安息香及其衍生物光反应的CIDNP研究

本文用光照的¹H化学诱导动态核极化技术,研究了安息香及其衍生物的光化反应。并通过不同浓度的自由基捕获剂(PBN)的加入,对所研究体系的CIDNP效应的影响,分析推断了安息香等的光解及其光解自由基的复合的反应机理。并讨论了双取代安息香醚的光反应机理随取代基的变化而有所不同。     

双环戊二烯-氯醌体系的CIDNP研究

利用Nd/YAG激光器的三倍频激光脉冲(355nm),对双环戊二烯的光敏化反应进行了CIDNP方面的研究,结合CIDNP理论模拟谱的计算,证实了Roth等人所推测的此光敏化反应自由基中间体结构为双重的烯丙基物种,通过计算,确定了自由基各质子的超精细偶合常数hfc的相对大小和绝对符号以及各碳原子上的未偶电子自旋密度,从而对这个特殊的自由基中间体结构有了更清晰的认识.     

双环戊二烯-氯醌体系的CIDNP研究

利用Nd/YAG激光器的三倍频激光脉冲(355nm),对双环戊二烯的光敏化反应进行了CIDNP方面的研究,结合CIDNP理论模拟谱的计算,证实了Roth等人所推测的此光敏化反应自由基中间体结构为双重的烯丙基物种,通过计算,确定了自由基各质子的超精细偶合常数hfc的相对大小和绝对符号以及各碳原子上的未偶电子自旋密度,从而对这个特殊的自由基中间体结构有了更清晰的认识.     

N2O+离子A2∑+电子态的光谱研究

用一束波长为360.55 nm的激光,通过N2O分子的(3+1)共振增强多光子电离过程制备纯净的母体离子N2O+X2Ⅱ3/2,1/2(000).用另一束可调谐激光将N2O+离子激发至预解离态A2Σ+,利用飞行时间质谱检测解离碎片NO+离子强度随光解光波长的变化,在278-328 nm波长范围内获得了光解碎片的激发(PHOFEX)谱.观测到了N2O+离子A2Σ+←X2Ⅱ电子跃迁较丰富的振动谱带.通过对PHOFEX光谱的标识,获得了A2∑+态较准确和全面的分子光谱常数.     

分光技术在自由电子激光结合里德堡态氢原子飞行时间谱装置中的应用（英文）

木文描述了一种应用于自由电子激光结合高里德堡态氢原子飞行时间谱装置中的分光方法,以及该方法应用于小分子(如H_2S)光解动力学研究中的必要性.拉曼-α辐射(121.6 nm),用作H原子产物探测的激光,是在Kr/Ar气介质中利用四波混频产生的.利用透镜对不同波长的光有不同的折射率,四波混频后的混合光在经过一片离轴的氟化锂透镜后,121.6 nm的激光将会与212.6和84.5 nm在空间上分开.在激光到达反应中心前利用挡板挡住212.6和845 nm的激光,只让121.6 nm的光经过反应中心,从而消除212.6 nm激光产生的背景信号对实验的干扰.结合自由电子激光,成功地研究了H_2S在122.95 nm波长下的光解动力学,采集到了产物时间飞行谱.本文展示了转换得到的产物总平动能谱,解离机理与121.6 nm波长下的结果相似.实验结果显示,该方法成功地解决了分子在VUV波段进行光解动力学研究的难题,消除了这些分子在紫外光波段因为强烈吸收而产生的背景信号.     

分光技术在自由电子激光结合里德堡态氢原子飞行时间谱装置中的应用

本文描述了一种应用于自由电子激光结合高里德堡态氢原子飞行时间谱装置中的分光方法，以及该方法应用于小分子(如₂S)光解动力学研究中的必要性. 拉曼-α辐射(121.6 nm)，用作H原子产物探测的激光，是在Kr/Ar气介质中利用四波混频产生的. 利用透镜对不同波长的光有不同的折射率，四波混频后的混合光在经过一片离轴的氟化锂透镜后，121.6 nm的激光将会与212.6和845 nm在空间上分开. 在激光到达反应中心前利用挡板挡住212.6和845 nm的激光，只让121.6 nm的光经过反应中心，从而消除212.6 nm激光产生的背景信号对实验的干扰. 结合自由电子激光，成功地研究了H₂S在122.95 nm波长下的光解动力学，采集到了产物时间飞行谱. 本文展示了转换得到的产物总平动能谱，解离机理与121.6 nm波长下的结果相似. 实验结果显示，该方法成功地解决了分子在VUV波段进行光解动力学研究的难题，消除了这些分子在紫外光波段因为强烈吸收而产生的背景信号.     

丙酮/1,2-丙二醇体系的化学诱导动态电子自旋极化研究

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-.     

