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Steering chemical branching in photodissociation of molecules in a high vibrational overtone by combining laser and synchrotron radiation

通过结合激光和同步加速器辐射，以高振动泛音引导分子光解离中的化学分支

基本信息

批准号：
14340188
负责人：
MITSUKE Koichiro
金额：
$ 8.06万
依托单位：
The Institute for Molecular Science (2004)Okazaki National Research Institutes (2002-2003)
依托单位国家：
日本
项目类别：
Grant-in-Aid for Scientific Research (B)
财政年份：
2002
资助国家：
日本
起止时间：
2002 至 2004
项目状态：
已结题

项目摘要

Initial vibrational excitation in molecules may influence the chemical branching in photodissociation, if two or more different dissociation pathways are accessible from an electronically excited state. Much attention has been focused on the work of Crim, who could accomplish the selective bond-breaking of heavy water, HOD. We are planning to use synchrotron radiation (SR) to promote vibrationally excited molecules to electronically excited states in the vacuum UV region. The main objective is to elucidate the properties of dissociative states by sampling a wide range of their potential energy surfaces, such as dynamics determining the final-state distributions of the products, nonadiabatic transitions on dissociation, and assignments and characterization of unknown multiply-excited states produced by Auger decay. We have developed an experimental system for laser-SR two photon ionization the crux of which are an ultrahigh resolution continuous titanium-sapphire laser and beam alignment devices for strict overlapping of the two photon beams. The apparatus was connected to a beam line of the Photon Factory in Tsukuba. The wavenumber of the laser was determined precisely by observing photoacoustic signal from laser excited H2O measured with a lock-in modulation technique. The photon beam alignment devices are situated upstream and downstream of a central photoionization chamber. Each device is comprised of two SUS plates fitted on two-dimensional motion feedthroughs. These plates can be inserted across the photon beam axis without breaking the system vacuum, which permits us to easily attain good spatial overlap of the two beams. The OH+ ions produced via dissociation of H2O*(4νO-H)+hν→OH+(Χ3Σ-)+H(n=1)+e- were detected by time-of-flight mass spectrometry at SR photon energies near the dissociation threshold of 18.05 eV with respect to the neutral ground state of water.

如果一个电子激发态有两条或两条以上不同的解离路径，分子中的初始振动激发可能会影响光解的化学分支。CRIM的工作一直受到人们的关注，他可以实现重水的选择性断键，HOD。我们计划使用同步辐射(SR)在真空紫外区将振动激发的分子提升到电子激发态。主要目的是通过对解离态的各种势能面进行采样来阐明它们的性质，例如决定产物终态分布的动力学、解离时的非绝热跃迁以及由俄歇衰变产生的未知多激发态的归属和表征。我们研制了一套激光-SR双光子电离实验系统，其关键是超高分辨率的连续钛宝石激光器和两束光子严格重叠的光束对准装置。该装置被连接到筑波的光子工厂的光束线上。用锁定调制技术测量了激光激发水的光声信号，精确地确定了激光的波数。光子束对准装置位于中央光电离室的上游和下游。每个装置由安装在二维运动馈线上的两个SUS板组成。这些平板可以在不破坏系统真空的情况下穿过光子束轴线插入，这使得我们可以很容易地获得两束光的良好空间重叠。用飞行时间质谱仪检测到H2O*(4νO-H)+hν→OH+(Χ3Σ-)+H(n=1)+e-的解离产生的OH+离子，其SR光子能量相对于水的中性基态的解离阈值为18.05 eV。