Physikalisch-Chemisches Institut, Universität Heidelberg, Im Neuenheimer Feld 229, D-69120 Heidelberg, Germany.
J Chem Phys. 2012 Nov 14;137(18):184312. doi: 10.1063/1.4763979.
The quenching of the excitonic splitting in hydrogen-bonded molecular dimers has been explained recently in terms of exciton coupling theory, involving Förster's degenerate perturbation theoretical approach [P. Ottiger, S. Leutwyler, and H. Köppel, J. Chem. Phys. 136, 174308 (2012)]. Here we provide an alternative explanation based on the properties of the adiabatic potential energy surfaces. In the proper limit, the lower of these surfaces exhibits a double-minimum shape, with an asymmetric distortion that destroys the geometric equivalence of the excitonically coupled monomers. An effective mode is introduced that exactly reproduces the energy gain and amount of distortion that occurs in a multi-dimensional normal coordinate space. This allows to describe the quenched exciton splitting as the energy difference of the two (S(1) and S(2)) vibronic band origins in a one-dimensional (rather than multi-dimensional) vibronic calculation. The agreement with the earlier result (based on Förster theory) is excellent for all five relevant cases studied. A simple rationale for the quenched exciton splitting as nonadiabatic tunneling splitting on the lower double-minimum potential energy surface is given.
最近，人们根据涉及 Förster 简并微扰理论方法的激子耦合理论来解释氢键分子二聚体中激子分裂的猝灭[P. Ottiger, S. Leutwyler, and H. Köppel, J. Chem. Phys. 136, 174308 (2012)]。在这里，我们基于绝热势能面的性质提供了另一种解释。在适当的极限下，这些表面中的较低表面呈现出双势阱形状，具有不对称的变形，破坏了激子耦合单体的几何等效性。引入了一个有效的模式，它可以精确地再现多维正则坐标空间中发生的能量增益和变形量。这允许将猝灭的激子分裂描述为一维（而不是多维）振子计算中两个（S(1) 和 S(2)）振子带起源的能量差。对于研究的所有五个相关情况，与早期基于 Förster 理论的结果非常吻合。给出了将猝灭的激子分裂解释为下双势阱势能面上的非绝热隧道分裂的简单原理。
