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P J Hore - One of the best experts on this subject based on the ideXlab platform.
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asymmetric recombination and electron spin relaxation in the Semiclassical Theory of radical pair reactions
Journal of Chemical Physics, 2014Co-Authors: Alan M Lewis, David E Manolopoulos, P J HoreAbstract:We describe how the Semiclassical Theory of radical pair recombination reactions recently introduced by two of us [D. E. Manolopoulos and P. J. Hore, J. Chem. Phys. 139, 124106 (2013)] can be generalised to allow for different singlet and triplet recombination rates. This is a non-trivial generalisation because when the recombination rates are different the recombination process is dynamically coupled to the coherent electron spin dynamics of the radical pair. Furthermore, because the recombination operator is a two-electron operator, it is no longer sufficient simply to consider the two electrons as classical vectors: one has to consider the complete set of 16 two-electron spin operators as independent classical variables. The resulting Semiclassical Theory is first validated by comparison with exact quantum mechanical results for a model radical pair containing 12 nuclear spins. It is then used to shed light on the spin dynamics of a carotenoid-porphyrin-fullerene triad containing considerably more nucl...
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asymmetric recombination and electron spin relaxation in the Semiclassical Theory of radical pair reactions
arXiv: Chemical Physics, 2014Co-Authors: Alan M Lewis, David E Manolopoulos, P J HoreAbstract:We describe how the Semiclassical Theory of radical pair recombination reactions recently introduced by two of us [D. E. Manolopoulos and P. J. Hore, J. Chem. Phys. 139, 124106 (2013)] can be generalised to allow for different singlet and triplet recombination rates. This is a non-trivial generalisation because when the recombination rates are different the recombination process is dynamically coupled to the coherent electron spin dynamics of the radical pair. Furthermore, because the recombination operator is a two-electron operator, it is no longer sufficient simply to consider the two electrons as classical vectors: one has to consider the complete set of 16 two-electron spin operators as independent classical variables. The resulting Semiclassical Theory is first validated by comparison with exact quantum mechanical results for a model radical pair containing 12 nuclear spins. It is then used to shed light on the spin dynamics of a carotenoid-porphyrin-fullerene (CPF) triad containing considerably more nuclear spins which has recently been used to establish a 'proof of principle' for the operation of a chemical compass [K. Maeda et al., Nature 453, 387 (2008)]. We find in particular that the intriguing biphasic behaviour that has been observed in the effect of an Earth-strength magnetic field on the time-dependent survival probability of the photo-excited C+PF- radical pair arises from a delicate balance between its asymmetric recombination and the relaxation of the electron spin in the carotenoid radical.
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an improved Semiclassical Theory of radical pair recombination reactions
Journal of Chemical Physics, 2013Co-Authors: David E Manolopoulos, P J HoreAbstract:We present a practical Semiclassical method for computing the electron spin dynamics of a radical in which the electron spin is hyperfine coupled to a large number of nuclear spins. This can be used to calculate the singlet and triplet survival probabilities and quantum yields of radical recombination reactions in the presence of magnetic fields. Our method differs from the early Semiclassical Theory of Schulten and Wolynes [J. Chem. Phys. 68, 3292 (1978)] in allowing each individual nuclear spin to precess around the electron spin, rather than assuming that the hyperfine coupling-weighted sum of nuclear spin vectors is fixed in space. The downside of removing this assumption is that one can no longer obtain a simple closed-form expression for the electron spin correlation tensor: our method requires a numerical calculation. However, the computational effort increases only linearly with the number of nuclear spins, rather than exponentially as in an exact quantum mechanical calculation. The method is therefore applicable to arbitrarily large radicals. Moreover, it approaches quantitative agreement with quantum mechanics as the number of nuclear spins increases and the environment of the electron spin becomes more complex, owing to the rapid quantum decoherence in complex systems. Unlike the Schulten-Wolynes Theory, the present Semiclassical Theory predicts the correct long-time behaviour of the electron spin correlation tensor, and it therefore correctly captures the low magnetic field effect in the singlet yield of a radical recombination reaction with a slow recombination rate.
David E Manolopoulos - One of the best experts on this subject based on the ideXlab platform.
