分子和自由基的同步辐射光电子光离子符合实验研究

发布时间：2018-01-04 06:36

本文关键词：分子和自由基的同步辐射光电子光离子符合实验研究　出处：《中国科学技术大学》2017年博士论文　论文类型：学位论文

【摘要】：自由基是大气化学反应中重要的中间体,其浓度低、种类繁多,对理论和实验都提出了极大的挑战,目前大气化学反应及相关理论计算中迫切需要的自由基的能级和结构等重要数据还十分缺乏。同步辐射阈值光电子光离子符合质谱(Synchrotron threshold photoelectron photoion coincidence time-of-flight mass spectrometry)充分发挥同步辐射真空紫外光源、符合质谱和阈值光电子谱等技术的优点,同时检测分子及自由基光电离过程中产生的阈值光电子和光离子,并进行符合测量,是开展有机化合物分子及相关自由基光电离研究的有效方法。本论文研究工作采用合肥同步辐射光源和阈值光电子光离子符合成像质谱仪,开展了若干分子及相关自由基的光电离和光电离解离等实验研究,精确测量了分子及自由基的电离能、碎片离子出现势等基本数据,获得了分子及自由基的光谱、能级结构及动力学等信息,为相关理论计算、深入研究大气化学反应机理等提供重要数据和科学依据。本论文的研究内容主要包括以下几个部分:1.甲基自由基的阈值光电子谱实验研究。基于连续超声分子束技术,搭建了一套闪速热解反应装置,用于在实验室中高效、稳定地产生自由基,并开展有机化合物的高温热解反应等实验研究。以最简单的甲基自由基(CH_3)作为示范研究体系,通过前体物CH_3NO_2分子的闪速热解制备出CH_3自由基,结合同步辐射阈值光电子光离子符合成像质谱仪开展了 CH_3自由基的阈值光电子谱实验研究。通过检测具有质量选择的阈值光电子谱,精确测量获得了 CH_3自由基的绝热电离能,其值为9.84±0.01 eV,并对闪速热解及光电离过程中CH_3自由基的振动激发模式进行了分析和标定。2.正丁烷分子的闪速热解反应研究。采用同步辐射阈值光电子光离子符合成像质谱仪和闪速热解装置,我们开展了正丁烷分子(n-C_4H_(10))的闪速热解反应研究。实验中通过采集阈值光电子光离子符合质谱,首次成功检测获得n-C_4H_(10)热解反应中的C3H7自由基瞬态中间产物。结合具有质量选择的阈值光电子谱,精确测量了 C_2H_5自由基的绝热电离能和垂直电离能,其值分别为8.20±0.01 eV和8.70±0.01 eV,并观察到了 C_2H_5自由基光电离过程中的振动模跃迁激发;精确测量了热解产物C_3H_6分子的绝热电离能,9.75±0.01eV,并对C_3H_6光电离过程中的碳碳双键(C==C)伸缩振动激发进行了标定。此外,结合高精度量化计算获得了 n-C_4H_(10)热解反应的势能面,对n-C_4H_(10)热解反应路径上的过渡态结构进行了结构分析,并对其热解反应机理进行了研究。3.正丁烷分子的光电离解离实验研究。利用同步辐射阈值光电子光离子符合成像质谱仪,开展了 n-C_4H_(10)分子的光电离解离实验研究,通过分别检测n-C_4H_(10)+母体离子和C_3H_7~+碎片离子的阈值光电子谱,测量获得了 n-C_4H_(10)分子的电离能和C_3H_7~+碎片离子出现势。此外,通过阈值光电子谱构建了 Breakdown曲线,并对其进行了拟合,以扣除分子内能等因素的影响,精确测量获得了 C_3H_7~+碎片离子的绝热出现势,11.31 ±0.01 eV。4.p-,m-,o-C_7H_7Br同分异构体分子的光电离解离实验研究。同分异构体具有相同的分子式,但具有不同的化学结构和性质,一直是研究的热点和难点问题。本文以C_7H_7Br作为示范体系,探讨阈值光电子光离子符合技术在同分异构体光电离检测及研究方面的应用。通过改变同步辐射光的能量,在阈值光电子光离子符合质谱中分别观察到了 p-,m-,o-C_7H_7Br+母体离子和相应的C_7H_7+碎片离子。通过检测具有质量选择的阈值光电子谱,精确测量了 p-,m-,o-C_7H_7Br同分异构体分子的电离能(8.68±0.01 eV,8.82土0.01 eV 和 8.78±0.01 eV),以及相应C_7H_7+碎片离子的出现势(11.46±0.01eV,11.55±0.01eV 和 11.40±0.01eV)。同时,结合量子化学计算,对p-,m-,o-C_7H_7Br光电离解离反应过程进行了分析,其解离主要是通过C-Br键的断裂来产生具有甲苯基构型的C_7H_7+碎片离子。
[Abstract]:Free radicals are important intermediates in the chemical reaction in the atmosphere, its low concentration, variety, have posed a great challenge to the theory and experimental data, an important urgent need to calculate the atmospheric chemistry and the related theory of free radical level and structure. There is also a lack of synchrotron radiation light ion mass spectrometry with threshold photoelectron (Synchrotron threshold photoelectron photoion coincidence time-of-flight mass spectrometry) make full use of synchrotron radiation light source, with advantages of mass spectrometry and threshold photoelectron spectroscopy technology, and produce molecular detection and free radical photoionization process of threshold photoelectron and photoion coincidence measurement, and, is an effective method to investigate molecular organic compounds and free radical light ionization. This thesis uses Hefei synchrotron radiation light source and light ion with threshold photoelectron Imaging spectrometer, carried out experimental research on several molecules and free radicals from photoelectric and optical ionization and dissociation ionization, accurate measurement of molecules and free radicals, ions appear potential and other basic data, the spectrum obtained by molecular and free radicals, energy structure and dynamics information, calculation theory, provide important data and scientific basis for the in-depth study of the atmospheric chemical reaction mechanism. The main contents of this thesis include the following parts: Experimental Study on spectra of 1. threshold photoelectron methyl radicals. Continuous supersonic molecular beam technique based on a set of flash pyrolysis reactor for high efficiency in the laboratory, produce a stable free radical, and carry out the pyrolysis reactions of organic compounds such as methyl radicals in experimental study. The simplest (CH_3) as a demonstration research system by flash pyrolysis