Differentiation of Positional Isomers of Propyl Alcohols Using Filament-Induced Fluorescence

We experimentally demonstrate the recognition of positional isomers of propyl alcohol vapor through nonlinear fluorescence induced by high-intensity femtosecond laser filaments in air.By measuring characteristic fluorescence of n-propyl and isopropyl alcohol vapors produced by femtosecond filament excitation,it is found that they show identical spectra,that is,those from molecular bands of CH,C_2,NH,OH and CN,while the relative intensities are different.By comparing the ratios of the CH and C_2 signals,the two propyl alcohol isomers are differentiated.The different signal intensities are ascribed to different ionization potentials of the two isomer molecules,leading to different production efficiencies of fluorescing fragments.     

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.     

瓦斯浓度影响下水合物晶体结构Raman光谱特征

在初始温压2 ℃,5 MPa条件下开展了三种瓦斯混合气(CH₄—C₂H₆—N₂,G1=54∶36∶10,G2=67.5∶22.5∶10,G3=81∶9∶10)水合实验,利用可见显微拉曼光谱仪获取水合产物拉曼光谱,通过水合物相中C₂H₆ C—C键伸缩振动特征峰拉曼位移判断水合物晶体结构,利用谱图特征峰分峰拟合方法计算出瓦斯水合物孔穴占有率、水合指数等。研究发现：气样G1和G2水合产物为I型水合物、G3为Ⅱ型,气样中C₂H₆浓度改变导致水合物晶体结构转变;Ⅰ型结构水合物相中CH₄和C₂H₆含量受气样浓度影响较小,G1和G2体系中CH₄含量分别为34.4%和35.7%、C₂H₆含量分别为64.6%和63.9%,而G3体系中CH₄和C₂H₆含量分别为73.5%和22.8%,晶体结构对水合物相客体分子含量控制作用明显;G1~G3体系水合物相大孔穴的CH₄—C₂H₆占有率分别为98%,98%和92%,小孔穴的CH₄占有率分别为80%,60%和84%,N₂由于分压较低且吸附能力较弱其小孔穴占有率不高于5%。     

电荷调控下Ti3C2O2和V2CO2吸附CH4的第一性原理计算

本文采用第一性原理计算首先研究了Ti3C2O2和V2CO2与CH4气体分子之间的相互作用,发现Ti3C2O2和V2CO2对CH4的吸附较弱属于物理吸附,不适宜用作探测CH4。在此基础上研究了电荷调控下CH4气体分子与Ti3C2O2和V2CO2之间的相互作用。结果表明：随着体系电荷态的增加,Ti3C2O2和V2CO2对CH4气体分子的吸附作用逐渐增加变为化学吸附。当体系电荷态大于或等于-2时,CH4气体分子在Ti3C2O2和V2CO2表面可以被有效捕获。撤去电荷后,Ti3C2O2、V2CO2与CH4气体分子之间的吸附恢复至物理吸附,CH4气体分子易脱附。因此,通过调控Ti3C2O2和V2CO2的电荷态,可以简单地实现CH4的捕获与释放。Ti3C2O2和V2CO2有望成为CH4探测或捕获材料。     

时间分辨红外发射光谱法对自由基反应的研究

在过去的 15年中 ,傅立叶变换红外发射光谱法广泛应用于研究气相自由基反应 .Sloan首先研究了O(1D)的反应 ,随后Leone和Hancock研究了O(3 P)的反应 .此后 ,孔繁敖和朱起鹤等研究了小自由基 ,包括CH、CH2 、CH3 、C2 H3 、C2 H5、C2 H、C3 H3 和C3 H5与O2 、NO、N2 O、NO2 等分子的反应。在红外光谱中观察到各个反应的初生产物和初步反应通道 ,和从头算的理论研究结合起来 ,这些反应的机理已基本弄清 .     

Surface diffusion: the low activation energy path for nanotube growth

We present the temperature dependence of the growth rate of carbon nanofibers by plasma-enhanced chemical vapor deposition with Ni, Co, and Fe catalysts. We extrapolate a common low activation energy of 0.23-0.4 eV, much lower than for thermal deposition. The carbon diffusion on the catalyst surface and the stability of the precursor molecules, C2H2 or CH4, are investigated by ab initio plane wave density functional calculations. We find a low activation energy of 0.4 eV for carbon surface diffusion on Ni and Co (111) planes, much lower than for bulk diffusion. The energy barrier for C2H2 and CH4 dissociation is at least 1.3 eV and 0.9 eV, respectively, on Ni(111) planes or step edges. Hence, the rate-limiting step for plasma-enhanced growth is carbon diffusion on the catalyst surface, while an extra barrier is present for thermal growth due to gas decomposition.     

Observation of accurate ion dissociation thresholds in pulsed field ionization-photoelectron studies

We report the first observation, together with a mechanism for such an observation, of a steplike feature in the pulsed field ionization photoelectron measurement of CH4(C2H2), marking the 0 K dissociation threshold for the formation of CH3(+) + H(C2H(+) + H) from CH4(C2H2). The nonexistence of a step in the spectrum for C 2H4 at its dissociation threshold for C2H2(+) formation provides strong support for the proposed mechanism. This experiment shows that, for a range of molecules, where the ion dissociation lifetimes near the dissociation thresholds are <10(-7) s, pulsed field ionization photoelectron measurements will yield not only highly accurate ionization energies, but also 0 K dissociation thresholds.     

