Optimization of a quadrupole ion storage trap as a source for time-of-flight mass spectrometry

Designs of a quadrupole ion trap (QIT) as a source for time-of-flight (TOF) mass spectrometry are evaluated for mass resolution, ion trapping, and laser activation of trapped ions. Comparisons are made with the standard hyperbolic electrode ion trap geometry for TOF mass analysis in both linear and reflectron modes. A parallel-plate design for the QIT is found to give significantly improved TOF mass spectrometer performance. Effects of ion temperature, trapped ion cloud size, mass, and extraction field on mass resolution are investigated in detail by simulation of the TOF peak profiles. Mass resolution (m/Δm) values of several thousand are predicted even at room temperature with moderate extraction fields for the optimized design. The optimized design also allows larger radial ion collection size compared with the hyperbolic ion trap, without compromising the mass resolution. The proposed design of the QIT also improves the ion-laser interaction volume and photon collection efficiency for fluorescence measurements on trapped ions.     

Cat's-eye reflectron

A new version of the non-magnet time-of-flight mass spectrometer reflectron is described. The method of operation, which allows to separate packets of ions with different masses both by their time-of-flight and by their deflection angle in the deflection system, the operation of which is synchronizes the arrival time of the ions with the focusing plane of this time-of-flight mass spectrometer is outlined.     

飞行时间质谱峰值的漂移

飞行时间质谱仪(time-of-flight mass spectrometer, TOF-MS)在分子团簇的激光电离/解离动力学研究中广泛使用。文章报道了在用脉冲355 nm的YAG激光进行水/甲醇二元团簇的多光子电离研究中,发现在电离激光相对于脉冲分子束的不同延时下,即激光作用于脉冲束的不同位置,飞行时间质谱仪测得的离子的质谱峰值发生漂移。在激光作用于脉冲束的中段时,离子的信号最强,同时离子的峰值漂移达到最大。分析认为：这种峰值漂移不是因为新质量数谱峰的出现,而是离子在穿越质谱仪的离子引出区和加速区极板时发生部分离子吸附,引起极板间电压的起伏造成的。离子在电场起伏下的数值模拟与实验中观测到的离子峰值漂移规律一致。     

Laser ion kinetics: set-up and application of a single-shot femtosecond pump–probe technique

In this contribution the first measurements of a single-shot femtosecond laser pump–probe technique are reported. The technique is based on counter-propagating femtosecond laser pulses in a supersonic beam of a low density of sample molecules and simultaneous probe detection by ion or fragment-ion formation through a reflectron time-of-flight mass spectrometer. It will be shown that the range of the pump–probe delays covers the time span between 100 fs and 10 ps depending on the pulse width of the laser used and the stability of the volt ages of the mass spectrometer. The application of this technique to organometallic compounds as well as to medium-sized organic molecules reveals some insight into the electron-transfer process during ionization through a 1+1 multi-photon absorption procedure. Furthermore it is demonstrated that this technique is also applicable to the investigation of ultra-fast isomerization and fragmentation processes. As an example the results of the processes within iron pentacarbonyl and substituted benzalacetones are reported. Received: 22 October 1999 / Published online: 24 July 2000     

Analytical method for computing the electrostatic field distribution in the reflector of the time-of-flight mass spectrometer

The method of analytical calculation of a nonlinear electrostatic mirror of the time-of-flight mass spectrometer and the numerical method of computation of a nonlinear mirror are analyzed. We present the results of simulating of the devices with nonlinear focusing mirrors, which are calculated analytically and by the numerical method, and of the device with a linear reflectron. It is concluded on the basis of the results of simulation that the proposed analytical method for calculating a nonlinear electrostatic mirror of the time-of-flight mass spectrometer is much better than the existing numerical method.     

Dissociation of Cyclotrimethylenetrinitramine Under 1064-nm Laser Irradiation Investigated by Time-of-Flight Mass Spectrometer

Laser-induced dissociation pathways of cyclotrimethylenetrinitramine have been investigated with a focused laser of 1064 nm by use of a time-of-flight mass spectrometer. The ions produced from the cyclotrimethylenetrinitramine surface were detected and the mass spectra of both positive and negative ions were obtained. According to the possible distribution of the decomposition products, possible dissociation paths of cyclotrimethylenetrinitramine were proposed. The influence of the intensity and the delay time of the laser beam to the decomposition have also been studied. The results may possibly throw some light on our understanding of the reactions taking place in laser ignition.     

用于团簇研究的激光反射式飞行时间质谱仪

报道了新建造的用于团簇研究的反射式飞行时间质谱仪 ,包括反射式飞行时间质谱仪的结构、原理、真空系统、控制系统等 .初步性能测试表明 :激光溅射 /分子束载带型团簇离子源能够产生丰富的一元、二元团簇离子 ;质谱仪对离子的质量分辨接近 2 0 0 0 ,并且质量门也有较高的质量选择性 .系统用于团簇研究 ,得到了一些初步实验结果 .     

