纳秒强激光场中苯电离产生高价离子的研究

用25 ns脉冲Nd-YAG 532 nm的激光，在1010～1011 W•cm－2的光场强度下，利用飞行时间质谱对He、 N2、Ar载气条件下苯的激光电离过程进行了研究.发现当利用氩作为载气时，除观察到C2＋、C2H2+、C3H3+、C6H6+离子外，还观察到很强的Cq＋(q=1～3)高价离子.这些离子都有很高的平动能， C2＋的最可几平动能为12.9 eV， C3＋为37.5 eV.通过改变载气种类和压力及在不同光场强度条件下的实验，可以认为这些高价离子来源于含苯团簇的库仑爆炸过程.     

532 nm纳秒激光电离产生Xez＋(z ≤ 11)高价离子

利用25 ns脉冲Nd-YAG 532 nm激光,在1011 W•cm－2的光场强度下,研究了Xe原子团簇的激光电离过程,观察到较强的高价离子信号,其中最高价态达＋11.不同脉冲束位置和束源压力的实验表明,仅当激光作用于脉冲束中段时才能观察到高价离子,且高价离子信号强度随束源压力的增加而迅速增强,说明束中大尺寸团簇的存在与高价离子的形成密切相关.通过实验,认为高价离子可能来源于电离原子团簇而形成的纳米尺度等离子体小球对激光光场的共振吸收.     

纳秒激光电离产生Kr17+的研究

Up to Kr17 + multicharged krypton ions have been observed in time-of-flight mass spectrum by a 25 ns Nd-YAG 1. 064 μm laser at laser intensity about 1012 W/ cm2 . Experimental results indicate that the multicharged ions appear only when the laser interacts with the middle part of the pulsed beam,and the intensities of the multicharged ions increase dramatically by increasing the backing pressure of Kr gas,which indicates that the clusters in the beam is essential to the production of multicharged ions. From the experimental results,it is concluded that the cluster is ionized via multiphoton ionization and forms a nanoplasma ball,which can absorb the laser resonantly to further ionize the single charge ion to the high charge state.     

乙腈团簇增强的激光高价电离现象的质谱研究

利用脉宽为25 ns的脉冲Nd：YAG1064 nm激光, 在10¹⁰～10¹¹ W•cm^－２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, 发现了高价态的原子离子N^q+(q＝1～5)和C^q+(q＝1～4). 类氦离子N⁵⁺、C⁴⁺的最可几平动能分别高达566 eV和427 eV. 激光延时以及不同束源压力的实验结果表明, 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.     

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.     

纳秒强光场下呋喃的激光电离中高价离子的产生

The photo ionization of furan by an intense 25 ns Nd:YAG 532 nm laser has been studied by time-of-flight mass spectrometry. At the laser intensity of 1010～1011 W/cm2, multi-charged ions Can+ (n=2～4) and Ohm+ (m=2～3) appeared in the mass spectra when argon was used as the carrier gas. From the peak splitting and the numeric analysis, the most probable kinetic energies of C2+, C3+ and C4+ were confirmed to be 21、63 and 100 eV respectively, and the most probable kinetic energies of O2+ and O3+ were confirmed to be 20 and 40 eV respectively. It is proposed that the multi-charged ions come from the Coulomb explosion of furan cluster ions produced by multi photon ionization of neutral furan cluster.     

激光解吸电离飞行时间质谱下的银簇行为

近年来,对金属簇的研究已成为化学与物理学中最活跃的研究领域之一［１］．金属簇被认为是介于单个原子与固体之间的中间相［２］．深入地研究其结构、形成机理及物理与化学行为,对于寻找新的催化剂［３］,重新认识气相化学与凝聚相化学的关系［４］,都有非常重要的意...     

激光等离子体中超金属氧化物离子LiZnO+的产生

作为一般规律 ,在一些具有热力学稳定性的氧化物分子中 ,氧原子周围共价电子数为 8.自从发现 Li3O和 Li4 O分子以来 ,这类超过 9个或更多共价电子的含金属团簇小分子呈现出来的特殊化学计量比和热力学稳定性引起人们的关注 ,人们称其为超共价分子 (Hypervalent Molecules)或超金属分子(Hypermetallic Molecules) [1～ 4 ] .目前 ,在实验上已发现了 Mn O,Mn S及 Mn C(M=Li,Na,K,Mg;n≥ 3 )等一系列超金属分子 ;在理论上 ,从头计算法已可计算出超金属分子的结构及其稳定性 ,使人们对这些超金属分子的产生与结构有一定的认识 .然而 ,由…     

