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1.
在285 nm紫外激光辐照下,用时间分辨电子自旋共振(TRESR)波谱仪研究了对苯醌/乙二醇(PBQ/EG)体系,得到了发射的苯半醌中性自由基PBQH.和乙二醇碳自由基R.(OH)2的CIDEP谱.在化学诱导动态电子极化(CIDEP)基本原理的基础上,建立合理的计算模型,编写相应的程序,对PBQH.和R.(OH)2的CIDEP形成机理进行了定量的解析.通过对不同延时下该体系各种自由基及不同机理成分的对比,明显看出由RPM形成的PBQH.比由TM形成的PBQH.衰减快.这种分析方法可以推广应用于其它体系的CIDEP实验谱的解析.  相似文献   

2.
吩噻嗪-1,4萘醌-乙二醇体系光化学过程的时间分辨ESR研究   总被引:2,自引:2,他引:0  
田秋  陈次平 《波谱学杂志》1998,15(3):205-209
用时间分辨ESR方法研究了吩噻嗪(PTH)-1,4-萘醌(NQ)-乙二醇(RH)体系中的光化学过程.只观察到萘醌的中性半醌自由基NQH*的全发射极化的CIDEP(化学诱导动态极化)信号,并未观察到极化的萘醌负离子NQ·-*的CIDEP信号,表明RH与三重态NQ间的质子转移反应远比PTH与NQ间的电子转移反应为快.NQH·*的CIDEP信号随pH值的变化表明体系中同时有极化自由基NQH·*与NQH·2+*存在,并且其间有质子交换.  相似文献   

3.
用时间分辨电子自旋共振(TR-ESR)和瞬态吸收光谱技术,研究了菲醌在乙二醇均相及其TX-100含水胶束溶液中的光化学反应机理。化学诱导动态电子极化(CIDEP)谱和瞬态吸收光谱都表明,在乙二醇均相溶液中,菲醌光激发三重态3PAQ* 夺取氢原子形成中性自由基PAQH.,三重态机理是CIDEP形成的主要机理。在TX-100含水胶束溶液中,光解主要得到菲醌负离子基PAQ-.,PAQ-.由PAQH.解离形成,解离过程中伴随着极化转移。  相似文献   

4.
利用高时间分辨ESR波谱仪,对苯甲醛为光敏分子的各体系进行了CIDEP(化学诱导动态电子极化)研究,揭示了苯甲醛体系的CIDEP信号的产生过程,并进一步确认了其产生过程中的极化特征.  相似文献   

5.
紫外激光照射下,用时间分辨电子自旋共振(TRESR)波谱仪研究了光解ACETONE/EG体系的化学诱导动态电子极化(CIDEP),得到了丙酮羰自由基(CH3)2C.OH和乙二醇羰自由基CH2OH C.HOH的发射/吸收(E/A)型极化信号,这是一个RPM极化过程.在胶束环境中,不同表面活性剂以及不同的浓度对体系极化的影响是不同的.阳离子表面活性剂CTAB对体系中生成的自由基的极化机理没有产生显著影响,而加入体系中TX-100的浓度对体系的极化机理却产生了很大的影响.在ACETONE/EG体系中,随着TX-100浓度的增加,TM机理对极化强度的贡献明显增大.  相似文献   

6.
285 nm紫外激光照射下,用时间分辨电子自旋共振(TRESR)波谱仪研究了光解丙酮/1,2-丙二醇(ACETONE/PG)体系,得到了丙酮羰自由基(CH3)2.COH和1,2-丙二醇羰自由基CH3.COHCHOH的发射/吸收(E/A)型极化信号,这是一个自由基对(RPM)极化过程。在酸性环境中,溶剂分子的CIDEP谱明显减弱,(CH3)2.COH的CIDEP谱无明显变化,由此可判断光解ACETONE/PG体系是一个夺氢反应;在碱性环境中,(CH3)2.COH反应生成负离子基(CH3)2.CO-.  相似文献   

