丁酮分子的共振增强多光子电离解离研究

利用可调谐染料激光研究了丁酮分子的共振增强多光子电离解离过程,发现在428～448nm激光波段丁酮分子发生的是经4p和4dRydberg态的(3+1)多光子过程。此外,我们还用“梯开关”模型对丁酮母体离子的解离机理和各碎片来源作了详细的分析,分析认为在丁酮母体离子的解离过程中存在H原子重排与电荷的重新分布现象。     

甲胺分子多光子电离质谱研究

胜多光子电离飞行时间质谱法，利用可调谐脉冲激光器，测得了甲胺分子在不同激光波长和激光功率下的多光子电离和解离产物。母体离子ＣＨ３ＮＨ＾＋２的离解速常数随激光发波长的增大而减小。     

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…     

多光子电离伴随的碎片化过程的速率方程分析

提出一个描述多原子分子多光子激发、电离和离子再被激发过程的布局速率方程模型，并且得到电离效率和离子体系吸收的平均能量＜E＞的代数解．通过计算这两个量与光强的关系，分析了不同电离机制下，多原子分子多光子电离实验中伴随的碎片化过程的控制性问题．结果表明只有采用1＋1电离方案，可以通过控制电离激光的强度来实现“软电离”和“硬解离”．采用3＋1电离，即使在单离子条件下，离子的＜E＞已高达20－30eV，远超过离子的解离阈值，特别是增加光强时，＜E＞的增加速度比电离效率增加得快，因此一般条件下不能让分子有效电离而不使其离子解离．上面的分析可以圆满解释呋喃等分子在3＋1电离时观察不到母体离子这个实验事实．     

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     

溴代烷烃在紫外波段的光解离过程

在飞行时间质谱仪中，采用波长为234 nm和267 nm的激光，研究溴代烷烃CHBr3、CH2Br2、C2H5Br及C2H4Br2的光离解过程.在UV激光的作用下，溴代烷烃分子主要发生的是吸收1个光子解离出Br原子，然后继续吸收光子发生Br原子的（2＋1）共振增强多光子电离的过程.其中由溴代烷烃分子解离得到的Br原子可能存在着两种布居：基态Br(2P03/2)及激发态Br*(2P01/2).研究解离得到的Br原子的分支比 N(Br*)/N(Br)，并给出测量结果：溴代烷烃分子解离得到的Br原子在267 nm激光作用下的分支比明显大于在234 nm激光作用下的结果.对此多光子过程的机理，也进行了分析讨论.     

溴甲烷在强激光场中的电离和解离

利用自制的反射式飞行时间质谱仪(RTOF-MS)研究了多原子分子CH₃Br在强激光场中的电离解离. 得到了溴甲烷在强激光场中电离解离的飞行时间质谱, 基于RTOF-MS的高分辨率(M/ΔM>2000), 测量了分子库仑爆炸产生的系列碎片离子的动能释放(KER), 用多光子解离和库仑爆炸解释了实验结果. 与碘甲烷在强场中的实验结果对比发现: (1) 在相同的激光场强下, 碘甲烷电离解离的最高价碎片离子为I⁶⁺而溴甲烷为Br³⁺; (2) 溴甲烷质谱中存在母体离子的脱氢产物CH_mBr⁺ 和CH_mBr²⁺, 而对于碘甲烷, 没有检测到这些通道, C-I键首先断开; (3) 质谱中存在H⁷⁹Br⁺和H⁸¹Br⁺, 而碘甲烷的电离解离中不存在HI产物; (4) 溴甲烷库仑两体爆炸的有效电荷间距随着两碎片电荷乘积的增大而增大, 而对于碘甲烷此间距几乎不随电荷乘积变化; (5) CH_m⁺(m=0, 1, 2)的主要生成通道可能与碘甲烷不同, 不是来自CH₃⁺的顺序脱氢, 而是来自脱氢母体离子的直接解离.     

