532nm丙酮和丁酮的多光子电离解离研究

利用激光质谱法,通过分析丙酮和丁酮的多光子电离飞行时间质谱,对其532 nm多光子电离机制进行了研究.结果发现丙酮相干吸收若干光子跃迁到高能超激发态,再继续吸收光子产生各种碎片离子,而丁酮先解离后电离,两质谱中都有质荷比为4、6、8的离子,原则上是高价离子.但在相似条件下未见相关报道,因此对离子出险原因及确认尚待进一步研究,实验中丁酮发生异构现象,其异构体电离解离出较强的C2H3O (m/e=43).丙酮没有相关离子产生.     

532nm丙酮和丁酮多光子电离解离研究

利用激光质谱法,通过分析丙酮和丁酮的多光子电离飞行时间质谱,对其532nm多光子电离机制进行了研究. 结果发现丙酮相干吸收若干光子跃迁到高能超激发态,再继续吸收光子产生各种碎片离子,而丁酮先解离后电离. 两质谱中都有质荷比为4、6、8的离子,原则上是高价离子,但在相似条件下未见相关报道,因此对离子出险原因及确认尚待进一步研究. 实验中丁酮发生异构现象,其异构体电离解离出较强的C2H3O+(m/e=43).丙酮没有相关离子产生.     

532nm及355nm丁酮多光子电离质谱研究

利用激光质谱法,采用355 nm及532 nm激光作为光源对丁酮分子进行了多光子电离解离研究,得到了2种波长下丁酮的多光子电离飞行时间质谱图主要有质荷比为1(H ),15(CH3 ),43(CH3CO )的质谱峰.532 nm质谱比较丰富,有较强的质荷比为45的信号,可以认为这是丁酮异构体电离解离得到的产物;同时探测到了质荷比为4,6,8的信号,可能是高价离子.355 nm质谱图相对简单.根据信号比例随激光能量的变化及主要的离子信号,得出了2种波长下主要的解离电离通道.     

532 nm及355 nm丁酮多光子电离质谱研究

利用激光质谱法,采用355 nm及532 nm激光作为光源对丁酮分子进行了多光子电离解离研究,得到了2种波长下丁酮的多光子电离飞行时间质谱图主要有质荷比为1(H ),15(CH3 ),43(CH3CO )的质谱峰.532 nm质谱比较丰富,有较强的质荷比为45的信号,可以认为这是丁酮异构体电离解离得到的产物;同时探测到了质荷比为4,6,8的信号,可能是高价离子.355 nm质谱图相对简单.根据信号比例随激光能量的变化及主要的离子信号,得出了2种波长下主要的解离电离通道.     

甲醇－乙醚团簇的多光子电离和从头算

在355 nm波长下用激光电离飞行时间质谱装置研究了氢键团簇甲醇/乙醚混合团簇的多光子电离,飞行时间质谱仪观测到一系列质子化团簇,为了探讨质子化团簇的形成机理,在B3LYP/6-31 G(d,p)//B3LYP/6-311 G(d,p)基组水平上计算了CH30H-(C2H5)2O离子和中性团簇的稳定几何结构和解离通道和解离能,发现存在一个质子转移过程,解离产物主要为CH3O和[(C2H5)2O]H .     

355_nm激光下邻氯苯酚-水团簇的多光子电离与从头计算研究

应用激光多光子电离质谱与超声脉冲分子束技术研究邻氯苯酚-水的混合团簇。实验中观测到C6H5ClO-(H2O)m+（m=1,2,…,5）团簇系列,通过对其质谱图的分析,得到产生该团簇的电离解离通道;用Gaussian03计算程序在B3LYP/6-31G基组水平上对部分团簇离子的可能构型进行优化,获得稳定构型。     

