Photodissociation Dynamics of Small Molecules: Collisionless and Collisional Processes

南加州大学的汉娜·赖斯勒得到了实验物理化学计划的支持，继续她对开壳分子物种的单分子和双分子动力学的研究，例如自由基和电子激发的分子，这些分子通过多条路径反应。与大气中的过程有关的分子和自由基的光引发单分子分解将被研究，重点是非绝热转变、竞争路径、相关分布以及分支比与激发能量的关系。状态对状态的研究将扩展到更大的分子，这在各种环境中很重要，在这些环境中，路径由几个多维势能面控制。光碎片速度图成像技术将被开发和进一步发展，以在质量、频率、速度和角域提供同时的乘积分辨率。选择用于光解离研究的体系包括卤甲基和三氧化二氮自由基，以及弱结合物种，如一氧化氮二聚体。此外，红外激光诱导的氨二聚体(如氨-卡宾和氨-乙炔)的振动预解离也将通过成像技术进行检测。激光和探测方法的最新进展为理解具有潜在环境和技术重要性的复杂化学反应系统提供了技术能力。目前的努力利用这些新技术，以微观细节检查分子的化学，当能量通过光的吸收添加到分子中时，这些分子可以通过竞争路径进行反应。这一研究项目还有望为研究生和博士后助理提供反应动力学的实验和理论基础方面的广泛培训。

Hanna Reisler of the University of Southern California is supported by the Experimental Physical Chemistry Program to continue her studies of the unimolecular and bimolecular dynamics of open shell molecular species such as free radicals and electronically excited molecules that react via multiple pathways. Photoinitiated unimolecular decomposition of molecules and radicals relevant to processes in the atmosphere will be examined, emphasizing nonadiabatic transitions, competitive pathways, correlated distributions, and the dependence of branching ratios on excitation energy. State-to-state studies will be extended to larger molecules, important in a variety of environments, where pathways are controlled by several multidimensional potential energy surfaces. The photofragment velocity map imaging technique will be exploited and further developed to afford simultaneous product resolution in the mass, frequency, velocity, and angular domains. The systems chosen for photodissociation studies include halomethyl and nitrogen trioxide radicals, and a weakly bound species such as nitric oxide dimers. As well, infrared laser-induced vibrational predissociation of ammonia dimers (such as ammonia-carbene and ammonia-acetylene) will be examined by imaging techniques. Recent advances in laser and detection methodologies are providing the technical capability to achieve understanding of complex chemical reaction systems that have potential environmental and technological importance. The present effort capitalizes on these new technologies, to examine in microscopic detail the chemistry of molecules that can react by competing pathways when energy is added to them by the absorption of light. This research project is additionally expected to provide broad training for graduate students and postdoctoral associates in the experimental and theoretical foundations of reaction dynamics.