氯甲烷分子在13至17 eV激发能量范围内的电离解离

利用阈值光电子-光离子符合飞行时间质谱研究了氯甲烷分子在13至17eV激发能量范围内的光电离和光解离动力学.在此能量范围内,电离产生的CH3Cl+离子处于A2A1和B2E电子激发态.两电子态均为完全解离态,可生成CH3+和CH2Cl+碎片离子,其中CH3+是最主要的解离产物.拟合CH3+离子的符合飞行时间质谱峰形,可以得到CH3Cl+离子解离过程中释放的平动能分布,结果显示CH3Cl+离子A2A1态解离生成CH+3的过程接近直接解离机理,而B2E态的解离过程则具有统计解离的特征.此外,结合理论计算的势能面信息,我们推测在A2A1态出现的CH2Cl+碎片离子来源于CH3Cl分子自电离产生高振动激发的CH3Cl+(X2E)离子统计解离过程.     

呋喃分子多光子电离解离过程的反应通道

1引言呋喃分子在450nm附近的多光子电离实验中[1]，质谱中观察不到母体离子C4H4O＋，主要碎片离子的相对丰度C＋＞C2＋＝CHO＋＝C3H3＋．这些离子的选质量光谱研究表明它们是呋喃分子先吸收3＋1个光子电离为母体离子C4H4O＋，然后C4H4O＋再进一步吸收光子逐步解离产生．陕哺离子的初级解离过程已比较清楚[2－4]，吹响离子能量在1～5eV之间解离通道是：这三个平行解离反应可用RRKM理论来描述[4]．但是陕哺离子在高能量下的解离反应，特别是次级解离过程还不清楚，因此无法确定MPIF实验中观察到小离子碎片产生的机理，为此本文在速…     

环氧乙烷的真空紫外同步辐射光电离与光解离

利用真空紫外同步辐射和自制的飞行时间质谱（TOF－MS）仪,研究了环氧乙烷的光电离与光解离过程,通过测量各离子的光电高效率（PIE）曲线,获得了该分子的电离势和所有碎片离子的出现势．分析了离子的光电离解离通道,并讨论了它们的竞争情况．结合有关公认的热力学数据,算出它们的标准生成焓．     

二乙基锌的同步辐射真空紫外光电离光解离

利用同步辐射光源和反射式飞行时间质谱, 在超声冷却条件下对二乙基锌(ZnC4H10)进行真空紫外(VUV, 能量范围为8-22 eV)光电离光解离研究. 实验获得ZnC4H10的光电离质谱图; 通过测量各碎片离子的光电离效率(PIE)曲线, 获得ZnC4H10的电离势(IP=8.20±0.05 eV)及其碎片离子(ZnC2H5+、ZnH+、Zn+、C2H5+、C2H3+等)的出现势. 根据实验结果, 并结合相关文献所给的热力学数据, 推导出这些主要碎片离子的生成焓, 并分析它们可能的解离通道和主要离子的分支比. 结果表明, 其主要解离通道是母体离子发生Zn—C 键的断裂形成ZnC2H5+和C2H5+离子, ZnC2H5+离子再进一步解离形成Zn+离子, 并且含锌碎片离子的丰度占75%以上.     

243～263nm CH3COCH3 的多光子电离研究

在243～263 nm紫外光波段通过质量选择光电离激发谱研究了丙酮（CH3COCH3）的光化学反应通道。分析母体离子CH3COCH3+和碎片离子CH3CO+ 、 CH3+的光电离激发谱和质谱峰宽可以知道: 此光波段丙酮分子的光化学反应主要包括了丙酮分子经由(S1,T1)中间态产生母体离子的（1+1）双光子电离通道,母体离子进一步解离产生碎片离子CH3+的“光电离-光解离”通道和丙酮分子经由(S1,T1)中间态解离成中性自由基碎片CH3CO后再进一步被双光子电离的“光解离-光电离”通道。由母体离子光电离激发谱双光子阈值波长（255.67 nm）给出的丙酮电离势（IP）为（9.696±0.004）eV。     

二溴甲烷的同步辐射光电离研究

采用５０～２００ｎｍ同步辐射光，对ＣＨ２Ｂｒ２的光电离过程进行了研究，根据测定的母体离子及其碎片离子出现势，得到二溴甲烷的绝热电离势为１０．２３±０．０１ｅＶ，并获得了离子的生成焓，解离能及键能等热力学数据，分析了碎片离子的光解离电离通道。     