应用反射式飞行时间质谱仪研究氨团簇离子解离动力学

用直射式和反射式飞行时间质谱研究了氨分子团簇体系在３５５ｎｍ激光下的多光子电离,得到一系列的质子化团簇离子（ＮＨ３）ｎＨ＾＋,同时还观察到超价氨团簇离子（ＮＨ３）ｎＨ＾＋２。在反射式飞行时间质谱研究中观测到质子化氨团簇离子在自由飞行过程中的解离现象,表明在该实验条件下生成的质子化氨团簇离子是一些亚稳态团簇离子。对子离子产率的分析,得到质子化团簇离子解离速率常数,从而可以估计亚稳态团簇离子的寿命。团     

氨团簇（NH3）n的多光子电离质谱研究

在355nm激光作用下,对氨团簇的多光子电离过程进行了研究,发现电离过程中出现了氢团簇离子序列(NH3) n(n=2-6)和氨质子化团簇离子序列(NH3)nH (n=2-15).分析认为在氨团簇的多光子电离过程中仅可能是由于氨团簇在激光作用下遵循了AID机制.而对于实验中出现的氨质子化团簇离子序列,目前实验上的困难暂不能确定其产生的具体途径.     

乙腈和氨水团簇的激光电离实验研究

在355nm激光波长下应用多光子电离和分子束技术研究了乙腈和氨水的混合团簇,所得的团簇离子以(CH3CN) n、(CH3CN)nNH 3和(CH3CN)n(NH3) 为主,中性团簇以二元团簇(CH3CN)n(NH3)m/(CH3CN)n(NH4OH)m为主.离子产物是来源于中性的二元团簇先吸收部分激光能量解离成稳定的小团簇和碎片,然后再发生分子蒸发和电离的过程,并未发生明显的质子转移反应.     

甲醇/水混合团簇的多光子电离质谱研究

利用多光子电离技术结合飞行时间质谱仪对甲醇/水混合团簇进行了研究.在脉冲激光波长为355 nm条件下观测到团簇离子.主要的电离产物为质子化的(CH3OH)n(H2O)H+(n=l-13)混合团簇离子与(CH3OH)nH+团簇离子,经分析(CH3OH)1o(H2O) H+和(CH3OH)3H+为幻数结构.甲醇水混合团簇电离后团簇离子发生内部质子化转移反应是形成质子化团簇离子的主要原因.不同尺寸团簇离子信号强度随电离激光光强变化的光强指数曲线显示,团簇均发生四光子电离过程.     

Cluster Structure of Liquid Alcohols,Water, and <Emphasis Type="Italic">n</Emphasis>-Hexane

The processes of cluster formation in liquid alcohols, water, methanol, n-hexanol, and n-hexane have been investigated by the method of flicker-noise spectroscopy. Two types of clusters — clusters with a close-packed structure and clusters with a loose structure — have been detected. The energy of formation of different clusters in methanol and n-hexane ranges, respectively, from −250 to +250 J/mole and from −50 to +50 J/mole. The smallest clusters of methanol, n-hexanol, water, and n-hexane consist, respectively, of six, two, eleven, and two molecules, and their largest clusters represent oscillators consisting, respectively, of 50,400, 17,200, 93,500, and 33,150 molecules at 274 K. In methanol at 271 K, more than 44 types of clusters consisting of 6, 97, 152, 219, 297, 492, 1029, 1368, 1560, etc. molecules were detected. In n-hexanol at 273 K, 57 types of clusters were detected. Models of small clusters are proposed. In water, the content of close-packed clusters is maximum at 277 K. The energy of formation/decomposition of small clusters in water ranges from −0.4 to +0.4 kJ/mole and increases with increase in the water temperature. The hysteresis of transformation of the (H₂O)₂₈₀ cluster in the process of heating and cooling of water in the temperature range 273–280 K was detected. Series of energy spectra of clusters in liquids at different temperatures are presented and discussed. __________ Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 72, No. 3, pp. 305–312, May–June, 2005.     

