H+HD→H2+D反应的高分辨交叉分子束实验研究

本文利用交叉分子束方法和离子速度成像技术,对H+HD→H₂+D反应在1.17 eV碰撞能下的态-态反应动力学开展了高分辨实验研究. 实验采用1+1''(真空紫外+紫外)近阈值激光电离方式对反应中的D原子产物进行探测,获得了高角度分辨和高能量分辨的产物离子速度影像,进而精确获得了反应的态-态微分截面. 实验观测到了H₂(v''=0,j''=1)和H₂(v''=0,j''=3)振转产物角分布中与散射过程的干涉效应相联系的前向散射振荡. 这一研究进一步表明了化学反应微分截面的精确测量在气相态-态反应动力学研究中的重要性.     

碰撞能44∽164 cm−1范围内单量子态转动激发对F+D2反应的影响

当碰撞能很低,尤其是远低于反应势垒的时候,反应通常经过量子隧穿来进行. 目前,还没有明确的物理图像来描述反应物的转动激发对这类反应过程的影响. 本文基于里德堡态D原子飞行时间谱探测方法,利用多通道探测器交叉分子束装置研究了碰撞能44 cm^-1∽164 cm^-1下反应F+D₂(v=0,j=0,1)→DF(v'')+D的动力学过程,并得到了振动态分辨的微分截面. 在可资用能相等时,通过调控反应的平动能,研究了D₂转动激发对于反应的影响,发现反应物的转动比平动更有利于反应的进行. D₂的转动激发导致产物DF的角分布和量子态分布发生显著变化. 本工作进一步加深转动激发对于反应的影响的理解,尤其是在反应能量远低于反应势垒的情况下.     

交叉分子束实验研究F+D2(v=1, j=0)反应

本文使用交叉分子束方法研究了氟原子和振动激发态氘分子D₂(v=1, j=0)的反应. 使用受激拉曼抽运的方法制备了振动激发的D₂分子. 实验中未观测到来自于旋轨耦合激发态氟原子F^*(²P_1/2)与振动激发态D₂分子的贡献. 观测到来自于旋轨耦合基态氟原子F(²P_3/2)和振动激发态D₂的反应信号,相应的产物DF分子布居于v''=2,3,4,5振动态上. 与振动基态反应F+D₂(v=1,j=0)相比,振动激发态反应F+D₂(v=1,j=0)生成的DF产物转动分布更“热”. 获得了振动激发反应的四个碰撞能在0.32至2.62 kcal/mol范围内的微分反应截面. 在最低的碰撞能0.32 kcal/mol下,所有振动态的DF产物都以后向散射为主. 随着碰撞能的增加,DF产物的角分布逐渐从后向转移到侧向. 测量了DF(v''=5)产物的前向微分散射截面随碰撞能变化的曲线. 前向散射的DF(v''=5)信号出现于1.0 kcal/mol. 在2.62 kcal/mol碰撞能下DF(v''=5)主要为前向散射.     

超高碰撞能23.84 kJ/mol下反应F+D2→DF+D的交叉分子束研究

本文搭建了一套新的实验设备,首次将氢原子里德堡态标记的飞行时间谱技术与激光爆破束源技术相结合,进行超高碰撞能下化学反应的动力学研究. 初步进行了F+D₂→DF+D在超高碰撞能23.84 kJ/mol下的实验研究. 在研究中应用了两种类型束源：一类是通过激光爆破过程产生的高能F原子束源,另一类是通过液氮冷却脉冲阀而产生的D₂束源. 实验中探测了反应产物振动态分辨的微分散射截面. 结果显示,大部分反应产物DF主要呈现侧向和后向散射分布,而产物DF(v''=4)则主要分布在前向. 对前向散射产物DF(v''=4)的动力学来源进行了讨论.     

