Single-Conformation Spectroscopy and Dynamics on Multiple Potential Energy Surfaces: Flexible N-Heterocycle Chromophores and Complexes in Aerosols

在这项由化学系化学结构动力学和机理(CSDM-A)计划资助的项目中，Nathanael Kidwell和他在威廉与玛丽学院的研究团队将使用一系列现代激光技术来研究大气气溶胶中发现的柔性含氮分子(N-杂环)的形状与它们与光的相互作用之间的微妙平衡。N-杂环的形状和与光的相互作用受到溶剂分子存在的强烈影响。了解N-杂环的分子内相互作用以及它们与周围溶剂分子的分子间相互作用，揭示了分子吸收太阳辐射后所遵循的不同路径。在气溶胶中，N-杂环增强了光的吸收和水的蒸发，鉴于气溶胶、云和气候之间的复杂关系，了解这些关键性质是很重要的。为了弄清分子间与溶剂的相互作用，该团队将研究具有明确数量的溶剂分子的柔性N-杂环的分子结构和吸收过程。这种方法将有助于系统地研究从孤立环境到溶剂化环境的分子太阳吸收，以接近液体气溶胶粒子的复杂性。在没有或存在溶剂分子的情况下，每个分子构象的独特性质将用激光光谱工具进行检查，并与几个试图预测形状和吸收结果的理论模型进行比较。PI致力于让高中生成为公民科学家，与当地学校合作，构建一个由Arduino多传感器组成的物联网(IoT)网络，以记录众包大气测量。该项目重点研究柔性N-杂环和取代基水溶络合物的结构、光谱特征和动力学结果，这些取代基会影响咪唑和吡咯单元的电子性质。构象柔性杂环将在超音速喷射膨胀中被分离出来，并使用单构象紫外和红外光谱方法进行探测，以确定化学结构和相关光物理之间的相互作用。在杂环生色团中加入顺序的水分子后，我们将检查其红外和电子光谱，以监测局部溶剂化环境对孤立分子的影响，并探索扩展的氢键网络的拓扑结构。结合单构象光谱实验，受激发射泵浦和速度图成像研究将有助于报告相互竞争的光化学通道和机制。实验观察值将同时与多种理论方法的计算结果进行比较，这些方法包括电子结构方法、从头算分子动力学和机器学习技术。在Kidwell小组指导的学生将获得先进的实验技术和高级理论方法的经验，这些方法探索N-杂环在多个势能表面上的物理性质。该奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

In this project funded by the Chemical Structure Dynamics and Mechanisms-A (CSDM-A) Program of the Chemistry Division, Nathanael Kidwell and his research team at the College of William and Mary will use an array of modern laser techniques to study the delicate balance between the shape of flexible nitrogen-containing molecules (N-heterocycles) found in atmospheric aerosols and their interactions with light. The shape and interactions of N-heterocycles with light are strongly influenced by the presence of solvent molecules. Understanding the intramolecular interactions of N-heterocycles and their intermolecular interactions with surrounding solvent molecules reveals the different pathways the molecules follow after absorption of solar radiation. Within aerosols, N-heterocycles enhance light absorption and water evaporation, key properties that are important to understand given the intricate relationships among aerosols, clouds and climate. To disentangle the intermolecular interactions with the solvent, the team will examine the molecular structure and absorption processes of flexible N-heterocycles with a well-defined number of solvent molecules. This approach will facilitate the systematic investigation of molecular solar absorption from isolated to solvated environments to approach the complexity of liquid aerosol particles. The unique properties of each molecular conformation in the absence or presence of solvent molecules will be examined with laser spectroscopic tools and compared to several theoretical models that attempt to predict the shape and absorption outcomes. The PI is dedicated to engaging high school students as citizen scientists by partnering with local schools to construct an Internet-of-Things (IoT) network of Arduino multisensors to record crowd-sourced atmospheric measurements.This project focuses on the structure, spectroscopic signatures, and dynamical outcomes of flexible N-heterocycles and water-solvated complexes with substituents that influence the electronic character of the base imidazole and pyrrole units. Conformationally-flexible heterocycles will be isolated in a supersonic jet expansion and probed using single-conformation ultraviolet and infrared spectroscopy methods to determine the interplay between chemical structure and the correlated photophysics. Upon sequential water molecule addition to the heterocycle chromophores, the evolving infrared and electronic spectra will be examined to monitor the local solvation environment effects on the isolated molecules and to explore the topology of extended hydrogen-bonded networks. In tandem with the single-conformation spectroscopy experiments, stimulated emission pumping and velocity map imaging studies will serve to report on competing photochemical channels and mechanisms. The experimental observables will be compared simultaneously to the computed results from multiple theoretical approaches, including electronic structure methods, ab initio molecular dynamics and machine-learning techniques. Students mentored in the Kidwell group will gain experience in advanced experimental techniques and high-level theoretical methods that probe the physical properties of N-heterocycles on multiple potential energy surfaces.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.