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asymmetric recombination and electron spin relaxation in the Semiclassical Theory of radical pair reactions
Journal of Chemical Physics, 2014Co-Authors: Alan M Lewis, David E Manolopoulos, P J HoreAbstract:We describe how the Semiclassical Theory of radical pair recombination reactions recently introduced by two of us [D. E. Manolopoulos and P. J. Hore, J. Chem. Phys. 139, 124106 (2013)] can be generalised to allow for different singlet and triplet recombination rates. This is a non-trivial generalisation because when the recombination rates are different the recombination process is dynamically coupled to the coherent electron spin dynamics of the radical pair. Furthermore, because the recombination operator is a two-electron operator, it is no longer sufficient simply to consider the two electrons as classical vectors: one has to consider the complete set of 16 two-electron spin operators as independent classical variables. The resulting Semiclassical Theory is first validated by comparison with exact quantum mechanical results for a model radical pair containing 12 nuclear spins. It is then used to shed light on the spin dynamics of a carotenoid-porphyrin-fullerene triad containing considerably more nucl...
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asymmetric recombination and electron spin relaxation in the Semiclassical Theory of radical pair reactions
arXiv: Chemical Physics, 2014Co-Authors: Alan M Lewis, David E Manolopoulos, P J HoreAbstract:We describe how the Semiclassical Theory of radical pair recombination reactions recently introduced by two of us [D. E. Manolopoulos and P. J. Hore, J. Chem. Phys. 139, 124106 (2013)] can be generalised to allow for different singlet and triplet recombination rates. This is a non-trivial generalisation because when the recombination rates are different the recombination process is dynamically coupled to the coherent electron spin dynamics of the radical pair. Furthermore, because the recombination operator is a two-electron operator, it is no longer sufficient simply to consider the two electrons as classical vectors: one has to consider the complete set of 16 two-electron spin operators as independent classical variables. The resulting Semiclassical Theory is first validated by comparison with exact quantum mechanical results for a model radical pair containing 12 nuclear spins. It is then used to shed light on the spin dynamics of a carotenoid-porphyrin-fullerene (CPF) triad containing considerably more nuclear spins which has recently been used to establish a 'proof of principle' for the operation of a chemical compass [K. Maeda et al., Nature 453, 387 (2008)]. We find in particular that the intriguing biphasic behaviour that has been observed in the effect of an Earth-strength magnetic field on the time-dependent survival probability of the photo-excited C+PF- radical pair arises from a delicate balance between its asymmetric recombination and the relaxation of the electron spin in the carotenoid radical.
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an improved Semiclassical Theory of radical pair recombination reactions
Journal of Chemical Physics, 2013Co-Authors: David E Manolopoulos, P J HoreAbstract:We present a practical Semiclassical method for computing the electron spin dynamics of a radical in which the electron spin is hyperfine coupled to a large number of nuclear spins. This can be used to calculate the singlet and triplet survival probabilities and quantum yields of radical recombination reactions in the presence of magnetic fields. Our method differs from the early Semiclassical Theory of Schulten and Wolynes [J. Chem. Phys. 68, 3292 (1978)] in allowing each individual nuclear spin to precess around the electron spin, rather than assuming that the hyperfine coupling-weighted sum of nuclear spin vectors is fixed in space. The downside of removing this assumption is that one can no longer obtain a simple closed-form expression for the electron spin correlation tensor: our method requires a numerical calculation. However, the computational effort increases only linearly with the number of nuclear spins, rather than exponentially as in an exact quantum mechanical calculation. The method is therefore applicable to arbitrarily large radicals. Moreover, it approaches quantitative agreement with quantum mechanics as the number of nuclear spins increases and the environment of the electron spin becomes more complex, owing to the rapid quantum decoherence in complex systems. Unlike the Schulten-Wolynes Theory, the present Semiclassical Theory predicts the correct long-time behaviour of the electron spin correlation tensor, and it therefore correctly captures the low magnetic field effect in the singlet yield of a radical recombination reaction with a slow recombination rate.
Wolfgang L Wiese - One of the best experts on this subject based on the ideXlab platform.
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experimental stark widths and shifts for spectral lines of neutral and ionized atoms a critical review of selected data for the period 1989 through 2000
Journal of Physical and Chemical Reference Data, 2002Co-Authors: N Konjevic, A Lesage, Jeffrey R Fuhr, Wolfgang L WieseAbstract:A critical review of the available experimental data on Stark widths and shifts for spectral lines of nonhydrogenic neutral atoms and positive ions has been carried out. The review covers the period from 1989 through the end of 2000 and represents a continuation of earlier critical reviews up to 1988. Data tables containing the selected experimental Stark broadening parameters are presented with estimated accuracies. Guidelines for the accuracy estimates, developed during the previous reviews, are summarized again. The data are arranged according to elements and spectra, and these are presented in alphabetical and numerical order, respectively. A total of 77 spectra are covered, and the material on multiply charged ions has significantly increased. Comparisons with comprehensive calculations based on Semiclassical Theory are made whenever possible, since the comparison with Theory has often been a principal motivation for the experiments.
