxation of cyclohexane radical cation in solution as measured by the method of time-resolved magnetic field effect

Degenerate Electron Exchange Reaction of n-Alkane Radical Cations in Solution

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