XeCl准分子激光诱导的氮分子多光子电离

本文采用分子束和改装过的质谱装置,进行了氯化氙准分子激光诱导的氨分子紫外光电离的研究。我们不仅在(m/e)=16,17处分别观察到NH_2~+和NH_3~+离子峰,而且还在(m/e)=18处观察到NH_4~+离子峰。为搞清各种离子特别是NH_4~+离子的产生机理,测量了各种离子产率与样品压强和激光功率的依赖关系。     

紫外激光作用下环氧乙烷的TOF质谱研究

本文采用超声分子束技术,分别在308nm和355nm的紫外激光下,对环氧乙烷分子进行了多光子电离飞行时间(TOF)质谱研究.在308nm激光作用时,观测到C_2H_4O~+、C_2H_3O_+、CHO~+和CH_3~+等离子的信号;在355nm激光作用时,则没有观测到分子离子的信号.在两种激光作用下最强的信号都是CHO~+.但是两种激光下各碎片离子信号的光强指数有一定差别,表明在两种情形下,环氧乙烷分子经历了不同的电离解离过程.     

Laser spectroscopy on molecular beam with a time-of-flight mass spectrometer operating in a strong magnetic field

Experimental set-up for studying effects of a strong magnetic field on a structure and a decay dynamics of molecules, was designed and constructed. A vacuum chamber, in which a molecular beam propagated, was mounted in a bore of a superconducting magnet. Laser light crossed the molecular beam in the magnetic field and excited the molecules. Fragment or parent ions produced through sequential decay processes, were extracted by an electric field parallel to the magnetic field and detected by a microchannel plate. By measuring the time-of-flight from the photo-excitation to the ion-detection, a species of ions —mass and charge state— was identified. A performance of the set-up was demonstrated using the resonance enhanced multiphoton ionization process through the X²Π-A²Σ⁺ transition of nitric oxide (NO) molecules. A mass resolution m/Δm ≥180±6 was obtained in the field up to 10 T. This was the first successful result demonstrating the sufficient mass resolution obtained by the time-of-flight technique in the strong magnetic field up to 10 T. Parent NO⁺ ions were selectively detected by the mass spectrometer and the ion current was measured as a function of the frequency of the laser light. Rotational transition lines were measured with a sufficient S/N ratio in the field up to 10 T.     

离子光学系统简单数值计算方法在反射式飞行时间质谱仪中的应用

简要阐述了求解离子光学系统电场结构分布以及带电粒子在该电场中运行轨迹的通用数值计算方法,分析了在保证计算精度的前提下,节省磁盘空间、提高计算速度的PC级计算机上优化算法,并提出一种寻找最佳超松弛因子的可行性方法.在PC级计算机上应用该计算方法对一台无栅网结构高分辨率反射式飞行时间质谱仪进行计算,给出了电场分布、粒子飞行轨迹和设定各种不同条件对电场进行优化的结果.根据计算结果调整的反射式飞行时间质谱仪达到了其优化工作状态,所测得的质谱分辨率显著提高.     

飞行时间质谱仪中激光解离的Ni^＋与醇类化合物分子束流气 …

将分子束流,激光解离和飞行时间质谱结合起来,在一个石英反应室内,让激光解离的Ｎｉ＾２＋与连续喷入的醇分子不流发生反应,产物经飞行时间质谱仪检测,研究了Ｎｉ＾＋一Ｃ２～Ｃ６等五种醇分子的气相反应。用如下的插入机理解释反应：（１）选择性的插入醇分子共价键;（２）β－Ｈ迁移至Ｎｉ＾＋;（３）失去一中性分子形成产物离子。     

Fe（CO）5双色共振增强多光子电离研究

利用超声分子束、强激光多光子电离和飞行时间质谱探测装置研究了Fe(CO)_5分子在355nm、532nm和355nm+532nm单、双色激光作用下的多光子电离质谱.实验结果证明了双色激光的共振增强电离作用.由飞行时间质谱的展宽峰型结构估算了Fe(CO)_5等分子的光解离寿命与Fe~+和Fe(CO)_5离子分子反应截面.     

氯苯的同步辐射光电离研究

利用真空紫外同步辐射和反射式飞行时间质谱仪对氯苯进行了光电离研究,通过测量各离子的光电离效率(PIE)曲线,得到了氯苯的电离势为(9.11±0.05)eV及两种主要碎片离子C6H+5和C4H+3的出现势分别为(12.96±0.05)和(16.27±0.05)eV.结合有关文献的热力学数据,推导出C6H5Cl+、C6H+5及C4H+3的离子生成焓及一些键的解离能.实验获得了118.0nm同步辐射光电离下氯苯的质谱图.     

激光烧蚀Al等离子体与甲醇团簇反应中(CH3OH)nCH3O-的形成

激光烧蚀一分子束(LA-MB)法是研究金属离子与分子团簇反应的有效方法.在气相条件下,用飞行时间质谱观测到激光烧蚀Al等离子体与脉冲分子束超声膨胀产生的甲醇团簇碰撞反应生成的(CH30H)nCH3O-(n=3～23)团簇负离子.实验发现,此序列的团簇负离子主要生成于烧蚀激光作用于脉冲分子束的后段,(CH3OH)3CH3O-离子强度始终远远大于其后的离子,并且这些离子随尺寸大小的分布变化平缓.结合量化计算,在133LYP/6-31G(d)水平上得到(CH3OH)nCH3O-(n=1～4)的可能几何构形,并推断(CH3OH)3CH3O-为-幻数结构.     