precursor of CH_3NO_2 molecule The preparation of CH_3 free radicals, combined with synchrotron radiation to carry out CH_3 free radical threshold photoelectron spectrum experimental study of imaging mass spectrometer threshold photoelectron light ion line. By detecting the quality of selected has the threshold photoelectron spectrum, obtained the accurate measurement of adiabatic ionization of CH_3 radicals, and its value is 9.84 + 0.01 eV, and the flash pyrolysis and photoionization of CH_3 free radical in the process of vibration excitation pattern of flash pyrolysis reaction analysis and calibration of.2. butane molecules. By using synchrotron radiation photoelectron photoion coincidence imaging threshold mass spectrometer and flash pyrolysis device, we carried out molecular n-butane (n-C_4H_ (10)) of the flash pyrolysis reaction experiments through research. The acquisition threshold photoelectron light ion with mass spectrometry, first successful detection of n-C_4H_ (10) C3H7 free radical intermediates in the transient pyrolysis reaction. Combined with the quality threshold selection The photoelectron spectrum, accurate measurement of the adiabatic ionization of C_2H_5 radicals and vertical ionization energy, the values were 8.20 + 0.01 and 8.70 + 0.01 eV eV, and observed the vibration mode transitions of C_2H_5 free radical photoionization process excitation; adiabatic ionization energy of pyrolysis products of C_3H_6 molecular measurement accuracy, 9.75 + 0.01eV, and the carbon carbon double bond C_3H_6 photoionization process (C==C) stretching excitations are analyzed. In addition, combined with the high precision quantitative calculation to get n-C_4H_ (10) surface of pyrolysis reaction of n-C_4H_ (10) structure transition state reaction path on pyrolysis were analyzed, and the photoelectric pyrolysis the reaction mechanism of.3. n-butane molecules from dissociation experiments. Using synchrotron radiation photoionization threshold photoelectron coincidence imaging mass spectrometry, n-C_4H_ (10) to carry out the experimental study of molecular photoionization dissociation, were detected through n-C_4H_ (10) C_3H_7~+ + threshold photoelectron parent ion and fragment ion spectrum measurement was n-C_4H_ (10) ionization energy and C_3H_7~+ ions appear potential. In addition, the threshold photoelectron spectrum to construct the Breakdown curve, and has carried on the fitting effect to deduct the intramolecular can and other factors, to obtain accurate measurement the adiabatic C_3H_7~+ ions appear potential, 11.31 + 0.01 eV.4.p-, m-, o-C_7H_7Br optical isomers from dissociation experiments. Isomers with the same molecular formula, but has the chemical structure and the properties of different, has always been a hot and difficult research problem. This paper uses C_7H_7Br as the demonstration system to investigate, threshold photoelectron technology in line with the application of ion optical isomers of photoionization detection and research. By changing the synchrotron radiation energy spectrum, in crude in the threshold photoelectron photoion character Don't observed p-, m-, o-C_7H_7Br+ and corresponding C_7H_7+ fragments of the parent ion ion. By detecting the quality of selected has the threshold photoelectron spectrum, the accurate measurement of p-, m-, o-C_7H_7Br ionization isomers can (8.68 + 0.01 eV, 8.82 eV and 8.78 + 0.01 + 0.01 eV), and the corresponding C_7H_7+ fragment ion potential (11.46 + 0.01eV, 11.55 + 0.01eV and 11.40 + 0.01eV). At the same time, combined with quantum chemical calculations of p-, m-, o-C_7H_7Br photoionization and photodissociation reaction process are analyzed, which is mainly caused by the dissociation of C-Br bond cleavage with C_7H_7+ fragment ions tolyl configuration.

【学位授予单位】：中国科学技术大学
【学位级别】：博士
【学位授予年份】：2017
【分类号】：P402;O621.1

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