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1.
采用超声分子束技术,以飞行时间质谱仪,在410~371nm内着重检测了不同波长、不同能量的激光对气相Si(CH3)4分子多光子电离(MPI)飞行时间(TOF)质谱产物分布的影响。根据实验结果,对Si(CH3)4分子多光子解离电离可能经历的通道和反应机理进行了讨论。 相似文献
2.
We succeeded in depositing nanometric Zn dots using near-field optical chemical vapor deposition (NFO-CVD). Conventional optical
CVD is based on an adiabatic photochemical process and requires UV light to excite molecules from the ground electronic state
to the excited state for dissociation. By contrast, in near-field optical CVD (NFO-CVD), non-adiabatic photodissociation takes
place, even with visible light, as a consequence of the steep spatial gradient of the optical power of an optical near field.
This non-adiabatic process, which can be explained using the exciton–phonon polariton model, enables the photodissociation
of optically inactive Zn(acac)2. We discuss experimental results using the exciton–phonon polariton model.
PACS 33.80.Gj; 82.50.-m; 81.16.Be 相似文献
3.
大气臭氧层因吸收太阳紫外光, 是人类必不可少的保护伞. 氟利昂在太阳光辐射下解离生成破坏臭氧的游离态氯原子, 是破坏大气臭氧层的主要元凶之一. 本文利用飞行时间质谱技术和离子速度成像技术研究了氟利昂F113(三氟三氯乙烷)分子在800 nm 飞秒光作用下的多光子电离解离动力学. 利用飞行时间质谱探测技术, 得到了三氟三氯乙烷在该波长飞秒激光作用下发生多光子电离解离产生的碎片质谱. 通过荷质比对碎片质谱进行了详细的标定和分析. 在质谱上未发现母体离子, 所有观察到的离子都是由于激光脉冲作用下产生的碎片. 三个最主要的碎片离子是CFCl2+, CF2Cl+, C2F3Cl2+. 通过飞行时间质谱标定, 发现并归属了多个解离通道. 三个主要的解离机理分别为: 1) C-Cl键断裂直接生产氯自由基的通道C2F3Cl3+→C2F3Cl2++Cl; 2) C--C键断裂C2F3Cl3+→CFCl2++CF2Cl; 3) C--C键断裂C2F3Cl3+→CF2Cl++CFCl2. 利用离子速度成像技术对这三个主要通道产生的碎片离子进行成像, 得到了C2F3Cl2+, CFCl2+和CF2Cl+离子的速度影像. 由C--Cl键断裂产生的碎片离子C2F3Cl2^{+}的速度分布由两个高斯分布曲线拟合, 而由C--C键断裂产生的碎片离子CFCl2+和CF2Cl+可以用一个高斯曲线拟合. 通过影像分析得到了解离碎片的平动能分布和角向分布各向异性参数等详尽的动力学信息. 结合高精度密度泛函理论计算对解离动力学进行了进一步的分析和讨论.深入认识氟利昂的解离动力学可为进一步控制破坏臭氧层提供理论参考和实验依据. 相似文献
4.
采用密度泛函和耦合簇理论从过渡态的观点对CH_3I~(2+)离子的解离过程进行了计算和分析.优化得到了CH_3I,CH_3I+和CH_3I~(2+)的稳定结构及解离过渡态的几何构型并给出了相应能量,计算的第一、二电离能与实验结果符合.基于母体离子、过渡态和解离碎片的几何结构和能量,对CH_3I~(2+)的两体解离过程和三体解离过程进行了详细分析和讨论.给出了二体、三体解离的可能解离通道,并分析了实验上观测到的解离碎片离子的产生机制.计算结果表明,三重和单重绝热势能面上的一些解离过程表现出明显的差异. 相似文献
5.
Photofragmentation of Na2 + molecules in well prepared vibrational levels has been studied employing intense ( 10(11)-10(14) W/cm2) and ultrashort (80 fs) 790 nm laser fields. Four fragmentation channels with different released kinetic energies are observed. Depending on the applied laser intensity, the fragmentation of Na2 + is governed by photodissociation on light-induced potentials and field ionization followed by Coulomb explosion. Below 1x10(12) W/cm2, only photodissociation on light-induced potentials is seen. For intermediate laser intensities, field ionization at large internuclear distances competes with photodissociation, thus preventing the observation of above threshold dissociation. Field ionization at small internuclear distances dominates for the highest laser intensities used. 相似文献
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用多光子电离技术结合飞行时间质谱仪对氨与乙醇混合团簇进行了研究。在脉冲激光波长分别为266,355nm和532nm条件下,仅在355nm作用下观测到团簇离子。主要的电离产物为质子化的(C2H5OH)n(NH3)mH+(n=0—3,m=0—4)混合团簇离子,且各个序列的离子强度随m的增大而减小。经分析,氨与乙醇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。通过理论计算得到其中性和离子团簇的稳定结构,解离能,解离通道。并证实团簇发生电离解离时发生了团簇内质子转移反应。 相似文献
8.