氢化非晶硅薄膜退火形成的纳米硅及其光致发光

本文报道对氢化非晶硅(a-Si:H)薄膜在600～620℃温度下快速退火10s可以形成纳米晶硅(nc-Si),其Raman散射表明,在所形成的nc-Si在薄膜中的分布是随机的,直径在1.6～15nm范围内,并且在强激光辐照下观察了nc-Si在薄膜中的结晶和生长情况.经退火所形成的nc-Si可见光辐射较弱,不能检测到它们的光致发光(PL),但用氢氟酸腐蚀钝化后则可检测到较强的红PL,并且钝化后的nc-Si在空气中暴露一定的时间后,其辐射光波长产生了蓝移.文中就表面钝化和量子限制对可见光辐射的重要性作了讨论.     

Fabrication and characterization of SERS‐active silver clusters on glassy carbon

In this article, a novel technique for the fabrication of surface enhanced Raman scattering (SERS) active silver clusters on glassy carbon (GC) has been proposed. It was found that silver clusters could be formed on a layer of positively charged poly(diallyldimethylammonium) (PDDA) anchored to a carbon surface by 4‐aminobenzoic acid when a drop containing silver nanoparticles was deposited on it. The characteristics of the obtained silver clusters have been investigated by atomic force microscopy (AFM), SERS and an SERS‐based Raman mapping technique in the form of line scanning. The AFM image shows that the silver clusters consist of several silver nanoparticles and the size of the clusters is in the range 80–100 nm. The SERS spectra of different concentrations of rhodamine 6G (R6G) on the silver clusters were obtained and compared with those from a silver colloid. The apparent enhancement factor (AEF) was estimated to be as large as 3.1 × 10⁴ relative to silver colloid, which might have resulted from the presence of ‘hot‐spots’ at the silver clusters, providing a highly localized electromagnetic field for the large enhancement of the SERS spectra of R6G. The minimum electromagnetic enhancement factor (EEF) is estimated to be 5.4 × 10⁷ by comparison with the SERS spectra of R6G on the silver clusters and on the bare GC surface. SERS‐based Raman mapping technique in the form of line scanning further illustrates the good SERS activity and reproducibility on the silver clusters. Finally, 4‐mercaptopyridine (4‐Mpy) was chosen as an analyte and the lowest detected concentration was investigated by the SERS‐active silver clusters. A concentration of 1.6 × 10⁻¹⁰ M 4‐Mpy could be detected with the SERS‐active silver clusters, showing the great potential of the technique in practical applications of microanalysis with high sensitivity. Copyright © 2006 John Wiley & Sons, Ltd.     

Structure determination of gas-phase niobium and tantalum carbide nanocrystals via infrared spectroscopy

Niobium and tantalum carbide clusters have been isolated in the gas phase and irradiated with intense tunable infrared (IR) light. Stable neutral clusters are selectively ionized and subsequently detected in a mass spectrometer. By tuning the IR frequency, infrared multiphoton absorption spectra are obtained for a whole range of clusters. These mass-selective IR spectra lead to insights into the structures of small niobium and tantalum carbide clusters and nanocrystals.     

The ionization potentials of clustered sodium atoms

Small clusters of sodium atoms have been produced by the isentropic flow of high pressure vapour through a small orifice. These clusters have been ionized by ultra-violet light and detected using a mass spectrometer. Clusters of up to eight sodium atoms have been observed and their ionization potentials have been measured. The ionization potentials of Na₃ and Na_s are 3.9 v and 4.0 v respectively, showing that even the smallest clusters tend to the value expected for a continuous drop of metal of the same size.     