1-丙醇和2-丙醇的真空紫外光电离质谱研究

研究了在9.84 – 11.80 eV光子能量范围内1-丙醇和2-丙醇的光电离和离解光电离，测量了1-丙醇离解电离产生的碎片离子CH3CH2CH2OH+, CH3CH2CHOH+, CH2CH2OH+, CH3CH2CH2+, CH3CH=CH2+和CH2OH+及2-丙醇离解电离产生的碎片离子CH3CH(OH)CH3+, CH3C(OH)CH3+, CH3CHOH+, CH2=CHOH+, CH3CHCH3+和CH3CH=CH2+的光电离效率谱，得到了这些离子的出现势。结合从头算理论计算，给出了1-丙醇的碎片离子CH3CH2CHOH+, CH2CH2OH+, CH3CH2CH2+, CH3CH=CH2+, CH2OH+和2-丙醇的碎片离子CH3C(OH)CH3+, CH3CHOH+, CH2=CHOH+, CH3CHCH3+, CH3CH=CH2+等的解离通道和解离能。理论计算结果与实验结果符合得很好。     

氟里昂134a的真空紫外光电离和光解离的同步辐射研究

利用同步辐射真空紫外光研究了氟里昂134a(CH₂FCF₃)的光电离和光解离过程,通过测量各离子的光电离效率曲线,得到了该分子的电离能(12.68±0.04)eV和所有碎片离子的出现势,运用Gaussian-03计算了母体和中性碎片及相应离子的电子态、对称性和能量.结合理论计算结果对离子出现势的理论值和实验值进行了比较,分析了母体离子可能的光解离通道.     

丙烯酸分子的激发态超快预解离动力学

利用飞秒泵浦-探测技术结合飞行时间质谱(TOF-MS),研究了丙烯酸分子被200nm泵浦光激发到第二电子激发态(S2)后的超快预解离动力学.采集了母体离子和碎片离子的时间分辨质谱信号,并利用动力学方程对时间分辨离子质谱信号进行拟合和分析,揭示了预解离通道的存在.布居在S2激发态的分子通过快速的内转换弛豫到第一电子激发态(S1),时间常数为210fs,随后再经内转换从S1态弛豫到基态(S0)的高振动态,时间常数为1.49ps.分子最终在基态高振动态势能面上发生C-C键和C-O键的断裂,分别解离生成H2C=CH和HOCO、H2C=CHCO和OH中性碎片,对应的预解离时间常数分别约为4和3ps.碎片离子的产生有两个途径,分别来自于母体离子的解离和基态高振动态势能面上中性碎片的电离.     

碘代烷烃在532 nm激光作用下多光子电离解离机理

利用５３２ｎｍ的激光对碘代烷烃（碘甲烷、碘乙烷、碘代正丙异丙烷）分子作了多光了电离解离（ＭＰＩＤ）质谱（ＭＳ）研究,在５３２ｎｍ激光作用下,ＣＨ３Ｉ分子吸收５３２ｎｍ激光双光子的能量,进入Ａ带的ＩＡ２态,继续吸收光子上泵浦至电离态形成母体离子ＣＨ３Ｉ,然后再形成碎片离子;而其它几个碘代烷烃吸收双光子的能量进入Ａ带后均形成中性碎片,中性碎片再吸收光子经一系列电离解离形成碎片离子,此外,本文还通过对同     

Hydrogen bonds in 1,4-dioxane/ammonia binary clusters

With synchrotron radiation, we have studied the photoionization and dissociation of 1,4-dioxane/ammonia clusters in a supersonic expansion. The observed major product ions are the 1,4-dioxane cation M(+) and protonated cluster ions M(NH(3))(n)H(+) (where M=1,4-dioxane), and the intensities of the unprotonated cluster ions M(NH(3))(n) (+) are much lower. Fully optimized geometries and energies of the neutral cluster M(NH(3))(2) and related cluster ions have been obtained using the ab initio molecular orbital method and density functional theory. The potential energy surface of the excited state of M(NH(3))(2) (+) was also calculated. With these results, the mechanisms of different photoionization-dissociation channels have been suggested. The most probable channel is electron ejection from the highest occupied molecular orbital, followed by the dissociation into M(+) and (NH(3))(2). For another main channel, after removing an electron from the second highest occupied molecular orbital, the intracluster proton transfer process takes place to form the stable unprotonated cluster ion M(NH(3))H(+)-NH(2), which usually leads to the dissociated protonated cluster ion M(NH(3))H(+) and a radical NH(2).     

