Department of Chemistry, University of Wisconsin , Madison, Wisconsin 53706, United States.
J Phys Chem A. 2013 Nov 27;117(47):12401-8. doi: 10.1021/jp409377a. Epub 2013 Nov 7.
This article describes the new multidimensional spectroscopy technique triply resonant sum frequency spectroscopy, a four-wave mixing technique sharing advantages of both 2D-IR and resonance Raman experiments. In this technique, lasers with three independent frequencies interact coherently within a sample and generate an output frequency at their triple summation. The output intensity depends on coupled electronic and vibrational resonances in the sample. We use an organic dye as a model system to demonstrate fully resonant, fully coherent multidimensional spectroscopy using two independently tunable mid-infrared vibrational interactions and one visible electronic interaction. When the pulses are time ordered, the method has a single coherence pathway, eliminating interference between pathways. Fundamental vibrational transitions appear on one axis and overtones and combinations bands on the other, allowing anharmonicities of the modes to be determined easily and conveying molecular coupling information. The experiments demonstrate coupling between seven vibrational ring modes and an electronic state, the resolution of a Fermi resonance, detection of low concentrations, elimination of excitation pulse scattering and fluorescence, background suppression of solvent and co-solutes, and observation of coherence dephasing dynamics. The electronic resonance enhancements used in this methodology are similar to the enhancements responsible for resonance Raman spectroscopy and can be considered resonance 2D-IR spectroscopy.
本文描述了一种新的多维光谱技术——三重共振和频光谱，它是一种四波混频技术，结合了 2D-IR 和共振拉曼实验的优点。在该技术中，三个独立频率的激光在样品内相干地相互作用，产生它们三重和的输出频率。输出强度取决于样品中耦合的电子和振动共振。我们使用有机染料作为模型系统，演示了使用两个独立可调谐的中红外振动相互作用和一个可见电子相互作用的完全共振、完全相干多维光谱。当脉冲有序时，该方法具有单个相干途径，消除了途径之间的干扰。基本振动跃迁出现在一个轴上，泛频和组合带出现在另一个轴上，从而可以轻松确定模式的非谐性，并传递分子耦合信息。实验证明了七个振动环模式与一个电子态之间的耦合，费米共振的分辨率，低浓度的检测，消除激发脉冲散射和荧光，溶剂和共溶剂的背景抑制，以及相干退相动力学的观察。在这种方法中使用的电子共振增强与导致共振拉曼光谱的增强相似，可以被认为是共振 2D-IR 光谱。
