Photosystem II (PSII) is the only biological system capable of splitting water to molecular oxygen. Its reaction center (RC) is responsible for the primary charge separation that drives the water oxidation reaction. In this work, we revisit the spectroscopic properties of the PSII RC using the complex time-dependent Redfield (ctR) theory for optical lineshapes [A. Gelzinis et al., J. Chem. Phys. 142, 154107 (2015)]. We obtain the PSII RC model parameters (site energies, disorder, and reorganization energies) from the fits of several spectra and then further validate the model by calculating additional independent spectra. We obtain good to excellent agreement between theory and calculations. We find that overall our model is similar to some of the previous asymmetric exciton models of the PSII RC. On the other hand, our model displays differences from previous work based on the modified Redfield theory. We extend the ctR theory to describe the Stark spectrum and use its fit to obtain the parameters of a single charge transfer state included in our model. Our results suggest that $Ch{l}_{D1}^{+}Phe{o}_{D1}^{-}$ is most likely the primary charge transfer state, but that the Stark spectrum of the PSII RC is probably also influenced by other states.

中文翻译：

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再谈光系统II反应中心的光谱性质

光系统II（PSII）是唯一能够将水分解为分子氧的生物系统。它的反应中心（RC）负责驱动水氧化反应的主电荷分离。在这项工作中，我们使用复杂的与时间有关的Redfield（ctR）理论对光学线形重新审视PSII RC的光谱特性[A. Gelzinis等。，J. Chem。物理 142，154107（2015）]。我们从几个光谱的拟合中获得PSII RC模型参数（位能，无序度和重组能），然后通过计算其他独立光谱进一步验证模型。我们在理论和计算之间取得了很好的一致性。我们发现总体而言，我们的模型与PSII RC的某些先前非对称激子模型相似。另一方面，我们的模型显示了与基于改进的Redfield理论的先前工作的不同之处。我们扩展了ctR理论来描述Stark光谱，并利用其拟合获得模型中包含的单个电荷转移状态的参数。我们的结果表明$CH{升}_{d\mathrm{1个}}^{+}PHË{Ø}_{d\mathrm{1个}}^{-}$ 可能是主电荷转移状态，但PSII RC的Stark光谱也可能受到其他状态的影响。