二乙胺分子的多光子电离：“梯转换”过程

二乙肤的红外光谱[1]和泛频吸收谱[2]有一定研究，其电子轰击电离[3，4]、场致电离[5]和电子轰击所产生离子的红外多光子及碰撞解离[6]表明，母体离子的碎裂以α键的断裂，从而失去甲基并形成亚胺离子为主．二乙胺分子中N原子与其他原子的构型成锥形，而在母体离子中则成平面结     

飞秒脉冲作用下氯丙烯的多光子解离和电离动力学（英文）

利用飞秒激光脉冲,在200、400和800 nm下对氯丙烯(C_3H_5Cl)的光解离和电离动力学进行了研究。实验测量了氯丙烯在飞秒脉冲作用下的飞行时间质谱、光强指数以及光电子影像。结果发现在短波(200 nm)时,母体分子的电离为主要通道,而其他离子均来源于C_3H_5Cl~+的解离。当波长移动到长波(800 nm)时,碎片离子就占据了主导。这些碎片离子来源于中性碎片的多光子电离过程,而这些中性碎片又是由C_3H_5Cl的中间态直接解离而产生的。这意味着,光解离过程起到非常重要的作用。这是因为800 nm可以激发分子达到能够产生中性碎片的中间态。在400 nm时,虽然中间态的解离过程仍然至关重要,但并没有在800 nm时明显。综上所述,本文的研究证实了氯丙烯的光解离/电离行为具有波长依赖性,并揭示了氯丙烯在200、400和800 nm飞秒激光作用下的复杂动力学过程。     

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。     

Tandem mass spectrometric study of 1,3,5-trinitrobenzene molecular ion: an unusual ortho effect involving a hydrogen atom from the aromatic ring

Unimolecular (metastable) and collision-induced dissociation of 1,3, 5-trinitrobenzene molecular ion was studied using linked scans and mass-analyzed ion kinetic energy spectrometry on a hybrid instrument of EBEqQ geometry. An unusual ortho effect leading to the loss of OH radical from the parent molecular ion is observed as a unimolecular dissociation process only in the first-field free region between the ion source and the electric sector, although corresponding dissociation in the ion source is of negligible abundance (<0.1%). This unimolecular process is taken over by other dissociation pathways when the parent ion is collisionally activated, suggesting that this dissociation process occurs only in a very narrow energy window with a rate constant of the order of 2 x 10(5) s(-1). Copyright 2000 John Wiley & Sons, Ltd.     

Potentiometric and Thermodynamic Studies of 5-(4′-Sulfonylazidophenylazo)-3-phenyl-2-thioxothiazolidin-4-one and Its Metal Complexes

The proton dissociation constant of 5-(4-sulfonylazidophenylazo)-3-phenyl-2-thio- xothiazolidin-4-one (SPT) and the stability constants of its complexes with some metal ions were calculated potentiometrically in 0.1 M KCl and 40% (v/v) ethanol–water mixture. The order of stability was found to be Mn²⁺ < Co²⁺ < Ni²⁺ < Cu²⁺ < Zn²⁺. The effect of temperature on the dissociation of SPT and the stability of its complexes were studied. The corresponding thermodynamic functions were derived and discussed. The dissociation process is unspontaneous, endothermic, and entropically unfavorable. The formation of the metal complexes was found to be spontaneous, endothermic and entropically favorable.     

Collision-induced reactions of size-selected molecular cluster anions

Collision-induced reactions of size-selected cluster anions, (CO₂) _n ^? and (N₂O)_nO^? with He and Kr atoms were studied at collision energies from 0.1 to 2.0 eV (center-of mass) by means of a tandem mass-spectrometer equipped with a pair of octapole ion guides. The dominant process was evaporation of the constituent molecules from the parent cluster ion. The absolute cross section for the evaporation was measured as functions of the size of the parent cluster ion and the collision energy. The reaction was explained by collisional excitation of the parent cluster ion followed by its unimolecular dissociation. The observed cross sections which correspond to those for the collisional excitation agree with those calculated in terms of charge-induced dipole and induced dipole-induced dipole interactions between the parent cluster ion and the target atom. The distributions of the product ions resulting from the unimolecular dissociation were reproduced by a simple calculation based on RRK theory. In the collision of (CO₂) _n ^? , the cross sections for (CO₂) ₁₀ ^? and (CO₂) ₁₄ ^? were significantly small and their abundances in the product ion distributions were particularly large. These findings indicate that (CO₂) ₁₀ ^? and (CO₂) ₁₄ ^? are stable species. On the other hand, stable species in (N₂O)_nO^? was found to be (N₂O)₅O^?.     

