Charge Resonance Interaction in Aromatic Clusters

我们建议探测电荷共振（CR）相互作用的冷芳族簇离子在气相中孤立的质谱，红外和电子激光光谱，和量子化学计算。CR基于电荷离域，是一种强的基本分子间力，补充了带电簇中的其他吸引力，如静电力、感应力（极化力）和色散力。由于其重要性，CR已被广泛表征在低分辨率的凝聚相。然而，气相研究-不受环境的强烈扰动-到目前为止仅限于质谱和光谱，这两者都不能提供有关CR强度和所涉及的电荷分布的精确和直接的信息。在此，我们提出了一种新的方法，在该方法中，我们利用高分辨率的红外光谱的冷和质量选择的芳香族簇阳离子在气相中的CR相互作用（结构，能量，动力学）的中心属性探测在高精度相关的强度与振动频率的变化的CR。值得注意的是，这种方法使我们能够第一次实验评估的CR的强度和电荷离域的程度在孤立的芳香族簇离子在高精度。这种结合实验和计算的方法最近已经开创了由我们组的吡咯二聚体阳离子的情况下，基准，现在应扩展到一个更普遍和系统的表征的CR在各种芳香族簇离子，以提供新的和可靠的洞察其性能在分子水平上。为此，我们将研究CR的强度和动力学对各种参数的依赖性，包括（1）极性和非极性配体的微溶剂化（对称性破坏和恢复、微扰类型和强度的变化），（2）吡咯官能团的取代以及一个吡咯被另一个芳香分子取代（电离能的变化），和（3）CR在较大的吡咯簇中的离域。我们还将探讨各种能量分解分析方案的应用，以评估对CR的各种贡献。

We propose to probe the charge resonance (CR) interaction in cold aromatic cluster ions isolated in the gas phase by means of mass spectrometry, infrared and electronic laser spectroscopy, and quantum chemical calculations. CR is based on charge delocalization and is a strong fundamental intermolecular force that complements other attractive interactions in charged clusters such as electrostatic, induction (polarization), and dispersion forces. Because of its importance, CR has been characterized extensively at low resolution in the condensed phase. However, gas-phase studies - which do not suffer from strong perturbations of the environment - have so far been restricted to mass spectrometry and optical spectroscopy, both of which do not provide precise and direct information about the strength of the CR and the involved charge distribution. Herein, we propose a new approach in which we utilize high-resolution infrared spectroscopy of cold and mass-selected aromatic cluster cations in the gas phase to probe the central properties of CR interaction (structure, energetics, dynamics) at high precision by correlating the strength of the CR with vibrational frequency shifts. Significantly, this approach enables us for the first time to experimentally evaluate the strength of the CR and the degree of charge delocalization in isolated aromatic cluster ions at high precision. This combined experimental and computational approach has recently been pioneered and benchmarked by our group for the case of the pyrrole dimer cation and shall now be extended to a more general and systematic characterization of the CR in a variety of aromatic cluster ions to provide new and reliable insight into its properties at the molecular level. To this end, we will investigate the dependence of the strength and dynamics of the CR on a variety of parameters, including (1) microsolvation by polar and nonpolar ligands (symmetry breaking and restoring, variation of type and strength of perturbation), (2) substitution of functional groups of pyrrole and substitution of one pyrrole by another aromatic molecule (change in ionization energy), and (3) delocalization of CR in larger pyrrole clusters. We will also explore the application of various schemes of energy decomposition analysis to evaluate the various contributions to the CR.