自由基对系间交叉：量子动力学还是非相干动力学？
Radical pair intersystem crossing: Quantum dynamics or incoherent kinetics?
摘要：
磁场对自由基对反应的影响是由于相干电子自旋动力学和自旋弛豫效应的相互作用而产生的，对其的严格处理需要Liouville-von Neumann方程的解。然而，人们经常发现，简单的非相干动力学模型的自由基对单重态-三重态系间交叉提供了一个可接受的描述实验测量。在本文中，我们概述了这种非相干动力学描述的理论基础，阐明了它与精确量子力学的联系。我们特别展示了自由基对自旋态的有限寿命，以及任何额外的自旋态退相，导致非相干的系间交叉。我们得到了自由基对自旋态相互转换率的简单表达式，Steiner等人最近提出的函数形式[J. Phys. Chem. C 122，11701（2018）]可以被视为近似值。我们还测试了动力学主方程对精确的量子动力学模拟的模型自由基对和一系列的$\text{PTZ}^{\bullet+}\text{-Ph}_\text{n}\text{-PDI}^{\bullet-}$分子线。
英文摘要：
Magnetic field effects on radical pair reactions arise due to the interplay of coherent electron spin dynamics and spin relaxation effects, a rigorous treatment of which requires the solution of the Liouville-von Neumann equation. However, it is often found that simple incoherent kinetic models of the radical pair singlet-triplet intersystem crossing provide an acceptable description of experimental measurements. In this paper we outline the theoretical basis for this incoherent kinetic description, elucidating its connection to exact quantum mechanics. We show in particular how the finite lifetime of the radical pair spin states, as well as any additional spin-state dephasing, leads to incoherent intersystem crossing. We arrive at simple expressions for the radical pair spin state interconversion rates to which the functional form proposed recently by Steiner et al. [J. Phys. Chem. C 122, 11701 (2018)] can be regarded as an approximation. We also test the kinetic master equation against exact quantum dynamical simulations for a model radical pair and for a series of $\text{PTZ}^{\bullet+}\text{-Ph}_\text{n}\text{-PDI}^{\bullet-}$ molecular wires.
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