Collisionally activated decomposition of poly(ethylene glycol)s: An investigation of high-mass ion abundances in the collisional activation technique with large molecules

The utility of the collisional activation technique in structure determination of ions is limited as parent ion mass increases. Optimum collisionally activated dissociation yield is often obtained at parent masses of 1000–2000 u, after which daughter ion yield decreases. The apparent decrease in the efficiency of the collisional activation process has been thought of as a degree-of-freedom effect: as new rotational-vibrational modes are added to the parent ion, its lifetime with respect to dissociation increases. We have investigated this effect using an easily characterized system of several poly(ethylene glycol) homologs from the 15-mer to the 35-mer. Observed trends in the collisional activation spectra as parent mass increases support the postulated ‘degree-of-freedom’ effect in general. The loss of C₂H₄O from the [M ? H]^? parents, a fragmentation which has a high activation barrier, however, actually becomes more favored as the parent ion becomes larger. This effect is explained in terms of statistical rate theory.     

Fragmentation dynamics of methane by few-cycle femtosecond laser pulses

The fragmentation pattern of CH4 was experimentally studied at an intensity of approximately 10(14) W/cm2 with laser durations varying from 8 to 110 fs. When the laser duration was 8 fs, only the primarily fragmental CH3+ ion was observed in addition to the parent CH4+ ion. When the laser duration was 30 fs, small fragmental CH2+ and H+ ions appeared. When the laser duration was 110 fs, some doubly charged ions were also observed in addition to the abundant singly charged ions. The large mass spectra difference demonstrated that the pulse duration had a strong effect on the fragmentation of the parent ion produced in the single ionization. The effect of laser intensity on the fragmentation of CH4+ was also studied for few-cycle femtosecond laser pulses. The results demonstrated that the first-return recollision between the rescattered electron and the parent ion played a significant role in the fragmentation dynamics of the parent ion. Depending on the ion-electron impact energy, the recollision excited the parent ion to a dissociated state or doubly charged state. The experimentally observed singly charged fragmental ions resulted from the recollision-induced dissociation of CH4+ or the Coulomb explosion of CH(4)2+.     

Equilibria in complexes of N-heterocyclic molecules,part XII. The reaction of hydroxide and alkoxide Ions with platinum(II) complexes of 5-nitro-1,10-phenanthroline and 2,2′-bipyridyl

Summary Bis-(5-nitro-1,10-phenanthroline)platinum(II) dichloride and diperchlorate have been prepared. The reaction between the parent cation and hydroxide ion has been studied using 1 FI n.m.r. spectroscopy and found to involve attack at the ligand. The bis-(2,2-bipyridyl)platinum(II) ion has been shown to be highly reactive towards methoxide ion. The dissociation of a 2,2-bipyridyl ligand is preceded by attack at the ligand.Part XI: R. D. Gillard, t.. A. P. Kane-Maguire and P. A. Williams,Transition Met. Chem., 2, 47 (1977).On leave from the University of Baghdad, Iraq.     

