两种氨基酸中[MH-CO2H2]+的特征质谱碎裂

运用低能碰撞诱导解离（ＣＩＤ）研究了电子轰击（ＥＩ）、快原子轰击（ＦＡＢ）电离条件下质子化亮氨酸与异亮氨酸解离产生亚稳离子「ＭＨ－ＣＯ２Ｈ２」的单分子质谱破裂，二种异构体呈现出了各自不同的解离特征，根据ＣＩＤ的特征碎片离子和氘代同位素标记实验，提出了其破裂过程的存在离子／中性（碎片）复合物中间体机理，并对有关的特征离子的形成进行了讨论。     

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。     

C4H5N-(NH3)n氢键团簇的多光子电力与从头计算

在３５５和５３２ｎｍ激光波长下用ＴＯＦ质谱仪研究了Ｃ４Ｈ５Ｎ－（ＮＨ３）ｎ系列氢键团簇体系的多光子电离,实验发现,两波长下除了得到一系列团簇离子Ｃ４Ｈ５Ｎ－（ＮＨ３）ｎ＾＋外,还观测到一系列质子化产物Ｃ４Ｈ５Ｎ－（ＮＨ３）ｎ－Ｈ＾＋,这些质子化产物来自于光电离过程中团簇内部的质子转移反应;Ｃ４Ｈ５Ｎ－（ＮＨ３）ｎ＾＋系列离子出现反常强度变化,即Ｃ４Ｈ５Ｎ－（ＮＨ３）２＾＋离子强度较Ｃ４Ｈ５Ｎ－（Ｎ     

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。     

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.     

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。     

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…     

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。     

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。     

3种羧酸类基质的基质辅助激光解吸／电离质谱行为

１引言基质辅助激光解吸／电离质谱（ＭＡＬＤＩ－ＭＳ）这种新的“软电离”质谱技术，能够在短短１０年间，得到广泛应用与迅速发展，很大程度上要归功于基质的辅助效应。基质在样品的解吸／电离过程中，起着关键作用。对基质本身ＭＡＬＤＩ－ＭＳ的研究，不仅可以、刻认识ＭＡＬＤＩ－ＭＳ中离子生成、碎裂的机制，在低分子量物质分析时更是必不可少。我们选择常用的３种羧酸类基质：２，５－二羟基苯甲酸（２，５－ＤＨＢ）、芥子酸（ＳＡ）、α－ＣＮ－４羟基肉桂酸（ＡＣＨＣ），进行了其自身ＭＡＬＤＩ－ＭＳ的研究。２实验部分２．１…     

Determination of unimolecular ionic formation rates by pulsed laser-linear reflectron time-of-flight mass spectrometry

The study of fragment-ion signals as a function of delay time between the laser pulse and the pulsed extraction electric field in a linear reflectron offers a new technique for the determination of the formation rates of some of these fragments. It is shown that this technique has better time resolution, higher sensitivity, and more versatility than previous methods. The formation rates of seven daughter ions resulting from laser multiphoton ionization dissociation (MPID) of 1,4-dichlorobenzene are determined. The formation rate of C₆H₄C1⁺ at high laser intensities is comparable to that determined using one 14 eV photon. This suggests that its formation by MPID at high UV intensity involves the three-UV-photon level (at 14.0 eV) via a ladder mechanism.     

Femtosecond real-time probing of transition state dynamics in a surface photoreaction: methyl desorption from CH3I on MgO(100)

A novel experimental approach to the investigation of surface adsorbate reaction dynamics is presented. The direct time-resolved monitoring of the surface reaction transition state and product formation dynamics were accomplished via pump-probe mass spectrometry. As an example, methyl iodide molecules adsorbed at submonolayer coverage on an ultrathin magnesia film on Mo(100) were photoexcited to the A-band by ultrafast laser pulse irradiation. Employing time-delayed multiphoton ionization the dynamics of the dissociative methyl iodide transition state and of the emerging methyl photoproduct could be detected with femtosecond resolution. The reaction times deduced from the temporal evolution of the methyl ion mass signal indicate a strong interaction of the methyl fragment with the substrate surface prior to desorption.     

The primary step in the ultrafast photodissociation of the methyl iodide dimer

This paper shows the results of combined experimental and theoretical work that have unravelled the mechanism of ultrafast ejection of a methyl group from a cluster, the methyl iodide dimer (CH(3)I)(2). Ab initio calculations have produced optimized geometries for the dimer and energy values and oscillator strengths for the excited states of the A band of (CH(3)I)(2). These calculations have allowed us to describe the blue shift that had been observed in the past in this band. This blue shift has been experimentally determined with higher precision than in all previously reported experiments, since it has been measured through its effect upon the kinetic energy release of the fragments using femtosecond velocity map imaging. Observations of the reaction branching ratio and of the angular nature of the fragment distribution indicate that two main changes occur in A-band absorption in the dimer with respect to the monomer: a substantial change in the relative absorption to different states of the band, and, more importantly, a more efficient non-adiabatic crossing between two of those states. Additionally, time resolved experiments have been performed on the system, obtaining snapshots of the dissociation process. The apparent retardation of more than 100 fs in the dissociation process of the dimer relative to the monomer has been assigned to a delay in the opening of the optical detection window associated with the resonant multiphoton ionization detection of the methyl fragment.     