Optical switching in a Ξ system: A comparative study on DROP and EIT

Liquid Lennard-Jones clusters with magic number of atoms N = 55, 147, 309, 561 and 923 were cooled down in Monte Carlo simulations until freezing. Structural properties of the clusters, including the radial dependence of atomic concentration/density and the local regular structure in arrangement of atoms, just before freezing were analysed. Existence of spherical layers in atomic density around the centre of mass of liquid LJ clusters was confirmed. Formation of layers is explained by central net forces acting on every cluster atom and leading to positioning an atom close to the cluster centre of mass. The strong layering in small clusters of N = 55 and 147 affects atomic diffusion in radial and tangential directions inside the cluster, leading to easier movement of atoms on the layer surface. Analysis of radial profiles of four types of structural units detected in liquid clusters reveals that icosahedral units are the most numerous and are located mainly near cluster surface of all clusters and also in the centre of small clusters.     

A Photoionization TOF Mass Spectrometric Investigation on Neutral Aluminum Clusters

IntensiveinvestigationshavebeenPerformedonaluminumclustersrecently,mainlyinattemptstotestanddevelopideasaboutmetalclusters,aconcentrativetopicofwhichistotestthevalidityoftheelectronicshel]modelsforaluminumclusters.Intheelectronicshellmodels,metalclustersaresimplifiedasvalenceelectronsmovingaroundasphericalorspheroidalpositively--chargedbackground,wherethevalenceelectronswithinaclusteraredelocalizedandthedetailedatomicconfigurationplayaminorrole.Suchsimplifiedmodelscanexplainmostofthediscontinu…     

Charge localization in collision-induced multiple ionization of van der Waals clusters with highly charged ions

Charge localization in multiple ionization and fragmentation of small argon clusters is reported. The processes are initiated by interaction of the neutral cluster with highly charged Xe(q+) (5< or =q< or =25). Products are detected by means of multicoincidence time-of-flight methods. A strong dependence of the fragmentation pattern on the Xe charge state q is observed. In particular, we find evidence for formation of multiply charged atomic Ar(r+) fragment ions up to r = 7. Such high charge states have neither been observed in fission of multiply charged van der Waals clusters nor in ion-induced fragmentation of fullerenes or metal clusters. This hints at fundamentally different excitation and fragmentation dynamics.     

Local atomic structures of amorphous Pd80Si20 alloys and their configuration heredity in the rapid solidification

The local atomic structures of amorphous Pd₈₀Si₂₀ alloys and their configuration heredity in the rapid solidification are investigated by a molecular dynamics simulation with the help of cluster-type index method based on Honeycutt–Anderson bond-type index and an inversely tracking technique of atomic trajectories. Their short-range orders are found to be various Kasper clusters as well as their distorted configurations, and among which (10 2/1441 8/1551) bi-capped square Archimedean anti-prism (BSAP) clusters are dominated, e.g. Si-centred Pd₁₀Si₁ clusters. These Kasper clusters mainly exist in the form of isolated basic clusters. Few medium-range orders can be detected, especially for Si-centred Kasper clusters. Similarly to icosahedrons of Cu–Zr amorphous alloys, their sustainable configuration heredity also occurs firstly in the super-cooled liquid region, and BSAP clusters have higher onset temperature T_onset and bigger descendible fraction F than other Kasper clusters in the rapid solidification of Pd₈₀Si₂₀ alloys.     

Vibrational spectroscopy of large water clusters of known size

The structure of large water clusters of known size distributions 〈n〉 = 20-2000 is investigated by vibrational spectroscopy of the OH stretch mode. The water clusters are predissociated by a pulsed tunable infrared optical parametrical oscillator (OPO) in the frequency range 2800-3800 cm^-1. Their fragments are detected off-axis by electron impact ionization and mass analyzed by a quadrupole mass spectrometer. The largest ion signal stems from the neutral water hexamer fragment. The ion yield is investigated at certain wavelengths while the size of the clusters is varied, and for certain sizes complete absorption spectra of the OH stretch motion are measured. Fingerprints of the different coordination types of the water molecules in the clusters are found and it turns out that our method is especially sensitive to amorphous structures with frequencies shifting in the range of 3300-3400 cm^-1.