自由钨团簇与氮分子反应性的尺寸相关性

用激光蒸发团簇源产生Wn团簇束 ,团簇通过一个充有N2 气体分子的低压反应池 ,利用飞行时间质谱探测反应产物 ,在单次碰撞条件下研究了W+ 10 —W+ 50 和N2 分子的反应性 ,在室温条件下测量了N2 分子与W+ n 团簇反应的反应几率 .n =10— 2 6的团簇与N2 分子的反应几率与团簇尺寸有很强的相关性 ,n =16 ,2 2 ,2 3的团簇有较高的反应性 .W+ n 与N2 分子的反应性与Wn与N2 分子的反应性显示出相似的规律性. A beam of tungsten clusters, seeded in He gas, is produced in a pulsed laser vaporization source. We have studied the size-dependent reactivity of positive tungsten cluster ions with N 2 under single-collision conditions by using laser-vaporization source, low-pressure reaction cell and time-of-flight mass spectrometer. The reaction probability with N 2 molecule was measured as a function of cluster size, W + 10-W + 50, for clusters produced at room temperature...     

532 nm激光作用下CH3I分子的多光子电离

利用飞行时间质谱仪在超声射流冷却条件下探讨了532 nm激光作用下CH3I分子的多光子电离(MPI)解离过程和机制,得到了分子的飞行时间质谱,质谱中包含较强的I 、CH3 离子信号和较弱的CH3I 、CHn (n≤2)、C 、H 离子信号.不同激光能量下的质谱信号在排布上相似,但在强度上有差别.在532 nm激光作用下CH3I分子的多光子电离包括两个过程:一是CH3I分子由双光子激发到A带解离,生成I原子和CH3基团,然后再吸收光子实现中性碎片电离;另一通道是CH3I分子由三光子共振激发到里德堡C态,处于激发态的母体分子继续吸收两个光子电离形成母体离子,碎片离子可由母体离子解离形成.     

A1等离子体与甲醇团簇的反应

利用激光烧蚀-分子束法(LA-MB)对激光烧蚀金属铝靶产生的Al等离子体与脉冲分子束超声膨胀产生的(CH3OH)n团簇在气相条件下的反应进行了研究.烧蚀激光相对于脉冲分子束之间的延时不同,观测到团簇离子序列及团簇尺寸的变化,反映出脉冲分子束状态对反应条件及激光烧蚀等离子体状态的影响.在激光烧蚀发生于脉冲分子束的前段,主要反应产物为Al (CH3OH)n,但团簇尺寸较小;在烧蚀发生于脉冲分子束的中段,主要产物为H (CH3OH)n,团簇尺寸增大,强度减弱;在烧蚀发生于脉冲分子束的后段,观测到尺寸更大的水合质子化团簇H (H2O)m(CH3OH)n.结合团簇离子速度分布的特征,对团簇的产生机理进行了讨论.     

纳秒强激光中乙腈团簇增强的高价电离研究

利用脉宽为25 ns的脉冲Nd∶YAG 1 064 nm的激光,在1010～1011 W·cm-2的强度下,用飞行时间质谱对乙腈分子束激光电离过程进行了研究。实验中利 用氦气作为载气,乙腈分子束采用扩散和脉冲两种方式进样,当扩散束进样时,乙腈分子的谱峰可用多光子电离来解释,而当脉冲分子束进样时,实验中产生了外层价电子高剥离的Nq+ (q=2～5) 和Cq+(q=1～4)信号谱。实验中同时发现,激光波长增大时,高价离子的谱强度也趋向于增大。激光延迟及谱峰的相关性分析表明,这些高价离子可能来源于乙腈团簇的库仑爆炸 过程。提出一个多光子电离引发,逆韧致吸收加热-电子碰撞电离模型来解释高价离子的产生,对高价离子伴随的波长效应也给出了较为合理的解释。     

410～355 nm内四甲基硅的多光子解离和电离研究

利用平行板电极装置研究了四甲基硅在410～378 nm内的MPI光谱;利用TOF质谱仪研究了该分子在402～371 nm内若干个波长点处的TOF质谱;利用四极质谱装置研究了它在355 nm处的MPI质谱.测得了355 nm下Si(CH3)+n(n=1,2,3,4)及Si+的激光光强指数,以及其信号强度占总信号强度的分支比随光强的变化关系.据此,讨论了该分子MPI过程的可能通道,得出了Si+主要来自于母体分子的多光子解离-硅原子的电离、Si(CH3)+n(n=1,2,3)主要来自于Si(CH3)n(n=1,2,3)的自电离、Si(CH3)+4来自于母体分子的(3+1)电离的结论.