亚硝酸甲酯分子在440nm附近的激光光解

近年来亚硝酸甲酯分子（CHa0NO）的光解动力学研究十分活跃｛‘5］，主要集中在紫外激光的单光子解离的机理，光解过程的矢量相关性质和光解产物的态分布．CH30NO分子的解离能D。（CH30－NO）＝174kJ·mol‘，若单从能量上看，人＜689。的光就能使其解离，但人＞400urn的光解离研究还未见报导．＊H30＊0分子在人＞40onm的强激光场下是充电离还是先解离，是单光子解离还是多光子解离，以及通过哪个电子态解离都不清楚．时间飞行质谱不仅具有质量分辨率高、范围宽，而且响应快，因此适合做光解光电离过程初生态产物的探测．特别是时间飞…     

核黄素(维生素B2)的光物理和光化学性质

应用时间分辨的激光光解吸收技术, 详细研究了核黄素(维生素B2)的光物理和光化学性质. 在337 nm激光作用下, 可产生激发三重态(3RF*); 而在248 nm激光作用下, 既可产生激发三重态, 又可光电离生成水合电子和阳离子自由基(). 探索了激发三重态的各种反应性(能量转移、 氧化还原和抽氢反应等)及其潜在的意义, 并用自由基氧化核黄素产生阳离子自由基, 进一步验证了光解结果.     

丙酮三重态与含芳香氨基酸肽的物理化学过程

用激光闪光光解瞬态吸收光谱研究了水溶液中含芳香氨基酸残基肽的光敏化反应过程.结果表明,在丙酮存在的含色氨酸残基肽(Trp-Gly,n-f-Met-Trp,Trp-Phe)体系的光解,丙酮三重态与Trp分别通过三重态-三重态(T-T)激发能转移和电子转移生成Trp激发三重态和N中心自由基(Trp/N^·);丙酮三重态仅与含酪氨酸残基肽(Phe-Tyr)通过电子转移生成Tyr酚氧自由基(Tyr/O^·).在色氨酰酪氨酸(Trp-Tyr)与丙酮的光解体系中,观察到分子内的电子转移,即由Trp/N^·-Tyr→Trp-Tyr/O^·自由基的生成过程     

四棱草环肽C和D的ESIMS-MS分析

利用低能量碰撞诱导解离(CID)技术对四棱草环肽C和四棱草环肽D的电喷雾电离串联质谱(ESIMS-MS)进行了研究.ESIMS可以确定环肽的分子量,根据多级质谱中逐次失去氨基酸残基的碎片离子可以确定环肽中氨基酸残基的连接顺序.氨基酸残基主要从酰氨键C端断裂失去,有时亦会从N端断裂失去氨基酸残基.     

(SO4.-)诱导含硫三电子键自由基的生成机理研究

运用２４８ｎｍ激光光解瞬态吸收光谱,研究了ＳＯ４＾·－单电子氧化Ｄ－甲硫氨酸＊Ｍｅｔ）、Ｌ－甲硫氨酸甲酯（ＭＭＥ）和甲硫氨酰甲硫氨酸（Ｍｅｔ－Ｍｅｔ）的反应过程。观察到反应过程中生成３种含硫三电子键自由基中间体,［Ｓ∴Ｓ］＾＋、［Ｓ∴Ｎ］＾＋［Ｓ∴Ｏ］,并分析了反应机理。     

1,2-和1,4-萘醌248 nm激光光解的瞬态吸收光谱研究

利用纳秒级激光光解动态吸收光谱装置,研究了1,2-和1,4-萘醌中性水溶液的瞬态吸收光谱.发现1,2-萘醌及1,4-萘醌被光电离后形成的阳离子自由基在380nm均有最大吸收,但1,4-萘醌阳离子自由基在衰变过程中又形成了两种新的活性粒子,它们的最大吸收分别位于410和580nm,分析表明:410nm属于1,4-萘醌脱氢自由基的吸收,而580nm很可能归属由于电子转移而形成的瞬态产物.进一步研究发现,1,2-萘醌在中性水溶液中能被248nm激光单光子电离.     