N2O^＋离子A^2Σ^＋电子态的光谱研究

用一束波长为360．55nm的激光，通过N2O分子的(3 1)共振增强多光子电离过程制备纯净的母体离子N2O^ X^2Π3/2,1/2(000)．用另一束可调谐激光将N2O^ 离子激发至预解离态A^2Σ^ ，利用飞行时间质谱检测解离碎片NO^ 离子强度随光解光波长的变化，在278—328nm波长范围内获得了光解碎片的激发(PHOFEX)谱．观测到了N2O^ 离子A^2Σ^ ←X^2Π电子跃迁较丰富的振动谱带．通过对PHOFEX光谱的标识，获得了A^2Σ^态较准确和全面的分子光谱常数．     

光泵香豆素染料介质光解机理的研究

本文报导C_(311)/乙醇溶液光解机理的研究.在光解前后,对香豆素C_(311)激光染料介质进行了吸收、荧光、红外和核磁共振谱的测定,实验结果表明在Nd:YAG三次谐波355nm和脉冲氙灯泵浦条件下,溶剂光解产物主要为乙酸.据此提出下列激光诱导光化学反应机理;在UV激光或脉冲氙灯泵浦条件下,溶剂中的氧由于高位三重态T_2染料分子的能量转移而被激发,并氧化香豆素分子生成隐色基.     

N2O在193nm光解：振动激发态NO（v）的生成及与N2O的碰撞驰豫

利用激光光解时间分辨富里叶红外发射谱对Ｎ２Ｏ在１９３ｎｍ光解进行了研究，观察激光光解后３０μｓ至６００μｓ次级反应产物ＮＯ（ｖ）的红外发射谱及其变化，其振动量子数ｖ高达１１，反应是通过初级光解产物Ｏ（＾１Ｄ）原子与Ｎ－Ｎ－Ｏ中末端Ｎ“头对头“碰撞进行的。利用计算机进行光谱模拟，得到ＮＯ（ｖ）各振动态的布居及随时间的演变，由此求出ＮＯ（ｖ＜１１）的各不同振动态与Ｎ２Ｏ的传能常数，对所求ｋｖ（ｖ＝１－     

NMR analysis of diacyl peroxide decomposition in methanol in response to temperature and microwave radiation

We have studied the decomposition of benzoyl and acetyl benzoyl peroxides in methanol-d₄ in response to temperature and microwave radiation. We have shown that chemically-induced dynamic nuclear polarization (CIDNP) can be observed even when the reactions are carried out in spectrometers with high magnetic fields. In this case, spin correlation persists in geminal radical pairs involving labile acyloxyl radicals. Regardless of the method used to initiate peroxide decomposition, the same amount of products are formed. Homolysis occurs according to a chain mechanism. The contribution of induced decomposition decreases over the course of the reaction. Dissolved oxygen molecules efficiently terminate the chain, decreasing the rate of peroxide decomposition. In the case of acetyl benzoyl peroxide, the product yield depends on the initiation mechanism: for microwave irradiation, the solvent molecules are more active while dissolved oxygen is less active than in thermolysis.     

Photooxidation of Histidine by 3,3′,4,4′-Benzophenone Tetracarboxylic Acid in Aqueous Solution: Time-Resolved and Field-Dependent CIDNP Study

The photooxidation reaction between 3,3′,4,4′-benzophenone tetracarboxylic acid (TCBP) and l-histidine (His) has been investigated in neutral aqueous solution using the technique of chemically induced dynamic nuclear polarization (CIDNP). Relative values of ¹³C isotropic hyperfine couplings in the TCBP and His radicals were obtained from the ¹³C-time-resolved CIDNP spectrum, recorded during the photoreaction of TCBP with His at natural abundance of the magnetic isotope ¹³C. Good agreement was found for the hyperfine coupling constants of the TCBP ketyl radical calculated using methods of density functional theory, and those obtained from the ¹³C-time-resolved CIDNP spectrum. The mechanism of the quenching reaction of triplet-excited TCBP by His in neutral aqueous solution was established. ¹H CIDNP field dependencies for the photoreaction of TCBP with His were obtained and the g-factor of the histidyl radical was found.     

吩噻嗪/二氧化钛胶体体系光诱导自由基的研究

用ESR研究了吩噻嗪(PTH)/乙二醇体系和PTH/乙二醇/TiO₂(CdS,ZnO)体系中光诱导产生的自由基PTH·⁺,发现在前者中PTH·⁺是通过光电离产生的,但在后者中PTH·⁺除通过光电离产生外,还经¹PTH^*及³PTH与TiO₂(CdS,ZnO)间的单电子转移来形成,而且PTH·⁺还与TiO₂(CdS,ZnO)发生进一步的单电子转移生成反磁性离子PTH²⁺     

Coherent Polarization Transfer Effects Are Crucial for Interpreting Low-Field CIDNP Data

In this work we demonstrate that low-field chemically induced dynamic nuclear polarization (CIDNP) is strongly affected by re-distribution of polarization, which is formed in the course of spin evolution in transient radical pairs, in diamagnetic reaction products. This phenomenon is of importance when the spins of the reaction product are coupled strongly meaning that spin–spin interactions between them are comparable to the differences in their Zeeman interactions with the external magnetic field. In this case, polarization transfer relies on a coherent mechanism; as a consequence, spins can acquire significant polarization even when they have no hyperfine coupling to the electron spins in the radical pairs, i.e., cannot be polarized directly by CIDNP. This is demonstrated by taking CIDNP of n-butylamine as an example: in this case only the α-CH₂ protons are polarized directly, which is confirmed by high-field CIDNP, whereas the β-CH₂, γ-CH₂ and δ-CH₃ protons get polarized only indirectly due to the transfer of polarization from the α-CH₂ protons. These results show that low-field CIDNP data should be interpreted with care to discriminate between the effects of spin evolution in transient radical pairs and in diamagnetic reaction products.     