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 .     

Cavity ring-down spectroscopy of CH and CD radicals in a diamond thin film chemical vapor deposition reactor

A mixture of H₂ and CH₄ is passed over a hot-wire tungsten filament in a diamond thin film chemical vapor deposition reactor. The resulting CH radicals are measured in absorption using cavity ring-down spectroscopy (CRDS). The concentration of the CH radicals increases as the filament is approached. The rotational temperature measurements indicate a large temperature discontinuity between the filament and the CH in the gas phase. The pathways for CH production were investigated by replacing H₂ by D₂ in the feed gas mixture, which resulted in the exclusive production of CD. From this observation it is concluded that rapid H/D isotope exchange dominates in the gas phase. Nonperiodic temporal oscillations in the CH concentration are observed when a rhenium filament is used in place of a tungsten filament. The oscillations are attributed to the nonperiodic changes in the amount of carbon at the filament surface. Received: 21 August 2000 / Accepted: 23 August 2000 / Published online: 23 May 2001     

射频辉光放电CH4等离子体一维流体动力学模拟

完整建立一个关于射频辉光放电CH₄等离子体的流体动力学模型.模型包括基于迁移-扩散近似的粒子平衡方程、电子能量平衡方程,共包含了20种粒子(环境气体粒子,激发态粒子,离子和电子)和49类化学反应(电子-中性环境粒子、离子-中性环境粒子、激发态粒子-激发态粒子(中性环境粒子)).结果表明,在强电场区域有较高的电子反应率系数;等离子体中除源气体CH₄外,H₂,C₂H₆,C₃H₈,C₂H₄和C₂H₂也有较高的密度含量;激发态粒子中,CH₃含量最高,密度约为10¹⁹m^-3;在较低放电压力时(如18 Pa),CH₅⁺在离子成分中密度含量最高,当放电压力较高时(如67Pa),C₂H₅⁺在离子成分中占主导地位;除C₂H₅⁺外,其它各离子和激发态粒子在极板上的粒子流量随功率的增大逐渐升高.     

Berry-phase calculation of magnetic screening and rotational g factor in molecules and solids

The orbital magnetic moment due to rotation or pseudorotation in a molecule or a solid and the corresponding rotational g factor are formulated using the Berry-phase technique and standard density functional plane wave methods. Among the simplest molecules, H+2, H2, C2H2, CH4, and CF4, with known rotational g factors, are used as test cases with excellent results. Alternative, faster localized orbital calculations including the magnetic coupling through heuristic Peierls phase factors are also tested and found to be viable, though less accurate. Application to pseudorotations is exemplified in benzene. It is proposed that these methods will be suited for application to pseudorotations in solids.     

Surface-reconstruction-switched adsorbate photofragmentation dynamics

Energy-resolved angular distributions of neutral fragments ejected during photoinduced electron transfer reaction of CH3Br on GaAs(100) exhibit three distinct methyl-radical ejection channels. These undergo marked changes when the termination is switched from the Ga-rich c(8 x 2) to the As-rich c(2 x 8). Our observations are consistent with a strong adsorption-site dependence of the dynamics.     

惰性气体对HFCVD沉积金刚石气相基团的影响

发射光谱法是对等离子进行在线诊断的常用方法。在丙酮/H_2、丙酮/H_2/He和丙酮/H_2/Ar三种体系中,对热丝化学气相沉积金刚石薄膜过程中的等离子体进行了在线测量。研究了不同体积分数的惰性气体对等离子体中各活性基团强度的影响,以及CH,Hβ与C_2的相对强度的比值、电子温度的大小随惰性气体体积分数的变化关系。结果表明,各基团的强度随着惰性气体体积分数的增加呈现上升趋势,且加入同体积分数的氩气比加入氦气的影响更大;CH,Hβ与C_2的相对强度比值、电子温度随着惰性气体体积分数的增加而呈现下降趋势,且在丙酮/H_2/Ar体系中要比丙酮/H_2/He体系中小。     

N-取代酰胺-二苯酮体系光化夺氢反应活泼自由基的ESR研究

本文用自由基捕捉剂2,3,5,6-四甲基亚硝基苯(ND)及苯亚甲基叔丁基氮氧化物(PBN)与ESR相结合的方法研究了十二种取代酰胺RC₆H₄NHC(0)CH₃(R-CH₃、Cl、Br、H、NO₂)、C₆H₅N(R)C(0)CH₃(R=CH₃、C₂H₅)及HC(0)NR₂(R-CH₃、C₂H₅)与二苯酮光化夺氢反应中的活泼自由基。结果表明: 1.对于RC₆H₄NHC(0)CH₃,二苯酮夺取氮上H形成R-C₆H₄NC(0)CH₃自由基。 2.对C₆H₅N(R)C(0)CH₃及HC(O)NR₂,二苯酮夺取与羰基相连的甲基氢、羰基上氢及与N相连碳上的氢分别形成 C₆H₅N(R)C(0)CH₂、C(0)NR₂、C₆H₅N(CHR')C(0)CH₃及。     