OK Yoon WG Hwang JC Choe MS Kim 《Rapid communications in mass spectrometry : RCM》1999,13(14):1515-1521
A technique to investigate photodissociation kinetics on a nanosecond time scale has been devised for molecular ions generated by multiphoton ionization (MPI) using mass-analyzed ion kinetic energy spectrometry. The branching ratio or rate constant has been determined for the photodissociation of the n-butylbenzene, bromobenzene, iodobenzene, and aniline molecular ions generated by MPI at 266 nm. The ion internal energies have been estimated by comparing the measured kinetic data with the previous energy dependence data. The analysis has shown that only those molecular ions generated by two-photon ionization contribute to the photodissociation signals. Around half of the available energy has been found to remain as molecular ion internal energy in the two-photon ionization process. Copyright 1999 John Wiley & Sons, Ltd. 相似文献
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F. Assenmacher M. Gutmann F. Noack V. Stert W. Radloff 《Applied physics. B, Lasers and optics》2000,71(3):385-390
The photodissociation dynamics of HNO3 in the electronic S3 (2 1
A
′
) state leading to the fragments OH and NO2 was investigated in real time. HNO3 was prepared either in a fluorescence cell at room temperature (LIF probing of OH) or rotationally cold in a molecular beam
(probing of NO2 by three-photon ionization). A 2 1
A
′
lifetime of 60–80 fs could be obtained from the experimental results, indicating essentially barrierless dissociation. In
addition, secondary dissociation of internally excited nascent fragments NO2
* leading to products NO(X 2
Π) and O(3
P) with a characteristic dissociation time of 2.3 ps was observed. This time is surprisingly long when compared with dissociation
lifetimes of NO2 from the literature, obtained after direct photoexcitation. The discrepancy is explained by differences in the preparation
conditions of the dissociative state of NO2.
Received: 12 November 1999 / Published online: 13 July 2000 相似文献
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Sann H Jahnke T Havermeier T Kreidi K Stuck C Meckel M Schöffler MS Neumann N Wallauer R Voss S Czasch A Jagutzki O Weber T Schmidt-Böcking H Miyabe S Haxton DJ Orel AE Rescigno TN Dörner R 《Physical review letters》2011,106(13):133001
We doubly ionize H(2)O by single photon absorption at 43 eV leading to H(+) + OH(+). A direct double ionization and a sequential process in which single ionization is followed by rapid dissociation into a proton and an autoionizing OH(*) are identified. The angular distribution of this delayed autoionization electron shows a preferred emission in the direction of the emitted proton. From this diffraction feature we obtain internuclear distances of 700 to 1100 a.u. at which the autoionization of the OH(*) occurs. The experimental findings are in line with calculations of the excited potential energy surfaces and their lifetimes. 相似文献
13.
卤代烷烃会破坏臭氧层,而碘乙烷(C2H5I)是卤代烷烃中重要代表物质之一.采用离子速度成像技术、飞秒激光技术和飞行时间质谱技术,探究了C2H5I的多光子电离解离动力学.通过分析C2H5I在强场作用下多光子电离解离得到的解离通道、碎片的动能、角度分布和各向异性参数等信息来研究碘乙烷离子(C2H5I+)C–I键裂解机理.根据飞行时间质谱实验,C2H5I在飞秒激光脉冲作用下发生多光子电离解离得到的碎片有C2H5+,I+,CH2I+,C2H2+,C2H3+,C2H4+等.与C–I键相关的碎片为C2H5+和I+,解离机制分别对应于C2H5I+→C2H5++I和C2H5I+→C2H5+I+.同时,采用离子速度成像技术研究C2H5I+的C–I键裂解产生的C2H5+和I+的速度影像,得出两者的速度分布和动能分布,分析结果表明C–I键裂解产生C2H5+和I+的过程都存在高能通道和低能通道.进一步分析解离碎片离子的角度分布发现C2H5+解离时各向异性参数接近于0,可能对应于慢速的振动预解离过程.I+在解离时各向异性参数较高,可能源于排斥势能面上的快速解离过程.最后采用密度泛函理论计算了C2H5I分子电离前后构型变化、离子态的能级强度及谐振强度,对C2H5I+的解离机制做了更进一步的分析和讨论. 相似文献
14.
