Laser-induced fluorescence study of the hydrogen atom formation dynamics in the 248 nm gas-phase photodissociation of vibrational state selected water (H<Subscript>2</Subscript>O (|04<Superscript>−</Superscript>〉))

The vibrationally-mediated H₂O gas-phase photodissociation was studied at a photolysis wavelength of 248 nm. Single rotational states of the |03⁻〉|2〉 and |04⁻〉 H₂O overtone vibrations were prepared by laser photoexcitation around 720 nm. H atoms formed in the photodissociation of the H₂O (|04⁻〉 = 3₁₃) were detected by Lyman-α laser-induced fluorescence spectroscopy with sub-Doppler resolution to determine their translational energy. The present result confirms that in the dissociation process the major part (ca. 93%) of the available energy is released as relative translational energy of the nascent H + OH photofragments, in agreement with earlier complementary measurements (R. L. Vander Wal, J. L. Scott and F. F. Crim, J. Chem. Phys. 94, 1859 (1991)), where the internal excitation of the OH product radical was investigated at different photolysis wavelengths.     

Photoregulation of protein plasmid expression in vitro and in vivo using BHQ caging group

Green fluorescent protein(GFP) plasmid was caged by 8-bromo-7-hydroxyquinolinyl chromophore(BHQ) for controlling its expression with exact spatiotemporal resolution.In vitro and in vivo experiments clearly verified that,comparing with Bhc caging, the expression level of caged GFP plasmid was dramatically decreased and then efficiently restored after subsequent photolysis.     

Ultraviolet photolysis assisted mineralization and determination of trace levels of Cr, Cd, Cu, Sn, and Pb in isosulfan blue by ICP-MS

Isosulfan blue dye is used in sentinel node mapping technique to evaluate breast cancer patients where determination of different trace elements is required. A UV-photolysis assisted mineralization of isosulfan blue is described here for the determination of trace elements (Cr, Cd, Cu, Sn and Pb) by Inductively Coupled Plasma Mass Spectrometry (ICP-MS). In the present study advanced oxidation processes such as UV, UV/H₂O₂, and UV/H₂O₂/HNO₃ have been assessed and compared for the degradation and mineralization of isosulfan blue dye. The extent of mineralization was determined on the basis of total organic carbon (TOC) measurement. The adopted procedure (UV/HNO₃/H₂O₂) provided very low TOC content (0.5%), corresponding to a mineralization efficiency of > 99%. With the present procedure, the use of dynamic reaction cell (DRC) or collision cell was not required for chromium determination which suffers interference from the presence of carbon. Method detection limits were 0.0028, 0.0021, 0.016, 0.007, and 0.005 μg g^? 1 for Cr, Cd, Cu, Sn and Pb respectively. The values obtained by the proposed method were cross-validated by those obtained by ETAAS analysis. The expanded uncertainties in the measurement at 95% confidence level (coverage factor 2) are in the range of 13.7–25.8%.     

Photoproduction and determination of hydroxyl radicals in aqueous solutions of Fe(III)–tartrate complexes: a quantitative assessment

Benzene has been used as a probe to determine the photogeneration of ^·OH radicals in aqueous solutions containing Fe(III) and tartrate (Tar) when they are irradiated (λ?≥?313?nm, 250?W). Products were determined by HPLC. Results show that tartrate has a positive effect on the photogeneration of ^·OH. The influence of pH, temperature, and concentrations of Fe(III) and Tar were systematically investigated. Production of ^·OH radicals was greatest at pH 3.0. Concentrations of ^·OH increased with increasing Fe(III) and tartrate concentrations, but at a certain ratio they decreased. The quantum yield of ^·OH radicals at 328?K was nearly twice that at 298?K.     

H-Ge bond activation by tungsten carbonyls: An experimental and theoretical study

The activation of the Ge-H bond and the formation of several hydride complexes, characterized by high-field resonances, have been detected during the ¹H NMR spectroscopy monitoring of the photochemical reaction of Et₃GeH and Et₂GeH₂ with W(CO)₆ and the norbornadiene complex [W(CO)₄(η⁴-nbd)]. The activation of the Ge-H bond of triethylgermane in the photochemical reactions of tungsten(0) complexes has been applied in the hydrogermylation of norbornadiene (nbd), which leads to the formation of endo-triethylgermylnorbornene as the major product. The complex [{W(μ-η²-H-GeEt₂)(CO)₄}₂] has been fully characterized by NMR spectroscopy and by a single-crystal X-ray diffraction study. Evidence for the hydride ligand of the W(μ-η²-H-GeEt₂) group has been provided by ¹H NMR spectroscopy (δ = −9.02, ¹J_H-W = 31 Hz) and by DFT calculations. A DFT study of the structural properties and ¹H NMR chemical shifts of several possible intermediate σ and hydride complexes formed during the photochemical reaction of W(CO)₆ and Et₂GeH₂ has been performed.     

