Department of Chemistry, Louisiana State University, Baton Rouge, Louisiana 70803, USA.
J Chem Phys. 2023 Jul 21;159(3). doi: 10.1063/5.0154601.
Ultrafast two-dimensional infrared (2DIR) spectroscopy is a relatively new methodology, which has now been widely used to study the molecular structure and dynamics of molecular processes occurring in solution. Typically, in 2DIR spectroscopy the dynamics of a system is inferred from the evolution of 2DIR spectral features over waiting times. One of the most important metrics derived from the 2DIR is the frequency-frequency correlation function (FFCF), which can be extracted using different methods, including center and nodal line slope. However, these methods struggle to correctly describe the dynamics in 2DIR spectra with multiple and overlapping transitions. Here, a new approach, utilizing pseudo-Zernike moments, is introduced to retrieve the FFCF dynamics of each spectral component from complex 2DIR spectra. The results show that this new method not only produces equivalent results to more established methodologies in simple spectra but also successfully extracts the FFCF dynamics of individual component from very congested and unresolved 2DIR spectra. In addition, this new methodology can be used to locate the individual frequency components from those complex spectra. Overall, a new methodology for analyzing the 2D spectra is presented here, which allows us to retrieve previously unattainable spectral features from the 2DIR spectra.
超快二维红外（2DIR）光谱学是一种相对较新的方法，现已广泛用于研究溶液中发生的分子过程的分子结构和动力学。通常，在 2DIR 光谱学中，通过在等待时间内观察 2DIR 光谱特征的演化来推断系统的动力学。从 2DIR 得出的最重要的度量之一是频-频相关函数（FFCF），可以使用不同的方法（包括中心和节点线斜率）来提取。但是，这些方法难以正确描述具有多个重叠跃迁的 2DIR 光谱中的动力学。在这里，引入了一种新方法，利用伪泽尼克矩从复杂的 2DIR 光谱中提取每个光谱分量的 FFCF 动力学。结果表明，这种新方法不仅在简单的光谱中产生与更成熟的方法等效的结果，而且还成功地从非常拥挤且未解析的 2DIR 光谱中提取了各个分量的 FFCF 动力学。此外，这种新方法可用于从复杂的光谱中定位各个频率分量。总体而言，这里提出了一种分析 2D 光谱的新方法，该方法使我们能够从 2DIR 光谱中获取以前无法获得的光谱特征。