Gas-phase deprotonation of arylalkylamines. A collision-induced dissociation study

The collision-induced dissociation (CID) of deprotonated arylalkylamines of general formula R(1)C(6)H(4)CHR(2)CH(2)NR(3)(2) (where R(1) = H, OH, F or NO(2); R(2) = H or OH; R(3) = H or CH(3)) generated by negative chemical ionization with H(2)O and D(2)O as ionizing reagents, is discussed. The negative chemical ionization mass spectra show that, in the absence of a hydroxy group in the aromatic ring, deprotonation takes place at the benzylic position whereas the proton is lost from the OH group when present. The nitro compound forms only M(-.) ions. The CID spectra of the deprotonated molecules show that fragmentations are strongly dependent on the structural features of the molecules, namely the presence or absence of substituents in the aromatic ring or aliphatic chain. Copyright 1999 John Wiley & Sons, Ltd.     

Fragmentation of water by heavy ions

Absolute cross sections for fragmentation of water molecules by C3+ and O5+ ions over an energy region where the Bragg peak maximizes were measured for ionization, electron capture, and electron loss channels. A collision regime where sigmaSigmaOq+> or =sigmaH2O+ was reached for the first time, producing large abundances of H+ and O+ fragments in comparison to proton impact. Our findings have straightforward implications in the subsequent fast chemistry at the ionization site and on the O production in the first stages of water radiolysis. An unexpected channel-independent relationship between the cross sections for the fragmentation products, which is also approximately independent of the particle type, energy, and charge state, is found. A model is presented to explain such behavior allowing the cross sections of all fragmentation products to be obtained from single and double electron removal cross sections.     

丁酮分子的多光子电离-离解机理

研究了丁酮分子经(n0,3d)共振的多光子电离-离解机理(MPID).多光子电离-飞行时间质谱测得的主要离子产物是C2H3O+和CH3CH+2,C2H3O+的强度为CH3CH+2的2～5倍,还有少量C2H+2,C2H+3和CH+3离子,未见到母体离子.主要离子产物的分质量多光了电离谱结构相似,而各离子产物的光强指数不同.实验结果说明丁酮分子的多光子电离-离解机理符合母体离子阶梯模型,文中用梯开关模型对主要产物离子的产生机理进行了解释.     

乙胺分子的多光子电离过程质谱研究

报道了乙胺分子在４４０～４７５ｎｍ波长范围内多光子电离（ＭＰＩ）质谱（ＭＳ）研究结果。碎片离子主要由母体离子碎裂模式产生。母体离子ＣＨ３ＣＨ２Ｎ＋·Ｈ２由经３ｓ里德堡态的（２＋２）共振多光子电离产生后，大部分发生β键断裂，形成ＣＨ２＝Ｎ＋Ｈ２离子，还有一部分再吸收一个光子，通过Ｃ－Ｈ（ＣＨ２）键的断裂产生了ＣＨ３ＣＨ＝Ｎ＋Ｈ２离子。ＣＨ３ＣＨ＝Ｎ＋Ｈ２和ＣＨ２＝Ｎ＋Ｈ２离子最容易发生的碎裂过程是脱去氢分子，分别产生Ｃ２Ｈ４Ｎ＋（分子式）离子和ＣＨ≡Ｎ＋Ｈ离子。     

Kinematically complete final state investigations of molecular photodissociation: two- and three-body decay of laser-prepared H 3 3 s ? 2 A 1 '

We have performed kinematically complete investigations of molecular photodissociation of triatomic hydrogen in a fast beam translational spectrometer recently built in Freiburg. The apparatus allows us to investigate laser-induced dissociation of neutral molecules into two, three, or more neutral products. The fragments are detected in coincidence and their vectorial momenta in the center-of-mass frame are determined. We demonstrate the potential of the method at the fragmentation of the 3 s ² A ₁ ^′ ( N = 1, K = 0) state of triatomic hydrogen. In this state, three-body decay into ground state hydrogen atoms H+H+H, two-body predissociation into H+H ₂ (v , J), and photoemission to the H ₃ ground state surface with subsequent two-body decay are competing channels. In the case of two-body predissociation, we determine the rovibrational population in the H ₂ (v , J) fragment. The vibrational distribution of H ₂ is compared with approximate theoretical predictions. For three-body decay, we measure the six-fold differential photodissociation cross-section. To determine accurate final state distributions, the geometric collection efficiency of the apparatus is calculated by a Monte Carlo simulation, and the raw data are corrected for apparatus efficiency. The final state momentum distribution shows pronounced correlation patterns which are characteristic for the dissociation mechanism. For a three-body decay process with a discrete kinetic energy release we have developed a novel data reduction procedure based on the detection of two fragments. The final state distribution determined by this independent method agrees extremely well with that observed in the triple-coincidence data. In addition, this method allows us to fully explore the phase space of the final state and to determine the branching ratios between the two- and three-body decay processes. Received 29 March 2001