表面辅助激光解吸电离-飞行时间质谱中多聚体离子产生规律的研究

表面辅助激光解吸电离质谱(SALDI-MS)已经成为固态、液态样品分析的重要手段,并且分析对象逐渐由生物大分子扩展到小分子.然而,对小分子电离微观反应机理的研究仍处于起步阶段.本研究选择3种分子结构相似的稠环芳烃化合物芘、六苯并苯、红荧烯作为研究对象,考察了这3种化合物激光电离产物的差异,并研究了激光能量对六苯并苯产物离子分布的影响.结果表明,观察到芘、六苯并苯多聚体离子产物,还观测到了六苯并苯失去C2H2的碎片离子峰;而没有观测到明显的红荧烯聚合物离子产物,只观测到了大量失去C6H5的碎片离子峰.最后,对3种不同化合物的激光电离微观机理进行了分析.由于芘、六苯并苯具有平面大π键,分子间的π-π键相互作用是产生多聚体离子的主要原因;而红荧烯的空间位阻削弱了分子间相互作用,从而阻碍了多聚体离子的形成.     

Determination of Dimethyl Sulfide in Gas Samples by Single Photon Ionization Time of Flight Mass Spectrometry

It is difficult to determine sulfur-containing volatile organic compounds in the atmosphere because of their reactivity. Primary off-line techniques may suffer losses of analytes during the transportation from field to laboratory and sample preparation. In this study, a novel method was developed to directly measure dimethyl sulfide at parts-per-billion concentration levels in the atmosphere using vacuum ultraviolet single photon ionization time-of-flight mass spectrometry. This technique offers continuous sampling at a response rate of one measurement per second, or cumulative measurements over longer time periods. Laboratory prepared samples of different concentrations of dimethyl sulfide in pure nitrogen gas were analyzed at several sampling frequencies. Good precision was achieved using sampling periods of at least 60 seconds with a relative standard deviation of less than 25%. The detection limit for dimethyl sulfide was below the 3 ppb olfactory threshold. These results demonstrate that single photon ionization time-of-flight mass spectrometry is a valuable tool for rapid, real-time measurements of sulfur-containing organic compounds in the air.     

激光溅射金属等离子体与醇类分子束反应的研究：产物离子对分子束状态的依赖性

The gas phase reactions of metal plasma with alcohol clusters were studied by time of flight mass spectrometry （TOFMS） using laser ablation-molecular beam （LAMB） method. The significant dependence of the product cluster ions on the molecular beam conditions was observed. When the plasma acted on the low density parts of the pulsed molecular beam, the metal-alcohol complexes M^＋An （M=Cu, Al, Mg, Ni and A=C2H5OH, CH3OH） were the dominant products, and the sizes of product ion clusters were smaller. While the plasma acted on the high density part of the beam, however, the main products turned to be protonated alcohol clusters H^＋An and, as the reactions of plasma with methanol were concerned, the protonated water-methanol complexes H3O^＋（CH3OH）n with a larger size （n≤12 for ethanol and n≤24 for methanol）. Similarly, as the pressure of the carrier helium gas was varied from 1 × 10^5 to 5 × 10^5 Pa, the main products were changed from M^＋An to H^＋An and the sizes of the clusters also increased. The changes in the product clusters were attributed to the different formation mechanism of the output ions, that is, the M^＋An ions came from the reaction of metal ion with alcohol clusters, while H^＋An mainly from collisional reaction of electron with alcohol clusters.     

Ejection of Cluster Ions from a Liquid Beam of an Aniline-Propanol Solution Following Laser Photoionization

A simple technique of preparing a continuous laminar liquid flow in vacuum (liquid beam) was developed and combined with multiphoton ionization and a time-of-flight mass spectrometer. This technique was applied to the study on resonance photoionization of an aniline (AN)-propanol (PrOH) solution (0.1 – 0.3 M). Binary cluster ions of aniline and propanol, AN⁺(PrOH)_n (n ≤ 1), and protonated propanol cluster ions, H⁺(PrOH)_n (n ≤ 1), were observed as product ions in the gas phase. The relative intensities of AN⁺PrOH and those of H⁺(PrOH)₂ were measured as functions of the excitation laser power and the concentration of aniline in the propanol solution. The dependences of the ion intensities on the laser power and the AN concentration are explained in terms of a Coulomb ejection model, where the ions are ejected from the surface by Coulomb repulsion exerted from neighboring ions. It is also concluded that H⁺(PrOH)_n is produced by a proton transfer reaction from an aniline ion to solvent molecules in the solution.