芳香氨基酸光敏化瞬态产物的光谱学及动力学表征

运用KrF激光闪光光解瞬态吸收光谱 ,以丙酮为光敏剂 ,研究了水溶液中芳香氨基酸的光化学反应 .通过动力学分析和猝灭实验 ,鉴别了光化学反应过程中的瞬态产物 ,获取了激发三重态的瞬态吸收光谱及动力学参数 .在丙酮存在下 ,色氨酸(Trp)和酪氨酸 (Tyr)的水溶液光解 ,分别观察到Trp激发三重态、N中心色氨酸自由基 (Trp/N·)和酪氨酸的酚氧自由基 (Tyr/O·) ,阐述了二者是丙酮三重态与Trp ,Tyr分别通过三重态 三重态 (T T)激发能转移和电子转移生成 ;苯丙氨酸 (Phe)不能与丙酮三重态进行激发能转移和电子转移 .进一步 ,在色氨酰酪氨酸 (Trp Tyr)敏化光解过程中 ,观察到分子内的电子转移 ,即Trp/N· Tyr→Trp Tyr/O·自由基的生成过程 .     

用可见激光在聚(氨酯-酰亚胺)表面制备周期性亚微米结构

由于含有偶氮苯染料侧基,聚(氨酯-酰亚胺)(PUI)对532nm的光具有较强的吸收.采用该波长的可见偏振脉冲激光(Nd∶YAG激光器的倍频输出),在PUI薄膜表面制备了激光诱导周期性表面微结构(LIPSS).研究了染料引入方式以及染料侧基含量对微结构形成过程的影响,讨论了入射角、激光脉冲数、激光脉宽等激光辐射条件对LIPSS形成过程以及对微结构形貌和周期性的影响.     

氧化偶氮苯的真空紫外光电离与光离解

分子、自由基和离子的电离势及离解能等是重要的物理化学数据 .长期以来 ,这方面实验研究主要使用电子轰击电离法、或光电离方法 ,最近二十年来才逐渐出现了一些使用同步辐射光电离质谱方法进行分子、自由基光电离和光解离研究 [1－ 3].目前使用同步辐射光电离质谱法研究的对象绝大多数为结构较简单的小分子 ,最近我们使用本实验室光电离质谱及符合装置 ,对对硝基苯乙酮 [4]、对硝基苯乙醚、 对羟基偶氮苯等固体有机化合物进行了系统的研究 ,取得了一些进展 .　　偶氮染料呈现多种颜色 ,它是染料中品种最多、应用最广的一类合成染料 .偶氮染…     

含甲硫氨酸二肽的单电子氧化反应：激光闪光光解研究

运用248nm激光光解瞬态吸收光谱研究了中性水溶液中丙氨酰甲硫氨酸(Ala-Met)和N-甲酰甲硫氨酰色氨酸(N-Formyl-Met-Trp)的单电子氧化反应过程,分别观察到+和含硫三电子键的生成,但在N-甲酰甲硫氨酰色氨酸体系中没有观察到\+的生成。提出了+和含硫三电子键的生成机理,认为N-甲酰甲硫氨酰色氨酸体系不能生成+三电子键是源于其本身的分子结构。     

THE EFFECTS OF HIGH-INTENSITY UV-RADIATION ON NUCLEIC ACIDS AND THEIR COMPONENTS—I. THYMINE

Abstract— The set of final products of thymine conversion induced by high-intensity UV irradiation (λ= 266nm, intensity 10²⁴-5 × 10²⁹ photons·s⁻¹·m⁻², pulse duration 10ns) of the dilute aqueous solution to the first approximation is similar to that formed with ionizing irradiation (γ-irradiation of aqueous solution or autoradiolysis of a solid 2-[¹⁴C]-thymine). The data obtained suggest that high-intensity UV-induced photochemical conversion of thymine involves photoionization and/or photodissociation. These processes pass through the higher excited state(s) populated as a result of the second photon absorption by excited (most probably in the T₁ triplet state) thymine molecules.     

没食子酸的激光光解研究

The transient species of gallic acid(GA)have been studied by 266 nm nanosecond laser flash photolysis inaqueous solution and acetonitrile.The intermediate with absorption at 320 nm was identified as excited triplet state(~3GA~*),the decay rates of which were obtained in aqueous solution and acetonitrile respectively.Energy transferfrom ~3GA~* to β-carotene was observed and the energy transfer rate constant k_(ent)was determined to be 2.2×10~9mol~(-1)·L·s~(-1).GA underwent photoionization during photolysis and the quantum yield of photoionization was de-termined to be 0.12 at room temperature with KI as a reference.     

