International Tomography Center, Siberian Branch of the Russian Academy of Science, Novosibirsk 630090, Russia.
Department of Chemistry and Applied Biosciences, ETH Zürich, 8093 Zürich, Switzerland.
J Chem Phys. 2019 Mar 7;150(9):094105. doi: 10.1063/1.5077078.
The magnetic field dependence of Chemically Induced Dynamic Nuclear Polarization (CIDNP) in solid-state systems is analyzed theoretically with the aim to explain the puzzling sign change of polarization found at low fields [D. Gräsing et al., Sci. Rep. 7, 12111 (2017)]. We exploit the analysis of polarization in terms of level crossings and level anti-crossings trying to identify the positions of features in the CIDNP field dependence with specific crossings between spin energy levels of the radical pair. Theoretical treatment of solid-state CIDNP reveals a strong orientation dependence of polarization due to the spin dynamics conditioned by anisotropic spin interactions. Specifically, different anisotropic CIDNP mechanisms become active at different magnetic fields and different molecular orientations. Consequently, the field dependence and orientation dependence of polarization need to be analyzed together in order to rationalize experimental observations. By considering both magnetic field and orientation dependence of CIDNP, we are able to explain the previously measured CIDNP field dependence in photosynthetic reaction centers and to obtain a good qualitative agreement between the experimental observations and theoretical results.
本文从理论上分析了固态体系中化学诱导动态核极化（CIDNP）的磁场依赖性，旨在解释在低场下发现的极化符号令人困惑的变化[D. Gräsing 等人，Sci. Rep. 7, 12111 (2017)]。我们利用对交叉和反交叉的极化分析，试图确定 CIDNP 场依赖性中的特征位置与自由基对的自旋能级之间的特定交叉。固态 CIDNP 的理论处理揭示了由于各向异性自旋相互作用所决定的自旋动力学，极化具有很强的各向异性依赖性。具体来说，不同的各向异性 CIDNP 机制在不同的磁场和不同的分子取向下变得活跃。因此，为了合理化实验观察结果，需要同时分析极化的场依赖性和各向异性依赖性。通过考虑 CIDNP 的磁场和取向依赖性，我们能够解释先前在光合作用反应中心中测量的 CIDNP 场依赖性，并在实验观察结果和理论结果之间获得良好的定性一致性。
