Gandman Andrey, Mackin Robert, Cohn Bar, Rubtsov Igor V, Chuntonov Lev
Solid State Institute, Technion - Israel Institute of Technology , Haifa 32000, Israel.
Department of Chemistry, Tulane University , New Orleans, Louisiana 70118, United States.
J Phys Chem Lett. 2017 Jul 20;8(14):3341-3346. doi: 10.1021/acs.jpclett.7b01490. Epub 2017 Jul 10.
Two-dimensional femtosecond infrared (2DIR) spectroscopy routinely provides insights into molecular structure and ultrafast dynamics in 1-100 μm thick bulk samples. Confinement of molecules to surfaces, gaps, crevices, and other topographic features, frequently encountered on the nanometer length scale, significantly alters their structure and dynamics, affecting physical and chemical properties. Amplification of 2DIR signals by the plasmon-enhanced fields around metal nanostructures can permit structural and dynamics measurements of the confined molecules. Fano resonances, induced by the interaction between laser pulses, plasmon, and vibrational modes significantly distort 2D lineshapes. For different detuning from plasmon resonance, the interference between multiple signal components leads to different line shape asymmetry, which we demonstrate on a set of linear absorption, transient absorption, and 2DIR spectra. An intuitive model used to describe experimental data points to the interference's origin. Our results will facilitate the application of surface-enhanced 2DIR spectroscopy for studies of molecular structure and dynamics in a nanoconfined environment.
二维飞秒红外（2DIR）光谱通常能为1 - 100μm厚的块状样品的分子结构和超快动力学提供深入见解。分子被限制在纳米长度尺度上经常遇到的表面、间隙、裂缝和其他地形特征中时，会显著改变其结构和动力学，进而影响物理和化学性质。金属纳米结构周围的等离子体增强场对2DIR信号的放大作用，可以实现对受限分子的结构和动力学测量。激光脉冲、等离子体和振动模式之间的相互作用所诱导的法诺共振会显著扭曲二维线形。对于与等离子体共振的不同失谐，多个信号分量之间的干涉会导致不同的线形不对称性，我们在一组线性吸收、瞬态吸收和2DIR光谱上展示了这一点。一个用于描述实验数据的直观模型指出了干涉的起源。我们的结果将有助于表面增强2DIR光谱在纳米受限环境中分子结构和动力学研究中的应用。
