Identification of isomers and control of ionization and dissociation processes using dual-mass-spectrometer scheme and genetic algorithm optimization

Identification of acetone and its two isomers, and the control of their ionization and dissociation processes are performed using a dual-mass-spectrometer scheme. The scheme employs two sets of time of flight mass spectrometers to simultaneously acquire the mass spectra of two different molecules under the irradiation of identically shaped femtosecond laser pulses. The optimal laser pulses are found using closed-loop learning method based on a genetic algorithm. Compared with the mass spectra of the two isomers that are obtained with the transform limited pulse, those obtained under the irradiation of the optimal laser pulse show large differences and the various reaction pathways of the two molecules are selectively controlled. The experimental results demonstrate that the scheme is quite effective and useful in studies of two molecules having common mass peaks, which makes a traditional single mass spectrometer unfeasible.     

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.     

Photodissociation of sodium iodide and resonant ionization of sodium atom produced

Resonant ionization spectroscopy (RIS) and resonant ionization mass spectroscopy (RIMS) are employed to detect the photodissociation product of sodium iodide molecules in a molecular beam in an intense laser field in the absence of the buffer gases. Time of flight mass spectra is recorded. In particular, the appearances of multiphoton ionization are discussed.     

Photodissociation of RbI in an Intense Laser Field: Detection of the Product Metal Atom Rb Using RIMS

It is reported on the recent research using resonant ionization spectroscopy (RIS) and resonant ionization mass spectroscopy (RIMS) to detect the photodissociation product of Rubidium iodide molecules in a molecular beam in an intense laser field. Time of flight mass spectra is recorded. In particular, the appearances of multiphoton ionization are discussed.     

NH_3多光子电离和裂解动力学过程分析

本文分析了在XeCl准分子激光作用下NH_3分子的多光子电离质谱形成机理。所建立的动力学模型包括主要由经过中间态(6)和(1)的(2+1)共振多光子电离,生成NH_3~+;离子-分子反应形成大量的NH_4~+;经(6)态的(2+2)共振多光子电离,可能产生低产额的NH_2~+。这个模型的速率方程解与实验测量符合得很好,并在离子流强度对激光脉冲宽度的依赖关系中预示直接电离或间接电离机制的信息。     

Photodissociation of RbI in an Intense Laser Field: Detection of the Product Metal Atom Rb Using RIMS

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Influence of the photoionization process on the fragmentation of laser desorbed polycyclic aromatic hydrocarbons

Characterization of polycyclic aromatic hydrocarbons (PAHs) samples has been performed by laser desorption combined with multi-photon ionization technique using two different geometries of the ionization laser beam. This comparative study evidences the strong influence of ionization laser fluence on PAH fragmentation. Through a ∼10³ enlargement of the ionization probe volume and 10⁴ reduction of laser fluence over previous studies, fragment free mass spectra are obtained with higher sensitivity and selectivity. The ability to measure fragment free PAH mass spectra is a very important step in the end goal of measuring complex unknown mixtures of PAH desorbed from solid surface such as soot samples.     

Reliable Comparison of Electron Ionization Mass Spectra Recorded Under Identical Experimental Conditions

For the most reliable identification by means of electron ionization mass spectrometry, the full mass spectra of unknown compound and possible candidate should be recorded under identical experimental conditions and compared. The main problem is how to compare full mass spectra, which may contain a lot of peaks. We have proposed a new approach (based on using principal component analysis) for the reliable comparison of electron ionization mass spectra recorded under identical experimental conditions. Applicability of the approach has been demonstrated on the example of xylenol isomers.     

Laser Desorption Mass Spectrometry of Underivatized Bile Acids

Bile acids are important in the diagnosis of certain diseases. Their mass spectra are usually obtained by electron impact or chemical ionization and are dominated by fragment ions. We have investigated laser desorption (LD) as an ionization method for these compounds. The LD mass spectra contain abundant positive and negative quasimolecular ions. Bile acid salts can be successfully analyzed. In addition, the results help to elucidate details of the LD process.     

分子的飞秒强光电离

文章以一个实验者的角度，介绍了分子的飞秒强光电离的研究现状。文章从对比飞秒激光电离质谱与纳秒激光电离质谱开始，接着介绍分子在激光场作用下的可能电离机理，着重描述了几个处理分子场致电离的理论模型和实验验证，最后对飞秒激光导致的分子在激光脉冲作用后取向研究进行了简单介绍。     

激光诱导Fe^＋和Fe（CO5）离子分子反应机制的实验和理论研究

利用超声分子束和飞行时间质谱检测系统,实验研究了Fe(CO)_5在308nm,355nm和355nm+532nm波长的多光子解离和电离机制.根据实验测量和对于质谱峰结构和峰型的分析分离出由不同机制产生的各离子信号.对于Fe~+和Fe(CO)_5离子分子反应机制及其关于激光波长的依赖关系.从实验和理论两方面做了较深入的研究.     

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.     