7.
何光龙 《波谱学杂志》1998,15(3):197-203
用时间分辨ESR测出的吩噻嗪/2,2,6,6-四甲基哌啶氮氧自由基(TEMPO)光诱导产生的三重态发射CIDEP信号可用Blätter提出的自由基-三重态对机理来解释,由荧光光谱及脉冲激光光声微量量热实验结果直接证明了Bläter理论关于自由基只选择淬灭双重自旋态的自由基/三重态对中的三重态的假设.  相似文献   

8.
时间分辨电子自旋共振(TR-ESR)技术是探测和鉴定光化学反应过程中顺磁性中间体的强有力工具,利用TR-ESR技术观察到的化学诱导动态电子极化 (CIDEP) 可以为我们提供丰富的光化学反应机理、反应动力学等信息. 该文较为详细地介绍了CIDEP的4种机理和自行研制的一种零差拍平衡混频的时间分辨ESR波谱仪,总结了TR-ESR技术在光解自由基反应方面的应用.  相似文献   

9.
杜醌自由基光化学路径的CIDEP研究   总被引:1,自引:0,他引:1  
用自制的高时间分辨电子自旋共振波谱仪,测量得到了酸性、碱性和胶束环境下的光解杜醌/乙二醇(DQ/EG)溶液瞬态自由基的化学诱导动态电子自旋极化(CIDEP)谱.在光解均相DQ/EG溶液时,观察到了以增强发射的的中性杜半醌自由基(DQH.)的CIDEP信号;在碱性环境下(pH=9)和TX-100胶束环境下光解DQ/EG体系时得到杜醌负离子自由基(DQ-.)的CIDEP信号;在酸性环境下(pH=2.5)光解DQ/EG体系时,出现的又是中性杜半醌自由基(DQH.)的CIDEP信号.实验结果显示,DQH.由3DQ*与EG之间的氢原子转移反应生成,DQ.-由DQH.的去质子化反应生成,反应中伴随着极化转移.  相似文献   

10.
利用高时间分辨ESR波谱仪研究了二重态自由基和三重态分子之间相互作 用产生的CIDEP(化学诱导动态电子极化),探讨了此类体系中自由基的CIDEP信号的超精细相 关性,认为这种超精细相关性是由于自由基和三重态分子的超精细相互作用引起的。  相似文献   

11.
吩噻嗪-对苯醌体系光化学过程的时间分辨ESR研究   总被引:2,自引:2,他引:0  
报道了用时间分辨电子自旋共振波谱仪对吩噻嗪与对苯醌的乙二醇溶液体系的紫外光照过程进行实时检测,从测得的电子自旋共振极化港可知,电子转移和质子转移在光照过程中同时存在并且相互竞争.  相似文献   

12.
A Fourier transform EPR (FT-EPR) study was made of the photochemistry of [Re(R)(CO)3 (α-diimine)] and [Ru(E)(R)(CO)2(α-diimine)] complexes, where R = alkyl or benzyl, E = I or SnPh3, and α-diimine = 4,4′-dimethyl-2,2′-bipyridine (DMB) orN,N′-diisopropyl-1,4-diazabutadiene (iPr-DAB). Photoexcitation of these complexes leads to homolysis of the metal-alkyl (benzyl) bonds as evident from the detection of the spectra of the alkyl (benzyl) radicals. FT-EPR spectra display strong spin polarization effects attributed to Triplet Mechanism (TM) and Radical Pair Mechanism (RPM) Chemically Induced Dynamic Electron Polarization (CIDEP). CIDEP patterns point to bond dissociation via a triplet state precursor. For a number of complexes, spin polarization was found to exhibit unusually large solvent effects, whereas for one complex the CIDEP pattern proved to be sensitive to the wavelength of laser light used to initiate bond dissociation. These effects reflect the strong dependence of CIDEP on the character of the excited states involved in the photochemical reactions and contribute to the understanding of the reaction mechanism.  相似文献   

13.
Net absorptive CIDEP generation has been demonstrated on singlet molecular oxygen and 4-oxo-2,2,6,6-tetramethyl-1-piperidinyloxyl (OTEMPO) radical system in benzene. CIDEP generation was reasonably explained in terms of the radical-triplet pair mechanism of triplet molecular oxygen-OTEMPO pair with doublet precursor. Several excited molecule-OTEMPO systems have been investigated if this CIDEP generation contributes to their CIDEP spectra. Surprisingly strong CIDEP was produced even in the presence of trace amount of dissolved oxygen, which suggests the importance of complete degassing for CIDEP studies in general systems.  相似文献   