Polymerization of ethylene molecules chemisorbed on CrOH+ as a model system of chromium-containing catalyst

The reaction process of the production of CrOH(C2H4)2(+) was studied in connection with the ethylene polymerization on a silica-supported chromium oxide catalyst (the Phillips catalyst). Cluster ions CrOH(C2H4)2(+) and CrOH(C4H8)+ were produced by the reactions of CrOH+ with C2H4 (ethylene) and C4H8 (1-butene), respectively, and were allowed to collide with a Xe atom under single collision conditions. The cross section for dissociation of each parent cluster ion was measured as a function of the collision energy (collision-induced dissociation, or CID). It was found that (i) the CID cross section for the production of CrOH+ from CrOH(C2H4)2(+) increases sharply at the threshold energy of 3.16 +/- 0.22 eV and (ii) the CID cross section for the production of CrOH+ and C4H8 from CrOH(C4H8)+ also increases sharply at the threshold energy of 3.26 +/- 0.21 eV. In comparison with the calculations based on a B3LYP hybrid density functional method, it is concluded that two ethylene molecules in CrOH(C2H4)2(+) are polymerized to become 1-butene. The calculation also shows that the dimerization proceeds via CrOH(C2H4)+ (ethylene complex) and CrOH(C2H4)2(+) (ethylene complex), in which the ethylene molecules bind with CrOH+ through a pi-bonding.     

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.     

Determination of polychlorodibenzo-p-dioxins and polychlorodibenzofurans by gas chromatography/tandem mass spectrometry and gas chromatography/triple mass spectrometry in a quadrupole ion trap

The determination of tetra- to octachlorodibenzo-p-dioxins and tetra- to octachlorodibenzofurans (PCCD/Fs) by high-resolution gas chromatography/tandem mass spectrometry (HRGC/MS/MS) and high-resolution gas chromatography/triple mass spectrometry (HRGC/MS(3)) in a quadrupole ion trap, equipped with an external ion source, is presented. MS/MS involves a typical four-step process, namely ionization, parent ion isolation, collision-induced dissociation (CID) and mass analysis of the daughter ions. For the MS(3) experiment, the MS/MS scan function is used with the addition of selected daughter ion isolation, their CID and the mass analysis of second-generation product ions called 'grand-daughter ions.' For both methods, the energies necessary for the CID of the 17 PCDD/Fs were determined and optimized using multiple scan functions with different CID amplitudes. The CID efficiency, defined as the signal ratio of fragment ions detected from the major dissociation channels to molecular ions isolated, was 1.15-2.40 V for parent ion dissociation (MS/MS) and 1.05-1.50 V for daughter ion dissociation (MS(3)) and for all the chloro congeners. The same sensitivity (1 pg microl(-1)) can be reached with both the MS/MS and MS(3) methods and linear responses were obtained between 1 and 100 pg microl(-1) injected.     

Metastable and collision-induced fragmentation studies and thermochemistry of isomeric C(4)H(11)Si(+) ions and their adducts with C(4)H(12)Si silanes

Metastable Ion (MI) and collision-induced dissociation (CID) mass spectra for all isomeric even-electron [C(4)H(12)Si - H](+) ions were recorded and compared. Deuterium labeling experiments indicated that most precursors give rise to silylium ions. Silylium ions with two or more methyl groups are found to lose C(2)H(4) after isomerization via a straightforward hydrogen transfer to the appropriate ethylsilylium ion. Similarly, all isomeric propyl- and butyl-containing silylium ions are found to lose C(2)H(4) by rearrangement preceding dissociation. In the CI source of the mass spectrometer many of the silylium ions are found to cluster with the parent neutral silane present in the source to give stable [M - H](+)+M adduct ions. The MI and CID spectra of these adduct ions were also obtained. In the MI spectra of all adducts, except i-BuSiH(3), only the starting silylium ion is observed. Under CID conditions generation of silylium ions dominates. Deuterium labeling studies show that this dissociation may be accompanied by some rearrangement, in particular for the adducts from i-BuSiH(3). High-pressure mass spectrometric clustering equilibrium measurements were also carried out to determine the enthalpies and entropies of binding of the silylium ions to the neutral silanes. These measurements yield insight into the effects of various alkyl group substitutions on the association thermochemistry in these adducts. Copyright 2000 John Wiley & Sons, Ltd.