Coherence as an analytic tool of 2D electronic photon-echo spectroscopy: application to vibronic coupling

我们探索计算一个新的分析工具的二维（2D）光子回波（PE）光谱-所谓的拍地图-为了表征和分类振动耦合在这些实验观测。通过拍地图的分析是可能的，每当在2D PE实验中采用的激光脉冲导致激发和检测的相干振荡的分子系统中的研究。振荡携带关于激发态性质的信息，并且拍频图使得能够对该信息进行有效且可靠的分析。与传统的2D PE信号相比，拍频图的主要优点是其选择性（每个图选择一个特定的振荡）和灵敏度，甚至对非常弱的光学跃迁。因此，传统2D PE信号中存在的加宽和峰重叠显著减少，并且可以获得更精确和详细的信息。在这个项目中，我们使用拍频映射来探测电子振动耦合的起源。振子耦合，即电子自由度和原子核自由度之间的耦合，可能具有非常不同的物理性质和表现。最著名的例子是势能面的交叉和玻恩-奥本海默近似的崩溃。电子和核运动的不可分离性可能导致电子和核构型在同一时间尺度上的变化，并且通常负责反应动力学和电子转移和光保护等基本过程。有许多成熟的模型描述状态交叉。在这里，我们将解决避免交叉的模型，以及振动哈密顿模型通常用来描述动态圆锥路口。此外，我们还将考虑低聚物中电子振动耦合的最简单模型：电子振动二聚体。低聚物中的振动子效应在激子输运效率中起重要作用。在这些系统中，振动运动可以耦合到离域电子excitation.The项目的主要思想是表示所考虑的模型系统的性质在属于光学耦合电子态的系统本征态之间的偶极跃迁强度。这些偶极子直接有助于拍频图的形成。因此，我们希望观察到特定的模式，典型的每一个模型的振动耦合considered.The项目提供了一个基础，分类的振动相互作用的节拍地图。所有考虑的模型可以进一步扩展和参数化的具体应用。目前，只有极少数的实验组已经意识到了搏动图分析的潜力。我们设想，这项研究将鼓励进一步的实验实现。

We explore computationally a new analytic tool of two-dimensional (2D) photon-echo (PE) spectroscopy - so called beating maps - in order to characterize and classify vibronic coupling in terms of these experimental observables. The analysis by means of beating maps is possible whenever the laser pulses employed in a 2D PE experiment lead to excitation and detection of coherent oscillations in a molecular system under study. The oscillations carry information on the nature of the excited states, and the beating maps enable an efficient and reliable analysis of this information. The main advantage of the beating maps as compared to the conventional 2D PE signal is their selectivity (each map selects one particular oscillation) and sensitivity even to very weak optical transitions.As the result, broadening and peak overlaps present in conventional 2D PE signals are significantly reduced, and more precise and detailed information can be obtained.In this project, we employ the beating maps to probe the origin of vibronic coupling. Vibronic coupling, i.e. the coupling between electronic and nuclear degrees of freedom, may have quite distinct physical nature and manifestations. The most well known case is related to crossings of potential-energy surfaces and breakdown of Born-Oppenheimer approximation. The non-separability of electron and nuclear motion may lead to changes in electron and nuclear configurations at the same timescale and is often responsible for reaction dynamics and such fundamental processes as electron transfer and photoprotection. There is a number of well established models describing the state crossings. Here we will address the model of avoided crossing as well as the vibronic-Hamiltonian model commonly employed to describe dynamics at conical intersections. Further, we will also consider the simplest model of vibronic coupling in oligomers: a vibronic dimer. Vibronic effects in oligomers play an important role in the exciton transport efficiency. In these systems, vibrational motion may be coupled to delocalized electronic excitations.The main idea of the project is to express the properties of the considered model systems in terms of dipole transition strengths between the system eigenstates pertaining to optically coupled electronic states. These dipoles contribute directly to the formation of the beating maps. Therefore, we expect to observe specific patterns typical for each model of the vibronic coupling considered.The project provides a basis for classification of vibronic interactions by means of the beating maps. All the models considered can be further extended and parametrized for specific applications. Currently, only very few experimental groups have realized the potential of the beating-maps analysis.We envision that the research will encourage further experimental realizations.