14.
While the photoreduction of quinones has been initially used by us as a model system to probe the role of excited triplet states in CIDEP1 and CIDNP2 phenomena, our continuing interest in the quinone photochemical systems is partly due to their photobiological importance. Alkyl substituted quinones have in fact been shown to be associated with chlorophyll3 and to be involved in photosynthesis4. The 2-methyl-p-benzoquinone (MQ) is the simplest unsymmetrical alkyl substituted p-quinone which, during photolysis, may lead to two isomeric semiquinone radicals. We are particularly interested in applying the CIDEP and CIDNP techniques to investigate the structure and reactivity of the intermediate semiquinone radicals as they may give some insight to the photochemical properties of the parent 2-methyl-p-quinone.  相似文献   

15.
Quenching of the triplet excited state of molecular tryptophan by nitroxide radical in 1,4-dioxane and water solutions was investigated by means of time-resolved electron paramagnetic resonance (EPR) and Fourier-transform (FT)-EPR. The chemically induced dynamic electron polarization (CIDEP) signals with net emissive phase were recorded at these quenching events and were analyzed through radical-triplet pair mechanism. The CIDEP time profiles were well reproduced by Bloch and kinetic equations, assuming radical-triplet pair mechanism with the appropriate quenching rate constants. From a comparison of the simulation and the experiment, CIDEP enhancement factor in 1,4-dioxane was determined to be −30 × P eq, where P eq is the spin polarization of nitroxide at thermal equilibrium. Net emissive CIDEP was also observed by FT-EPR measurements on the nitroxide quenching of the triplet excited state of tryptophan residue in α-lactalbumin. Magnitude of CIDEP created in α-lactalbumin/nitroxide system depends on the pH condition of α-lactalbumin solution, which is related to protein folding dynamics. We argue the CIDEP mechanism at the α-lactalbumin surface and propose a possibility of a novel CIDEP method to probe a protein surface and structural changes.  相似文献   

16.
The radical-triplet pair mechanism for chemically induced dynamic electron polarization (CIDEP) created in the quenching of excited state molecules by free radicals is explained on the basis of recent time-resolved electron spin resonance spectroscopic results and theoretical studies. The CIDEP of 2,2,6,6-tetramethylpiperidinyl-1-oxyl (TEMPO) and galvinoxyl radicals exhibit various CIDEP patterns of net and mutliplet types and CIDEP phases of absorption and emission. The CIDEP patterns are described by the quartet-doublet state mixings within the radical-triplet encounter pairs. The mixings by the spin-dipolar and the hyperfine interactions are responsible for the net and the multiplet patterns, respectively. The factors controlling the CIDEP phases are the spin multiplicity of the excited state quenched by radicals and the sign of the intermolecular exchange interaction of the radical-triplet encounter pairs. In particular, the intermolecular charge transfer effect on the exchange interaction is discussed much in detail from the viewpoints of CIDEP magnitudes and phases. A CIDEP creation in the O2(1Δg)-TEMPO system is also introduced and is described by the radical-triplet pair mechanisms. Applications of this CIDEP used as a probe of O2(1Δg) in condensed phase are mentioned.  相似文献   

17.
The photochemical reactions of methylene blue (MB) included in water-soluble sulfonated calix[n]arenes (n = 4, 6, 8) are studied using a time-resolved electron spin resonance method. The chemically induced dynamic electron polarization (CIDEP) spectra show the formation of the complex radical pair composed of the MB monocation radical and calixarene (phenoxyl-type) radical. The lifetime and broadened spectral shape are dependent on the size of the calixarene and are due to the longitudinal and transverse relaxation mainly induced by the tumbling motion of the radical pair with the spin dipole–dipole interaction. The pair dissociates in a few hundreds of nanoseconds in cases of n = 6 and 8.  相似文献   

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