Two-dimensional resonance Raman (2DRR) spectroscopy has been developed for studies of photochemical reaction mechanisms and structural heterogeneity in condensed phase systems. 2DRR spectroscopy is motivated by knowledge of non-equilibrium effects that cannot be detected with traditional resonance Raman spectroscopy. For example, 2DRR spectra may reveal correlated distributions of reactant and product geometries in systems that undergo chemical reactions on the femtosecond time scale. Structural heterogeneity in an ensemble may also be reflected in the 2D spectroscopic line shapes of both reactive and non-reactive systems. In this chapter, these capabilities of 2DRR spectroscopy are discussed in the context of recent applications to the photodissociation reactions of triiodide. We show that signatures of “vibronic coherence transfer” in the photodissociation process can be targeted with particular 2DRR pulse sequences. Key differences between the signal generation mechanisms for 2DRR and off-resonant 2D Raman spectroscopy techniques are also addressed. Overall, recent experimental developments and applications of the 2DRR method suggest that it will be a valuable tool for elucidating ultrafast chemical reaction mechanisms.

二维共振拉曼（2DRR）光谱学已被开发用于研究凝聚相系统中的光化学反应机理和结构异质性。2DRR光谱法是由非平衡效应的知识激发的，而传统的共振拉曼光谱法则无法检测到非平衡效应。例如，2DRR光谱可以揭示在飞秒时间尺度上发生化学反应的系统中反应物和产物几何形状的相关分布。整体中的结构异质性也可以反映在反应性和非反应性系统的2D光谱线形中。在本章中，将在三碘化物的光解离反应的最新应用中讨论2DRR光谱学的这些功能。我们表明光解离过程中的“振动相干转移”的签名可以针对特定的2DRR脉冲序列。还解决了2DRR和非共振2D拉曼光谱技术的信号生成机制之间的关键区别。总体而言，最近的实验发展和2DRR方法的应用表明，它将是阐明超快化学反应机理的有价值的工具。