Photoelectron imaging of atomic iodine following A-band photolysis of CH3I

Photoionization of the iodine atom following methyl iodide A-band photodissociation was studied over the wavelength range of 245.5-261.6 nm by photoelectron imaging technique. Final state-specific speed and angular distributions of the photoelectron were recorded. Two types of the photoelectron resulted from ionizing the I atom from the photodissociation of CH3I were identified: (a) (2+1) REMPI of the ground state I atom, and (b) two-photon excitation of spin-orbit excited I(2P1/2) to autoionizing resonances converging to the 3P1 state of I+. In addition, some weaker signals were attributed to one-photon ionization of I atoms produced in some higher excited states from multiphoton ionization of CH3I followed by dissociation. Analysis of relative branching ratios to different levels of I+ (in case a) revealed that the final ion level distributions are generally dominated by the preservation of the ion-core configuration of the intermediate resonant state. A qualitative interpretation of the electron angular distribution from an autoionization process is also given.     

Velocity Mapping Studies of Vibrational Energy Disposal Following Methyl Iodide Photodissociation

In this paper previous results are compared for two different types of velocity mapping studies which probe vibrational energy disposal following the A-band photodissociation of methyl iodide, CH₃I + hv → CH₃ (v) + 1(²P_3/2), 1*(²P_1/2). Full three-dimensional state-specific speed and angular distributions of the nascent fragments have been recorded for the photoelectrons, iodine atoms, and methyl radicals, using state- and mass-selective (2+1) resonance-enhanced multi-photon ionization (REMPI)/time-of-flight spectrometry. Two sources of information on the vibrational energy disposal are available from velocity mapping: (a) the photoelectron images, which give information on the initial stages of vibrational excitation in electronically excited CH₃I, and (b) methyl radical images, which indicate the final energy disposal channels. Even though the two signals are believed to probe very different time-scales of the dissociation process, good agreement between the two is found for the vibrational energy disposal trends. Several trends found in the data for methyl iodide photodissociation indicate that readjustment of the ab initio multi-dimensional potential energy surfaces calculated for this molecule appears to be needed.     

Near-UV photodissociation of oriented CH3I adsorbed on Cu(110)-I

Methyl iodide adsorbed on a Cu(110)-I surface has been found to be highly orientationally ordered. We have exploited this orientation to select different CH(3)I excited states for photodissociation by using polarized near-UV light at wavelengths of 308, 248, and 222 nm. Using p-polarized light at all three wavelengths, we find that dissociation proceeds largely via the (3)Q(0) state, consistent with the picture from gas-phase photolysis. In contrast, using s-polarized light we find contributions from the (3)Q(1) state at lambda=308 nm, the (1)Q(1) state at lambda=248 nm, and the (E,1) state at lambda=222 nm-the latter being a state that has not been implicated in gas-phase studies of CH(3)I A-band photolysis. We also note the contribution to surface photodissociation from low-energy photoelectrons causing dissociative electron attachment to adsorbed CH(3)I and have identified the promotion of direct photodissociation pathways during lambda=308 nm photolysis.     

Mass resolved MPI spectra of methyl iodide in the 430-490 nm region

The mass resolved multiphoton ionization (MPI) spectra of methyl iodide were obtained in the 430-490 nm region using a time-of-flight (TOF) mass spectrometer. They have the same vibrational structure, which testifies that the fragment species, in the wavelength region under study, are from the photodissociation of multiphoton ionized molecular parent ions. Some features in the spectra are identified as three-photon excitations to 6p and 7s Rydberg states of methyl iodide. Two new vibrational structures of some Rydberg states are observed. The mechanism of ionization and dissociation is also discussed.     

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.     

氟硼二吡咯类pH荧光探针PET光谱特性的理论计算

氟硼二吡咯(BODIPY)类pH荧光探针分子是基于光诱导电子转移(PET)的荧光探针分子, 识别基团氮原子上引入不同取代基可呈现不同的光学灵敏度. 本文应用密度泛函理论(DFT)及含时密度泛函理论(TD-DFT)方法对六种含不同取代基的探针分子进行了几何构型优化及激发态计算, 探讨了不同取代基对PET效应影响. 计算结果表明: 基态时这些探针分子的最高占有分子轨道(HOMO)和最低未占有分子轨道(LUMO)都在荧光母体BODIPY的π, π^*轨道, 而识别基团上氮原子孤对电子所在的轨道为HOMO-1轨道. 但是在激发态, 当氮原子上有两个取代基时, HOMO-1→LUMO跃迁的激发能都小于荧光团的HOMO→LUMO跃迁, 这将有可能产生PET效应并导致荧光熄灭, 而当氮原子上有一个取代基时不会出现这种现象. 通过激发态结构优化可以发现, 无论识别基团氮原子上有一个还是两个取代基, N原子的轨道对称性都发生变化, 由sp³→sp², 孤对电子占据在p轨道上, 其轨道能级升高至荧光团的HOMO和LUMO轨道之间, 将导致不同程度的PET效应, 与实验结果一致.