Non-Minimum Energy Pathways in the Dissociation of Energy-Selected Ions

在这个由化学系化学结构、动力学和机制(CSDM-A)计划资助的项目中，太平洋大学的Bálint Sztáray教授和Anthony Dutoi教授正在研究电子被紫外光移除后分子分解的方式。直到最近，化学家们还认为这些过程几乎完全由势能面控制，类似于寻找穿过山脉的最低通道。最近，人们了解到，参与原子探索以前未被识别的反应路径或在低能量路径之间切换并不少见。有时甚至没有一条明显独特的路径，原子在反应完成之前花了大量的时间“漫游”。这个项目结合了实验和计算方法来回答这样的基本问题，如能量如何在碎裂的离子中流动，什么分子水平的参数控制反应的结果，以及反应机制如何/何时违反传统逻辑。这项研究涉及加州中央山谷的本科生和研究生，他们通常是家里第一个获得大学学位的人。该项目为他们提供了先进的实验和理论技能，使他们能够在高科技就业市场上很好地定位。非最小能量路径(Non-Minimum-Energy-Path，Non-MEP)机制，如非统计动态效应、反应路径分叉和漫游，可能导致反应产物中异常的分支比和异常的内部和动能分布。本项目使用光电子光离子符合谱(PEPICO)研究能量选择气相离子中涉及非MEP现象的单分子解离。这些仪器由Sztáray教授及其合作者建造，可以测量稳定和不稳定的、热的和分子束冷却的物种，并可以收集MEV分辨率的分支、单分子速率和动能释放数据。实验研究得到了杜托伊教授的分子动力学轨迹计算的补充，以阐明它们的机制，并通过在选定点处的高水平量子化学计算进一步扩展。从一开始就将实验与计算模型和理论相结合，可以提取以前仅通过实验或理论无法获得的物理见解。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 Division of Chemistry, Professors Bálint Sztáray and Anthony Dutoi at the University of the Pacific are investigating the ways that molecules break apart after an electron is removed by ultraviolet light. Until recently, chemists thought of these processes as being controlled almost entirely by the potential energy surface, akin to looking for the lowest pass through mountains. More recently, it was learned that it is not uncommon for the participant atoms to explore previously unrecognized reaction paths or switch between low-energy paths. Sometimes there is not even a clearly unique path, with the atoms spending significant amounts of time “roaming” before the reaction completes. This project combines experimental and computational methods to answer such fundamental questions as how energy flows in the fragmenting ion, what molecular-level parameters govern outcomes of reactions, and how/when reaction mechanisms defy conventional logic. The research involves undergraduate and graduate students from California’s Central Valley who are often the first in the family to get a university degree. This project provides them with advanced experimental and theoretical skills to position them well on the high-tech job market.Non-minimum-energy-pathway (non-MEP) mechanisms, such as nonstatistical dynamic effects, reaction path bifurcations, and roaming, can lead to unusual branching ratios and unusual distributions of internal and kinetic energy in reaction products. This project uses Photoelectron Photoion Coincidence (PEPICO) spectroscopy to investigate unimolecular dissociations involving non-MEP phenomena in energy-selected gas-phase ions. The instruments, built by Professor Sztáray and collaborators, enable measurement of both stable and unstable, thermal and molecular-beam-cooled species, and allow collection of branching, unimolecular rate, and kinetic energy release data with meV resolution. The experimental studies are complemented by Professor Dutoi’s molecular dynamics trajectory calculations to elucidate their mechanisms, further extended by high-level quantum-chemical calculations at select points. Integrating experimentation with computational modeling and theory from the onset allows extraction of physical insights not previously attainable by either experiment or theory alone.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.