1,2,4-三甲苯及邻碘甲苯分子激发态超快动力学的研究

发布时间：2018-05-07 13:15

本文选题：激发态动力学 + 光电子影像　；参考：《中国科学院研究生院(武汉物理与数学研究所)》2016年博士论文

【摘要】：分子激发态动力学过程在环境科学、生命科学、材料科学等领域发挥着重要作用,比如臭氧层的形成和保持、光合作用、分子开关等。分子激发态动力学过程包含发光、内转换、系间交叉、振动弛豫、解离、异构等,这些过程发生的时间尺度大都在皮秒至飞秒量级。飞秒时间分辨的质谱技术和飞秒时间分辨的光电子影像技术具有飞秒量级的时间分辨能力,很适合用于实时跟踪分子激发态动力学演化过程。本文利用飞秒时间分辨光电子影像技术研究了1,2,4-三甲苯分子的超快内转换动力学过程,利用飞秒时间分辨的质谱技术研究了邻碘甲苯分子的解离动力学过程。1,2,4-三甲苯及邻碘甲苯是化工和生物合成中最为常见的分子,了解它们的光物理光化学反应机理有助于我们认识和理解它们在化工和生物合成中的反应机理。本论文的主要研究工作有：(1)1,2,4-三甲苯分子的S2→S1态超快内转换动力学过程研究。实验中1,2,4-三甲苯分子吸收两个400 nm的光子后被激发到S2态。通过光电子能谱上三个特征光电子能谱带的强度随泵浦-探测延迟时间的变化,实时观察到1,2,4-三甲苯分子S2→S1态的超快内转换动力学过程。通过监控母体离子信号随泵浦-探测延迟时间的变化,我们测得S2态的衰减寿命约为72 fs,通过S2态内转换过程而布居的热振动Sl态的寿命约为16.4 ps。和之前人们对苯、甲苯、二甲苯分子的研究结果比较发现,甲基的取代数目越多,S1态的寿命越长,可能是因为甲基的取代阻碍了分子从S1态演化到S1/S0的锥形交叉区,从而使寿命变长。(2)邻碘甲苯分子的光解动力学研究。实验中邻碘甲苯分子吸收一个266 nm的光子后被同时激发到具有束缚态特征的ππ*态和具有排斥态特征的no*态上。利用强800 nm光作为探测光,通过多光子电离的方法实时跟踪解离过程。通过记录母体离子信号及解离生成的碎片信号随泵浦-探测延迟时间的变化,我们发现,邻碘甲苯分子的激发态衰减过程是一个非常快的过程,时间尺度约为100 fs,反映的是初始布居πσ*态的衰减动力学,同时还在解离碎片信号上观察到了一个上升组分,它反映的是邻碘甲苯分子的光解动力学过程,时间尺度约为380 fs。此外,我们利用基态碘原子的共振波长298.23nm作为探测光,利用共振多光子电离的方法选择性地探测了解离生成基态碘原子的解离通道,测得生成基态碘原子的平均解离时间约为400 fs。
[Abstract]:The kinetic process of molecular excited states plays an important role in the fields of environmental science, life science and material science, such as the formation and maintenance of the ozone layer, photosynthesis, and molecular switches. The kinetic processes of molecular excited states include luminescence, internal conversion, intersystem cross, vibrational relaxation, dissociation, isomerism and so on. The time scale of these processes is large. Both from picosecond to femtosecond order of time. Femtosecond time resolved mass spectrometry and femtosecond time resolved photoelectron imaging technology have the time resolution ability of the femtosecond order of time. It is very suitable for real-time tracking of the dynamic evolution process of molecular excited states. In this paper, the 1,2,4- three toluene molecule is studied by the femtosecond time resolved photoelectron image technology. The kinetic process of fast internal conversion, using femtosecond time resolved mass spectrometry to study the dissociation kinetics of O iodide molecules,.1,2,4- tri trimethyl benzene and O iodide are the most common molecules in chemical and biosynthesis. Understanding the mechanism of their photometric chemical reactions helps us to understand and understand them in chemical and biological processes. The main research work in this paper is: (1) the study of the ultrafast internal conversion kinetics of S2 to S1 states of 1,2,4- three toluene molecules. In the experiment, the 1,2,4- three toluene molecule absorbs two 400 nm photons and is excited to the S2 state. The intensity of the photoelectron energy spectrum band on the photoelectron spectroscopy is delayed by the pump detection delay. The ultrafast internal conversion process of the 1,2,4- three toluene molecule S2 to S1 state is observed in real time. By monitoring the change of the pump detection delay time, the decay life of the S2 state is measured to be about 72 FS, and the lifetime of the thermal vibrational Sl state in the S2 state transition process is about 16.4 PS. and the people before it. The results of the study of benzene, toluene and xylene found that the longer the number of methyl substituted, the longer the lifetime of the S1 state, may be because the replacement of the methyl group hindered the evolution of the molecule from the S1 state to the conical cross region of the S1/S0, thus making the life longer. (2) the photodissociation kinetics of the o-ioditoluene molecule. The 266 nm photons are stimulated at the same time in the no* state with the characteristic of the bound state and the characteristic of the rejection state. Using the strong 800 nm light as the detection light, the dissociation process is tracked through the multiphoton ionization method. By recording the changes of the matrix ion signal and the dissociated fragment signal with the pump detection delay time, we It is found that the decay process of the excited state of the o iodide molecule is a very fast process, the time scale is about 100 fs, reflecting the decay kinetics of the initial pion sigma state, and also a rising component is observed on the dissociated fragment signal, which reflects the photodissociation kinetics of the o iodide molecule, with a time scale of about 380 FS. In addition, we use the resonance wavelength 298.23nm of the ground state iodine atom as the detection light, using the resonance multiphoton ionization method to selectively detect the dissociation channel of the iodine atoms from the ground state, and the average dissociation time of the generated ground state iodine atom is about 400 fs..

【学位授予单位】：中国科学院研究生院(武汉物理与数学研究所)
【学位级别】：博士
【学位授予年份】：2016
【分类号】：O561

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