State-to-State Photodissociation of Polyatomic Free Radicals: Nonadiabatic Dynamics and Quantum Coherence

化学部化学结构、动力学与机理A （CSDM-A）项目资助美国加州大学河滨分校张劲松教授研究多原子自由基的光解动力学。自由基是许多化学环境（如燃烧和大气化学）中重要的反应中间体。本研究旨在了解多原子自由基的光化学性质以及相互作用的电子态对量子精度的影响。从这个项目中获得的知识（自由基电子结构、能量学、反应机理等）对燃烧、大气化学、理论化学和物理界都是有价值的。该项目培训研究生，为他们在学术界或工业界的职业生涯做好准备，并促进女性和代表性不足的少数民族本科生的研究经验。该项目涉及河滨和圣贝纳迪诺社区学院的不同学生群体。该项目还指导经济困难的高中生进行暑期研究实习。该项目主要研究羟基甲基、氢过氧和亚甲基自由基。在实验中，自由基是由合适的前体光解和随后的反应产生的，并在具有明确初始能量的分子束中冷却。在可调激光辐射下，自由基在单次碰撞条件下光解离，产生氢原子光产物。利用高n里德伯原子飞行时间技术测量了状态分辨产物的动能和角分布。这些分布与理论计算密切相关，是理解光解动力学和机制的核心。这项研究产生了高质量的数据和基准，以测试受激开壳物种的量子力学理论。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

The Chemical Structure, Dynamics and Mechanisms A (CSDM-A) program of the Chemistry Division funds Professor Jingsong Zhang of the University of California at Riverside to investigate the photodissociation dynamics of polyatomic free radicals. Free radicals are important reactive intermediates in many chemical environments (such as combustion and atmospheric chemistry). This research aims to understand the photochemistry of polyatomic radicals and the roles of interacting electronic states with quantum accuracy. The knowledge (free radical electronic structures, energetics, reaction mechanisms, etc.) from this project is valuable to the combustion, atmospheric chemistry, theoretical chemistry, and physics communities. The project trains graduate students and prepares them for careers in academia or industry and promotes research experience of women and underrepresented minority undergraduate students. The project reaches out to the diverse student population in the Riverside and San Bernardino community colleges. This program also mentors economically disadvantaged high school students for summer research internships.The project focuses on the hydroxymethyl, hydroperoxy, and methylene radicals. Experimentally, the free radicals are produced by photolysis of suitable precursors and subsequent reactions and are cooled in a molecular beam with a well-defined initial energy. The free radicals are photodissociated under a single collision condition by tunable laser radiation, producing hydrogen atom photoproducts. The high-n Rydberg atom time-of-flight technique is utilized to measure state-resolved product kinetic energy and angular distributions. These distributions are closely related to theoretical calculations and are central to understanding photodissociation dynamics and mechanisms. The research generates high-quality data and benchmarks to test quantum mechanical theories of the excited open-shell species.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.