Abstract：
A long-standing question in electron transfer research concerns the number and identity of collective nuclear motions that drive electron transfer or localisation. It is well established that these nuclear motions are commonly gathered into a so-called electron transfer coordinate. In this theoretical study, we demonstrate that both anti-symmetric and symmetric vibrational motions are intrinsic to bridged systems, and that both are required to explain the characteristic shape of their intervalence charge transfer bands. Using the properties of a two-state Marcus-Hush model, we identify and quantify these two coordinates as linear combinations of normal modes from ab initio calculations. This quantification gives access to the potential coupling, reorganization energy and curvature of the potential energy surfaces involved in electron transfer, independent of any prior assumptions about the system of interest. We showcase these claims with the Creutz-Taube ion, a prototypical Class III mixed valence complex. We find that the symmetric dimension is responsible for the asymmetric band shape, and trace this back to the offset of the ground and excited state potentials in this dimension. The significance of the symmetric dimension originates from geometry dependent coupling, which in turn is a natural consequence of the well-established superexchange mechanism. The conceptual connection between the symmetric and anti-symmetric motions and the superexchange mechanism appears as a general result for bridged systems.
摘要：
电子转移研究中的一个长期存在的问题涉及驱动电子转移或局部化的集体核运动的数量和身份。众所周知，这些核运动通常会聚集到所谓的电子转移坐标中。在这项理论研究中，我们证明了非对称和对称振动运动都是桥接系统固有的，两者都需要解释它们的价间电荷转移带的特征形状。使用两状态Marcus-Hush模型的属性，我们从从头计算中将这两个坐标识别和量化为正常模式的线性组合。这种量化提供了对潜在耦合的访问，参与电子转移的势能面的重组能和曲率，独立于对感兴趣的系统的任何先前假设。我们用Creutz-Taube离子展示了这些主张，典型的III类混合价络合物。我们发现对称维度是不对称能带形状的原因，并将其追溯到该维度中接地和激发态电势的偏移。对称尺寸的重要性源于几何相关的耦合，这反过来又是完善的超交换机制的自然结果。对称和反对称运动与超交换机制之间的概念联系似乎是桥接系统的一般结果。