Alan M Lewis - One of the best experts on this subject based on the ideXlab platform.
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asymmetric recombination and electron spin relaxation in the Semiclassical Theory of radical pair reactions
Journal of Chemical Physics, 2014Co-Authors: Alan M Lewis, David E Manolopoulos, P J HoreAbstract:We describe how the Semiclassical Theory of radical pair recombination reactions recently introduced by two of us [D. E. Manolopoulos and P. J. Hore, J. Chem. Phys. 139, 124106 (2013)] can be generalised to allow for different singlet and triplet recombination rates. This is a non-trivial generalisation because when the recombination rates are different the recombination process is dynamically coupled to the coherent electron spin dynamics of the radical pair. Furthermore, because the recombination operator is a two-electron operator, it is no longer sufficient simply to consider the two electrons as classical vectors: one has to consider the complete set of 16 two-electron spin operators as independent classical variables. The resulting Semiclassical Theory is first validated by comparison with exact quantum mechanical results for a model radical pair containing 12 nuclear spins. It is then used to shed light on the spin dynamics of a carotenoid-porphyrin-fullerene triad containing considerably more nucl...
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asymmetric recombination and electron spin relaxation in the Semiclassical Theory of radical pair reactions
arXiv: Chemical Physics, 2014Co-Authors: Alan M Lewis, David E Manolopoulos, P J HoreAbstract:We describe how the Semiclassical Theory of radical pair recombination reactions recently introduced by two of us [D. E. Manolopoulos and P. J. Hore, J. Chem. Phys. 139, 124106 (2013)] can be generalised to allow for different singlet and triplet recombination rates. This is a non-trivial generalisation because when the recombination rates are different the recombination process is dynamically coupled to the coherent electron spin dynamics of the radical pair. Furthermore, because the recombination operator is a two-electron operator, it is no longer sufficient simply to consider the two electrons as classical vectors: one has to consider the complete set of 16 two-electron spin operators as independent classical variables. The resulting Semiclassical Theory is first validated by comparison with exact quantum mechanical results for a model radical pair containing 12 nuclear spins. It is then used to shed light on the spin dynamics of a carotenoid-porphyrin-fullerene (CPF) triad containing considerably more nuclear spins which has recently been used to establish a 'proof of principle' for the operation of a chemical compass [K. Maeda et al., Nature 453, 387 (2008)]. We find in particular that the intriguing biphasic behaviour that has been observed in the effect of an Earth-strength magnetic field on the time-dependent survival probability of the photo-excited C+PF- radical pair arises from a delicate balance between its asymmetric recombination and the relaxation of the electron spin in the carotenoid radical.
A V Turbiner - One of the best experts on this subject based on the ideXlab platform.
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fluctuations in quantum mechanics and field theories from a new version of Semiclassical Theory ii
Physical Review D, 2017Co-Authors: M A Escobarruiz, Edward Shuryak, A V TurbinerAbstract:This is the second paper on the Semiclassical approach based on the density matrix given by the Euclidean time path integral with fixed coinciding end points. The classical path, interpolating between this point and the classical vacuum (called a “flucton”), as well as systematic one- and two-loop corrections were calculated in the first paper [M. A. Escobar-Ruiz, E. Shuryak, and A. V. Turbiner, Phys. Rev. D 93, 105039 (2016)]PRVDAQ2470-001010.1103/PhysRevD.93.105039 for a double-well potential. Here, we extend them for a number of quantum-mechanical problems, such as an anharmonic oscillator and the sine-Gordon potential. The method is based on a systematic expansion in Feynman diagrams and thus can be extended to quantum field theories (QFTs). We show that the loop expansion in quantum mechanics resembles the leading-log approximations in QFT. In this sequel, we present a complete set of results obtained using this method in a unified way. Alternatively, starting from the Schrodinger equation we derive a generalized Bloch equation whose Semiclassical-like, iterative solution generates the loop expansion. We rederive the two-loop expansions for all three of the above potentials and extend them to three loops, which has not yet been done via Feynman diagrams. All results for both methods are fully consistent with each other. An asymmetric (tilted) double-well potential (nondegenerate minima) is also studied using the second method.