Spectroscopic studies of zinc(II)tetraphenylporphyrin molecular complex with 1,4-dioxane

The molecular complex of zinc(II)tetraphenylporphyrin with 1,4-dioxane has been obtained. The IR spectra of the [Zn(TPhP)(1,4-dioxane)2] stabile molecular complex between 4000 and 50cm(-1) have been studied. An interpretation is given on the base the "chair" conformation of 1,4-dioxane molecule.     

Synthesis and some chemical conversions of acetylenic derivatives of 1,4-dioxane

The possibility has been shown of synthesizing acetylenic derivatives of 1,4-dioxane in high yield by the interaction of glycidyl ethers of acetylenic alcohols with ethylene bromohydrin in the presence of boron trifluoride etherate. Dehydrobromination of the corresponding bromohydrin was then carried out in the presence of metallic sodium in absolute diethyl ether. Acetylenic derivatives of 1,4-dioxane enter into hydrosilylation, aminomethylation, and diene condensation reactions with the formation of new derivatives of 1,4-dioxane.     

Photoabbau von Polymethylmethacrylat in Lösung

Zusammenfassung Der photochemische Abbau von Polymethylmethacrylat in Chloroform und in 1,4-Dioxan wurde in Anwesenheit von Maleinsäureanhydrid in Luftgegenwart untersucht. Maleinsäureanhydrid verzögert den Photoabbau des Polymeren in 1,4-Dioxan viel wirkungsvoller als in Chloroform. 1,4-Dioxan bildet mit Maleinsäureanhydrid einen Elektronen-Donator-Acceptor-Komplex, der für die Verzögerung des Abbaues verantwortlich ist.

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Summary The photodegradation of polymethylmethacrylate in chloroform and in 1,4-dioxane has been investigated in air in the presence of maleic anhydride. Maleic anhydride retards the photodegradation more effectively in 1.4-dioxane than in chloroform. The retardation of the degradation in 1.4-dioxane has been then interpreted as a direct sequence of the charge-transfer formation between the solvent and maleic anhydride.

     

Free-radical chain oxidation of 1,4-dioxane inhibited by 2-thio-6-aminouracil

The effect of 2-thio-6-aminouracil on the oxygen uptake kinetics has been studied in 1,4-dioxane free-radical chain oxidation as a model system. The presence of a thiocarbonyl group in the 2-position of the uracil ring makes 6-aminouracil highly reactive towards 1,4-dioxane peroxy radicals. The rate constant of the 1,4-dioxane peroxy radical interaction with 2-thio-6-aminouracil has been measured to be k₇ = (3.0 ± 0.5) × 10⁵ L mol^–1 s^–1 (333 K). The stoichiometric inhibition factor f = 1.1 ± 0.1 has been determined.     

Molar excess volumes of 1,4-dioxane+ acetonitrile,n-butylamine+acetonitrile andn-butylamine+1,4-dioxane at different temperatures

Molar excess volumes and partial molar volumes are reported for binary mixtures of 1,4-dioxane + acetonitrile, n-butylamine + acetonitrile and n-butylamine + 1,4-dioxane at five different temperatures and over the complete concentration range. The Prigogine-Flory-Patterson model of solution thermodynamics has been used to predict the excess molar volumes. This work shows the importance of the three contributions: interactional, internal pressure and free volume, to the excess volume.     