Photodissociation of 1-bromo-2-butene, 4-bromo-1-butene, and cyclopropylmethyl bromide at 234 nm studied using velocity map imaging

We present photofragment imaging experiments to characterize potential photolytic precursors of three C4H7 radical isomers: 1-methylallyl, cyclopropylmethyl, and 3-buten-1-yl radicals. The experiments use 2+1 resonance enhanced multiphoton ionization (REMPI) with velocity map imaging to state-selectively detect the Br(2P(3/2)) and Br(2P(1/2)) atoms as a function of their recoil velocity imparted upon photodissociation of 1-bromo-2-butene, cyclopropylmethyl bromide, and 4-bromo-1-butene at 234 nm as well as the angular distributions of the photofragments. Energy and momentum conservation allows the internal energy distribution of the nascent momentum-matched radicals to be derived. The radicals are detected with single photon photoionization at 157 nm. In the case of the 1-methylallyl radical the photoionization cross section is expected to be independent of internal energy in the range of 7-30 kcal/mol. Thus, comparison of the product recoil kinetic energy distribution derived from the measurement of the 1-methylallyl velocity distribution, detecting the radicals with 157 nm photoionization, with a linear combination of the Br atom recoil kinetic energy distributions allows us to derive reliable REMPI line strength ratios for the detection of Br atoms and to test the assumption that the photoionization cross section does not strongly depend on the internal energy of the radical. This line strength ratio is then used to determine the branching to the Br(2P(3/2)) and Br(2P(1/2)) product channels for the other two photolytic systems and to determine the internal energy distribution of their momentum-matched radicals. (We also revisit earlier work on the photodissociation of cyclobutyl bromide which detected the Br atoms and momentum-matched cyclobutyl radicals.) This allows us to test whether the 157 nm photoionization of these radicals is insensitive to internal energy for the distribution of total internal (vibrational+rotational) energy produced. We find that 157 nm photoionization of cyclopropylmethyl radicals is relatively insensitive to internal energy, while 3-buten-1-yl radicals show a photoionization cross section that is markedly dependent on internal energy with the lowest internal energy radicals not efficiently detected by photoionization at 157 nm. We present electronic structure calculations of the radicals and their cations to understand the experimental results.     

Ionic photodissociation and ionic photosensitized dissociation of charge-transfer complexes

Flash spectroscopic and kinetic studies have been carried out on the charge-transfer complex of tetracyanoethylene with tetrahydrofuran in a liquid paraffin solution at room temperature. The rise and decay curves in transient electronic absorption intensity have been observed with a common rate constant, corresponding to the anion radical of tetracyanoethylene and the triplet state of the charge-transfer complex, respectively. From the kinetic analysis it has been concluded that the ionic photodissociation of this complex takes place in its lowest excited triplet state. This dissociation mechanism has also been confirmed by employing a triplet energy transfer technique with which “ionic photosensitized-dissociation” phenomenon is observed. Furthermore, a few other examples of ionic photosensitized-dissociation are demonstrated in rigid glasses with typical weak charge-transfer complexes whose photodissociation processes are well-known.     

一氯甲烷同步辐射光电离研究: 离子生成焓与键能的测定

本文报道超音速射流冷却条件下, 用同步辐射光研究CH3Cl光电离及其解离电离的动力学, 测得CH3Cl的电离能(IP)为11.28±0.01eV。通过测定CH3Cl光解离电离碎片的出现势(AP), 并结合有关已确认的热力学数据, 获得了它们的标准生成焓、离子型分子中的键能、中性分子或自由基中的键能及母体离子的解离能等热力学数据。对CH3Cl分子VUV光解离电离通道进行了分析。     