W. Cui Y. Hu C. Lifshitz 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2002,20(3):565-571
A new instrument has been constructed whose purpose is to study time-resolved photodissociation (TRPD) of small peptide ions.
Laser desorption of neutral peptides is combined with laser photoionization in an ion trap followed by thermalization, laser
photodissociation and time of flight mass analysis. Ionization and excitation take place through an aromatic chromophore at
the C-terminus of the peptide whereas dissociation produces the immonium ion at the N-terminus. The long-range purpose is
to uncover the role of IVR in unimolecular fragmentations of peptide radical cations. One avenue is the determination of microcanonical
rate constants at a well-defined internal energy E for a series of peptides possessing the same chromophore, undergoing the same fragmentation but having a variable number
of degrees of freedom. This paper demonstrates the feasibility of the method and provides the first attempts at rate measurements
for the peptide leucyl tyrosine (LeuTyr).
Received 6 January 2002 Published online 13 September 2002 相似文献
15.
利用里德堡氢原子飞渡时间谱的方法,进行了甲基自由基在212.5nm 的光解动力学的实验研究.甲基自由基来自于碘甲烷分子在266nm 的光分解.实验测量了不同振动态的甲基自由基通过3s 电子激发态解离的产物 CH_2自由基的平动能分布和角分布,并从平动能分布得到了 CH_2自由基的转动布居.实验同时详细地研究了母体分子甲基自由基的振动和转动激发对光解动力学的影响.实验结果表明母体分乙甲基自由基的伞形振动对于产物的转动激发和角分布均有较大的影响,而母体分子的转动激发只对产物的角分布有较明显的影响. 相似文献
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Fryčák P Jirkovský J Ranc V Bednář P Havlíček V Lemr K 《Journal of mass spectrometry : JMS》2012,47(6):720-726
Atmospheric pressure chemical ionization is known for producing unusual artifacts of the ionization process in some cases. In this work, processes occuring in atmospheric pressure chemical ionization/MS of orotic acid that afforded ions accompanying protonated and deprotonated orotic acid molecules in the spectra were studied. Two processes ran in parallel in the ion source: decarboxylation of neutral orotic acid and collision-induced dissociation of its protonated or deprotonated form. A procedure discerning pre-ionization decomposition and post-ionization dissociation by manipulating ion source parameters was proposed. Experiments with isotopically labeled solvents confirmed ion-molecule reactions of the product of collision-induced dissociation of protonated orotic acid with solvent molecules in the ion source and even under vacuum in the ion trap. 相似文献
18.
K. O. Korovin E. Heinecke A. Patzer T. Liebig O. S. Vasyutinskii D. Zimmermann 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2007,44(1):57-63
The first determination of translational anisotropy parameters β in the
photodissociation of NaI molecules in the spectral range
315–370 nm is reported. The anisotropy parameters were
determined by the analysis of Doppler resolved absorption profiles of
Na(2S1/2) atoms produced in the photodissociation of NaI by
linearly polarized light. The profiles were recorded for two orientations of
the photolysis light: parallel and perpendicular to the direction of the
probe beam. The value of the parameter β was obtained from a simultaneous fit
of the profiles. The role of the rotation of the parent molecules on the
branching ratio between parallel and perpendicular transitions in NaI during
dissociation is discussed. 相似文献
19.
The nascent translational energy distributions of group 13 metal ions produced via multiphoton dissociation and multiphoton ionization (MPD/MPI) of their trimethyl derivatives and via multiphoton ionization of metal atomic beams have been measured using time-of-flight mass-spectroscopy. In all cases the ion production was isotropic and the translational energy distribution was approximately Boltzmann. For ionization of free aluminum and indium atoms translational temperatures of 6K and 4K were measured, corresponding to most probable velocities of 60 and 24 ms–1. From multiphoton dissociation of trimethylaluminum, trimethylgallium, and trimethylindium, translational temperatures of 1800, 700, and 900 K resulted. These correspond to velocities of 1000, 400, and 350 ms–1. A photodissociation mechanism involving elimination of ethane followed by dissociation of monomethyl metal intermediates to produce metal atoms is in reasonable agreement with the experimental data. The nascent velocities of metal atoms and ions from the metal alkyl and metal beam sources are used to assess the potential of these sources for microfabrication of metal structures. 相似文献
20.
M-shell ionization cross sections for atoms due to the impact of proton and α-particles have been calculated in the binary
encounter approximation. The effects of Coulomb deflection of the incident projectile and increase in binding of the target
electron have been investigated. Roothan-Hartree-Fock velocity distribution for the target electrons has been used in the
present work. The calculated cross-sections have been compared with experimental results and other theoretical calculations
wherever available. The present calculations give a good account of experimental observations. 相似文献