Synthesis and properties of diphenoxo-bridged CoII, NiII, CuII, and ZnII complexes of a new tripodal ligand: generation and properties of MII-coordinated phenoxyl radical species

Four dinuclear complexes of composition [MII2(L)2].xS [M=Co, x=0.5, S=1,4-dioxane (1.0.5 1,4-dioxane); Ni, x=0 (2) [single crystals have x=2, S=diethyl ether (2.2 diethyl ether)]; Cu, x=0 (3); Zn, x=0.5, S=1,4-dioxane (4.0.5 1,4-dioxane)] have been synthesized using a new tripodal ligand [2,4-di tert-butyl-6-{[(2-pyridyl)ethyl](2-hydroxybenzyl)-aminomethyl}-phenol (H2L)], in its deprotonated form, providing a N 2O 2 donor set. Crystallographic analyses reveal that the complexes have a similar diphenoxo-bridged structure. Each metal ion is terminally coordinated by 2,4-di tert-butyl-phenolate oxygen, a tertiary amine, and a pyridyl nitrogen. From each ligand, unsubstituted phenolate oxygen provides bridging coordination. Thus, each metal center assumes M (II)N 2O 3 coordination. Whereas the geometry around the metal ion in 1.0.5 1,4-dioxane, 2.2 diethyl ether and, 4.0.5 1,4-dioxane is distorted trigonal-bipyramidal, in 3 each copper(II) center is in a square-pyramidal environment. Temperature-dependent magnetic behavior has been investigated to reveal intramolecular antiferromagnetic exchange coupling for these compounds (-J=6.1, 28.6, and 359 cm(-1) for 1.0.5 1,4-dioxane, 2, and 3, respectively). Spectroscopic properties of the complexes have also been investigated. When examined by cyclic voltammetry (CV), all four complexes undergo in CH2Cl2 two reversible ligand-based (2,4-di tert-butylphenolate unit) one-electron oxidations [E1/2(1)=0.50-0.58 and E1/2(2)=0.63-0.75 V vs SCE (saturated calomel electrode)]. The chemically/coulometrically generated two-electron oxidized form of 3 rearranges to a monomeric species with instantaneous abstraction of the hydrogen atom, and for 4.0.5 1,4-dioxane the dimeric unit remains intact, exhibiting an EPR spectrum characteristic of the presence of ZnII-coordinated phenoxyl radical (UV-vis and EPR spectroscopy). To suggest the site of oxidation (metal or ligand-centered), in each case DFT calculations have been performed at the B3LYP level of theory.     

Occurrence of 1,4-dioxane in cosmetic raw materials and finished cosmetic products.

Surveys of cosmetic raw materials and finished products for the presence of the carcinogen 1,4-dioxane have been conducted by the U.S. Food and Drug Administration since 1979. Analytical methods are described for the determination of 1,4-dioxane in ethoxylated cosmetic raw materials and cosmetic finished products. 1,4-Dioxane was isolated by azeotropic atmospheric distillation and determined by gas chromatography using n-butanol as an internal standard. A solid-phase extraction procedure based on a previously published method for the determination of 1,4-dioxane in cosmetic finished products was also used. 1,4-Dioxane was found in ethoxylated raw materials at levels up to 1410 ppm, and at levels up to 279 ppm in cosmetic finished products. Levels of 1,4-dioxane in excess of 85 ppm in children's shampoos indicate that continued monitoring of raw materials and finished products is warranted.     

Conformational analysis of trans-2,3-diaryloxy-1,4-dioxanes. A tool for discriminating between steric and electronic effects in the position of

The conformation of several $\text{trans}$-2,3-diaryloxy-1,4-dioxanes has been studied using ¹H NMR techniques. $\text{Trans}$-2,3-bis(4-nitrophenoxy)-1,4-dioxane and $\text{trans}$-2,3-bis(4-methoxyphenoxy)-1,4-dioxane have been found to be predominantly ( ≈98%) in diaxial conformation in CDCl₃). On the other hand, $\text{trans}$-2,3-bis(2,6-dimethylphenoxy)-1,4-dioxane exists in the same conditions as a 66:33 mixture of diaxial and diequatorial conformers. An explanation based on the fulfilment of the exo-anomeric effect is provided.     

Analysis of Oxygenated Solvents in Groundwater by Dynamic Thermal Stripping-GC-MSD

Abstract

Analysis of three oxygenated solvents (acetone, THF and 1,4-dioxane) in groundwater was conducted by dynamic thermal stripping followed by thermal desorption into a GC-MSD with monitoring of selected ions. This method has a significantly better practical quantitation limit than the current EPA method (13 vs. 150 μg/L for 1,4-dioxane). Using this method a plume of groundwater contaminated with 1,4-dioxane emanating from a former solvent disposal site was mapped. More than 10 years after disposal, concentrations of 1,4-dioxane greater than 3 mg/L were measured at points more than 300 m from the site.