Primary photophysical properties of ofloxacin

Steady-state fluorescence has been used to study the excited singlet state of ofloxacin (OFLX) in aqueous solutions. Fluorescence emission was found to be pH dependent, with a maximum quantum yield of 0.17 at pH 7. Two pKa*s of around 2 and 8.5 were obtained for the excited singlet state. Laser flash photolysis and pulse radiolysis have been used to study the excited states and free radicals of OFLX in aqueous solutions. OFLX undergoes monophotonic photoionization from the excited singlet state with a quantum yield of 0.2. The cation radical so produced absorbs maximally at 770 nm with an extinction coefficient of 5000 +/- 500 dm3 mol-1 cm-1. This is confirmed by one-electron oxidation in the pulse radiolysis experiments. The hydrated electron produced in the photoionization process reacts with ground state OFLX with a rate constant of 2.0 +/- 0.2 x 10(10) dm3 mol-1 s-1, and the anion thus produced has two absorption bands at 410 nm (extinction coefficient = 3000 +/- 300 dm3 mol-1 cm-1) and at 530 nm. Triplet-triplet absorption has a maximum at 610 nm with an extinction coefficient of 11,000 +/- 1500 dm3 mol-1 cm-1. The quantum yield of triplet formation has been determined to be 0.33 +/- 0.05. In the presence of oxygen, the triplet reacts to form both excited singlet oxygen and superoxide anion with quantum yields of 0.13 and < or = 0.2, respectively. Moreover, superoxide anion is also formed by the reaction of oxygen with the hydrated electron from photoionization. Hence the photosensitivity due to OFLX could be initiated by the oxygen radicals and/or by OFLX radicals acting as haptens.     

UV photodissociation of the van der Waals dimer (CH3I)2 revisited: pathways giving rise to ionic features

The CH(3)I A-state-assisted photofragmentation of the (CH(3)I)(2) van der Waals dimer at 248 nm and nearby wavelengths has been revisited experimentally using the time-of-flight mass spectrometry with supersonic and effusive molecular beams and the "velocity map imaging" technique. The processes underlying the appearance of two main (CH(3)I)(2) cluster-specific features in the mass spectra, namely, I(2)(+) and translationally "hot" I(+) ions, have been studied. Translationally hot I(+) ions with an average kinetic energy of 0.94+/-0.02 eV appear in the one-quantum photodissociation of vibrationally excited I(2)(+)((2)Pi(32,g)) ions (E(vib)=0.45+/-0.11 eV) via a "parallel" photodissociation process with an anisotropy parameter beta=1.55+/-0.03. Comparison of the images of I(+) arising from the photoexcitation of CH(3)I clusters versus those from neutral I(2) shows that "concerted" photodissociation of the ionized (CH(3)I)(2)(+) dimer appears to be the most likely mechanism for the formation of molecular iodine ion I(2)(+), instead of photoionization of neutral molecular iodine.     

Laser two-photon ionization spectroscopy of molecules in liquids

A two-photon lonization technique has been developed and applied to determine the photoionization threshold of a molecule in liquid solution. The photoionization of pyrene in n-pentane was studied by monitoring the photocurrent of an≈ 10^?6 M solution as a function of the laser wavelength in the region 360–530 nm, corresponding to two-photon, transition in the region 180–265 nm. The photoionization threshold thus determined is 4.80 ± 0.02 eV. Resonances were observed in the two-photon ionization spectrum which are tentatively ascribed to preionization of one-photon forbidden transitions to states energetically degenerate with the continuum, reached via two-photon absorption.     

Branching ratio for S(33Pj) AND S(31D2) atom production in the photodissociation of CS2 at 193 nm

Resonance-enhanced photoionization has been used to follow S(³P₂) in the photodissociation of CS₂ at 193 nm. The contributions from initial photodissociation and from S(¹D) relaxation have been resolved and give a (15±5)% yield of S(¹D). The possibility of secondary production of S(³P_j) by CS photodissociation with a second 193 nm photon is discussed. Although this might raise the S(¹D) yield to (26±8)%, production of S(³P_J) is still the dominant photodissociation channel.     

EXCITED STATES IN PHOTODIMERIZATION OF AQUEOUS TYROSINE AT ROOM TEMPERATURE

Abstract— The photoionization of tyrosine in aqueous solution in the liquid state was studied at room temperature by analyzing the kinetics of formation of bityrosine upon irradiation of tyrosine, and the external heavy-atom effect on the formation of bityrosine. The relative number of bityrosine molecules was determined by measuring the fluorescence intensity at 400 nm. A kinetic model for the formation of bityrosine was formulated on the assumption that the rate constants were first-order for production of radicals and for recombination with ejected electrons. The applicability of this model to the present case was confirmed by the experimental data. On the basis of the model, we found that the electronic process of photoionization of tyrosine at room temperature is different in acidic and alkaline media. In acidic media a tyrosine molecule absorbs one light quantum and photoionizes through a singlet excited state, while in alkaline media a tyrosinate ion photoionizes after absorption of two light quanta. The intermediate product that absorbs the second photon is in a triplet excited state.