A 4×4 metal-semiconductor-metal rectangular deep-ultraviolet detector array of Ga2O3 photoconductor with high photo response

A 4$\times $4 beta-phase gallium oxide ($\beta $-Ga$_{2}$O$_{3}$) deep-ultraviolet (DUV) rectangular 10-fingers interdigital metal-semiconductor-metal (MSM) photodetector array of high photo responsivity is introduced. The Ga$_{2}$O$_{3}$ thin film is prepared through the metalorganic chemical vapor deposition technique, then used to construct the photodetector array via photolithography, lift-off, and ion beam sputtering methods. The one photodetector cell shows dark current of 1.94 pA, photo-to-dark current ratio of 6$\times $10$^{7}$, photo responsivity of 634.15 A$\cdot$W$^{-1}$, specific detectivity of 5.93$\times $10$^{11}$ cm$\cdot$Hz$^{1/2}\cdot$W$^{-1}$ (Jones), external quantum efficiency of 310000%, and linear dynamic region of 108.94 dB, indicating high performances for DUV photo detection. Furthermore, the 16-cell photodetector array displays uniform performances with decent deviation of 19.6% for photo responsivity.     

CIDNP及其在光化学中的应用

化学诱导动态核极化(Chemically Induced Dynamic Nuclear Polarization,简称CIDNP)是一种在化学反应体系中观察到的NMR谱线强度反常的现象(常称之为极化谱,包括增强吸收和发射等)。1967年由Bargon和Fischer^[1] (西德)以及Ward和Lawler^[2] (美国)首先发现的。由于他们所研究的反应体系中涉及自由基,因此最初认为这种谱线强度反常现象是由于自由基中间体中的电子-核交叉弛豫引起的。这种机理通常称为:Overhauser型的动态核极化(Dynamic Nnclear Polarization简称DNP)。但很快就发现它不足以解释实验得到的结果,而CIDNP的命名却是这样因袭下来了。     

Low field CIDNP of amino acids and proteins: characterization of transient radicals and NMR sensitivity enhancement

A new method for measuring and exploiting the magnetic field dependence of chemically induced dynamic nuclear polarization (CIDNP) is described. A solution of an amino acid or protein together with a flavin photosensitizer is irradiated with laser light at a position in the bore of a superconducting NMR magnet where the field is between 0.1 T and 7.0 T. The polarized sample is then transferred by rapid injection into an NMR tube at the centre of the magnet (at 9.4 T), where the spectrum is recorded. The observed ¹H CIDNP field dependence of tyrosine agrees well with the diffusion model of the radical pair mechanism. The field dependence of histidine, tryptophan and methionine CIDNP allows the g values of the transient radicals responsible for the polarization to be determined. Experiments in which amino acids compete for the photoexcited flavin indicate that methionine residues could be used as probes of surface accessibility, especially if the polarization is generated in low fields (～ 0.7 T) and detected in high fields (≥ 9.4 T). Possible extensions of the technique to study protein folding and the structures of partially denatured states of proteins are discussed.     

光电阴极灵敏度在线检测仪的设计

介绍了利用一组干涉滤光片来实现在线检测光电阴极积分灵敏度和光谱灵敏度的一种方法。这种方法可具体描述为 :一组干涉滤光片由直流电机带动 ,按每周 40 ms的稳定转速在光路中高速旋转 ,产生的单色光按波长序列投射到光电阴极面上 ,从而产生一组光谱序列的单色光电流。这些光电流经放大、A/ D转换进入计算机 ,并经过计算在计算机屏幕上显示光电流、暗电流和光谱响应曲线。最后还讨论了排除 5 0 Hz干扰的途径和提高检测精度的方法     

The CIDNP kinetics in recombination of successive radical pairs

A theory of chemically induced dynamic nuclear polarization (CIDNP) formed in recombination of successive radical pairs (PRs) is developed. The theory is based on that of RP recombination with the spin Hamiltonian instantaneously changing in time. With kinematics approximation it is shown that general relations for CIDNP are fully expressed via the quadratures of Green functions, which characterize the molecular motion of reagents. Analytical formulae for the time dependence of CIDNP both of primary and secondary RPs have been derived in the strong magnetic field approximation (S-T₀ approximation); field dependences of stationary CIDNP effect for some model cases have been analyzed. For long-lived systems the sensitivity of secondary RP CIDNP to the singlet-triplet evolution of primary RP has been demonstrated. It is shown that sometimes the correct analysis of the effect calls for taking into account the reactivity anisotropy.