Strong field ionization by ultrashort laser pulses: Application of the Keldysh theory

Analytical expressions and numerical results describing ionization of atoms by intense linearly polarized ultrashort laser pulses are obtained in the frame of the Keldysh approach. Photoelectron spectra and total ionization probabilities are presented for several analytical models of a single-cycle laser pulse. In particular, strong left-right asymmetry of the spectra is shown for the case of odd pulses.     

Determination and analysis of opiates in complex mixtures by surface-ionization mass spectrometry

The results of studies of the analytical opportunities of surface-ionization mass spectrometry (SIMS) for high-sensitivity and selective detection and analysis of opiate mixtures—natural opium, crude heroin, and narcotic analgesic omnopon—are presented. The experiments were carried out using an MX-1320 chemical mass spectrometer modernized for studying surface ionization (SI). It was ascertained that the opiate mixtures are ionized by highly efficient surface ionization. The bands of M⁺ (for papaverine), (M-H)⁺, (M-H-2nH)⁺, (M-R)⁺, and (M-R-2nH)⁺ ions, where M is a molecule, H is a hydrogen atom, R is a radical, are observed in the mass spectra; they are the sum of the SI mass spectra of components of the mixtures. The series of bands of ions with m/z of 144 and 146 that is characteristic of SI-morphinelike molecules is the main one in the mass spectrum of crude heroin, while for omnopon and natural opium this series is the main at low temperatures of a thermionic emitter (up to ∼900 K). At high temperatures of the thermionic emitter, the band series with m/z of 218 and 220 is the main series. Studies of natural opium, crude heroin, and omnopon have shown that the SIMS method allows analyzing mixtures without preliminary chromatographic separation thereof. The study also contains the results of comparative analyses of opiate mixtures by SIMS and chromate- and mass spectrometry (HP-6890) with electronic ionization.     

Plasma desorption mass spectroscopy of thiol-passivated gold nanoparticles

Plasma desorption mass spectrometry has been applied to characterization of dodecanthiol-passivated gold nanoparticles. An overview of the experimental set-up and mass analyses for the nanoparticles prepared in different conditions are shown. Mass distributions were found to shift to higher mass regions with increasing reaction temperature and reaction period. The results are consistent with those of transmission electron microscopy observations, UV-visible absorption spectra and also with a reported laser desorption mass spectrometry.     

邻溴甲苯多光子电离质谱及从头算

在波长为266 nm激光作用下，利用激光质谱法，得到了邻溴甲苯分子的多光子电离飞行时间质谱。通过分析部分碎片离子占总离子信号的分支比对激光强度的依赖关系，得出邻溴甲苯的多光子电离过程主要是母体分子解离-中性碎片电离。母体分子的解离主要有直接解离和先异构后解离两个可能的通道，对C7H7+、 C6H+、C5H5+等碎片离子的可能形成过程进行了讨论，并利用从头计算法对邻溴甲苯光解过程中的氢原子迁移反应作了理论验证。     

Ultra-fast laser pulses provide an ion source for highly selective mass spectroscopy

The mass spectra of two isomers of butane, 1-butene and cis-2-butene, interacting with linearly polarized Ti:sapphire laser pulses, were compared. It was demonstrated that the difference between the two spectra are much more pronounced than the corresponding spectra prepared by 100 eV electron ionization ion source. In addition, the difference could be varied by changing the peak laser intensity. The observation suggests potential application of dissociative multiphoton ionization by ultrafast laser pulses as a source for high performance mass spectroscopy.     

包含自电离过程的阈上离化

多电子原子都存在自电离过程,本文研究了存在自电离时的阈上离化过程,利用一个简化模型得到了光电子谱的解析表达式。结果表明,自电离的存在使阈上离化过程更为复杂,导致许多新现象的产生。 关键词：     

REMPI as a tool for studies of OH radicals in catalytic reactions

2 +? O₂→H₂O on polycrystalline Pt foils has been studied by detection of desorbing OH radicals using the Resonance Enhanced Multiphoton Ionization, REMPI, technique. The measurements were performed at catalyst temperatures of 1000–1400 K and a total pressure below 10^-4 mbar. The studies of OH desorption by REMPI were achieved using a two-photon excitation D²Σ^-–X²Π (1–0), followed by one-photon ionization. The ions were detected in a time-of-flight mass spectrometer, TOF-MS, in order to avoid interference from non-resonantly ionized molecules. By applying TOF-MS, a simultaneous non-resonant ionization and detection of H₂, O₂ and H₂O was achieved. Recorded REMPI spectra were compared with spectra simulated using known molecular constants. The kinetics of the reaction derived from the measurements were compared with what was obtained in earlier LIF detection of OH, performed at higher total reactant pressure using the A–X transition. REMPI TOF-MS is shown to be a complement to LIF for reaction studies below 5×10^-4 mbar total pressure, where LIF is too insensitive for quantification. The reaction kinetics was found to be in agreement with a theoretic model and previous LIF studies. Received: 8 March 1996/Revised version: 4 October 1996     

苯的同步辐射光电离效率谱的研究

用合肥国家同步辐射实验室光化学站的实验装置研究了苯分子的光电离质谱，从所得光电离效率谱精确地定出了苯分子的电离势及苯离子的出现热，并首次报道了三个苯离子的离解能。