Low temperature SPME device: A convenient and effective tool for investigating photodegradation of volatile analytes

Hexachlorobenzene (HCB), a model volatile compound, was exposed to UV irradiation (16 W, 254 nm) after being sorbed in an internally cooled or low temperature solid-phase microextraction (LT-SPME) fibre. Photolysis took place directly on the polydimethylsiloxane coating of the LT-SPME fibre, yielding an “in situ” generation of photoproducts. Maintaining the temperature of the cold fibre at 0 °C eliminated, for the first time, problems of analyte losses due to volatilisation, inherent to the conventional room temperature photo-SPME studies. During the present studies, nearly complete photoremoval of HCB could be achieved within 20 min of irradiation. Photoreduction through photodechlorination was shown to be the main decay pathway in which lesser chlorinated congeners were sequentially formed as intermediates. Accordingly, initial generation of pentachlorobenzene was followed in order from 1,2,3,5-tetrachlorobenzene, 1,2,4,5-tetrachlorobenzene and 1,3,5-trichlorobenzene. The present findings were in agreement with previously reported results. Overall, the use of the LT-SPME device as a photoreaction support not only eliminated analyte losses but also greatly facilitated photochemical investigations of volatile compounds in general.     

Nanosecond probing of the early nucleation steps of silver atoms in colloidal zeolite by pulse radiolysis and flash photolysis techniques

The process of formation and the subsequent aggregation of silver atoms (Ag⁰) in nanosized zeolite beta (BEA) are studied by transient absorption spectroscopy. The zeolite nanocrystals are stabilized in aqueous colloidal suspensions with a narrow particle size distribution in the range 30–60 nm. The reduction of silver cations is initiated either by pulse radiolysis of the aqueous suspension or by photoinduced electron transfer using an organic electron donor adsorbed in the zeolite framework. The silver atom in BEA nanosized crystals is found to be stable on the microsecond timescale.     

Ag/Ag2WO4等离子体共振催化剂可见光催化还原CO2

转化CO₂为有机组分是缓解全球变暖和保障持续能源供给的有效方法之一.采用简易的离子交换结合水合肼还原法制备了一系列不同晶相Ag₂WO₄载银(Ag/Ag₂WO₄)的等离子共振光催化剂,并用X射线衍射(XRD)、X射线光电子能谱(XPS)、扫描电子显微镜-能量色散X射线光谱(SEM-EDS)、紫外-可见(UV-Vis)吸收光谱和比表面积测试对催化剂进行了表征.较之Ag₂WO₄, Ag/Ag₂WO₄在可见光催化还原CO₂生成CH₄时显示了明显提高的量子产率(QY)、能量投入产出比(EROEI)、转换数(TON),就Ag/α-Ag₂WO₄, Ag/β-Ag₂WO₄和Ag/γ-Ag₂WO₄而言,最佳催化剂为Ag/β-Ag₂WO₄,其实际最佳Ag:Ag₂WO₄摩尔比为4:96,该催化剂还原CO₂为CH₄的QY、EROEI、TON和拟一级反应速率常数分别为0.145%、0.067%、9.61和1.96×10^-6 min^-1.此外,制备的等离子共振Ag/Ag₂WO₄光催化剂在可见光辐照下进行循环反应仍能保持稳定性.局域表面等离子共振效应是强化Ag/Ag₂WO₄光催化剂活性和稳定性的主要原因.     

铁－芳烃络合物光引发剂的吸收光谱研究

铁－芳烃络合物光引发剂的吸收光谱研究陈旭东，黄新华陈用烈，梁兆熙（西南师范大学化学系重庆，６３０７１５）（中山大学高分子研究所广州）关键词铁－芳烃络合物，光引发剂，吸收光谱，光解铁－芳烃络合物作为环氧化物阳离子聚合光引发剂已引起人们关注［１，２］．我...     

二氧化三氮(N3O2)中性分子和离子的一些重要反应过程的理论研究

二重态的N3O2中性分子作为中间体, 在N3O2阴离子的光解离反应和NO+N2O←→N2+NO2反应中均起重要作用. 在CCSD(T)/6-311G(d,p)//B3LYP/6-311G(d,p)+ZPE的水平上, 对这两个反应进行了理论计算. 结果表明, 在N3O2阴离子的光解离反应中, 该阴离子先在光照下解离为与其具有相同的W构型的中性分子和一个电子, 这个中性分子是一个过渡态, 它将打破C2v构型变成具有Cs对称性的W型中间异构体, 然后再经过一个过渡态, 裂解成N2O+NO两个小分子. 这个裂解过程的能垒非常低(5.96 kJ/mol), 因此在实验中很难检测到W型的中间异构体. 在另一个重要的[N3O2]体系的反应(NO+N2O←→N2+NO2)中, 找到了两条反应通道, 其中不经过中间异构体的一步转化通道更为可行.