HOBr/DOBr态到态光解动力学的量子波包研究

本文基于高水平的多参考组态相互作用计算,报导了HOBr的最低三个单重态的三维势能面. 并且对该分子的光解离过程用实波包传播的方法进行了量子动力学研究,不仅计算结果得到了吸收光谱,而且还产生了光解产物的内态和角度分布. 结果与在紫外区域测得的HOBr的总吸收截面定量吻合,并很好的重现了实验上在266 nm处观察到的振动冷和转动热的光解OH/OD产物. 此外,预测了OH/OD的反冲各向异性参数接近平行跃迁的极限值,表明在266 nm处从基态(1¹A'')到2¹A''态的面内跃迁是一个快速的解离过程. 这与实验上从测量转动取向得出的结论一致. 然而,想要实现与实验上的定量一致,还需要考虑自旋和电子角动量的影响.     

OCS分子在里德堡F态的真空紫外光解动力学：S(3PJ=2,1,0)产物通道

本文利用可调谐真空紫外光源和时间切片离子速度成像技术研究了OCS分子的真空紫外光解动力学. 在对应OCS里德堡F态的五个光解波长下(133.26 nm∽139.96 nm)实验采集了S(³P_J=2,1,0)产物的离子影像,从中发现了两个解离通道：S(³P_J=2,1,0)+CO(X¹Σ⁺)和S(³P_J=2,1,0)+CO(A³π),其中前者为主要通道. 离子影像中CO产物的振动结构可部分分辨. 从离子影像中提取出了S(³P_J=2,1,0)+CO(X¹Σ⁺)通道的产物总平动能分布、各向异性参数和CO振动态分支比等信息. 发现了对应OCS在F态的几个低振动态下光解的产物各向异性参数取负值,而对应F态的几个高振动态下光解产物的各向异性参数为正值. 另外,同一光解波长下三种S产物S(³P₂)、S(³P₁)和S(³P₀)的各向异性参数也不相同. 经分析,这些现象可能来源于激发区域的其它不同对称性的电子态的贡献,从而导致解离过程中同时存在平行解离和垂直解离. 本工作有利于进一步理解OCS真空紫外光解中的非绝热耦合作用.     

青蒿素光化学合成中二氢青蒿酸与单线态氧反应的动力学研究

青蒿素是一种优异的抗疟药,广泛用于临床医学. 但由于青蒿素天然来源的限制,青蒿素的化学合成一直受到高度关注. 二氢青蒿酸是合成青蒿素的关键前体. 二氢青蒿酸与单线态氧反应形成过氧化物是青蒿素光化学制备中的关键步骤,制约着青蒿素化学合成的产率. 然而关于二氢青蒿酸与单线态氧反应的重要动力学信息并未有报道. 本文通过光敏化法产生单线态氧,研究二氢青蒿酸与单线态氧之间的反应速率常数. 通过直接检测单线态氧在1270 nm处的发光衰减动力学,得出单线态氧与二氢青蒿酸在不同溶剂中的反应速率常数分别为：在CCl₄中为1.81×10⁵ (mol/L)^-1·s^-1,在CH₃CN中为5.69×10⁵ (mol/L)^-1·s^-1,DMSO中为3.27×10⁶ (mol/L)^-1·s^-1. 发现在三种溶剂中二氢青蒿酸与单线态氧的反应速率常数随着溶剂极性的增加而增加. 这些结果为优化青蒿素光化学合成的实验条件提供了基础知识,有助于提高青蒿素的合成效率.     

OCS经由F 31Π里德堡态生成CO(X1Σ+)+S(1D2)产物的波长相关性光解离

本文利用时间切片离子速度成像技术在134∽140 nm波段研究了OCS分子经由F 3¹Π里德堡态的真空紫外光解离动力学. 在选取的5个分别对应OCS(F 3¹Π, v₁=0∽4)的伸缩振动激发的光解波长,实验测得了来自CO(X¹Σ⁺)+S(¹D₂)产物通道的SS(¹D₂))实验影像,并获得了总平动能谱和CO(X¹Σ⁺, v)共生产物的振动布居及角分布. 结果分析表明OCS分子解离生成CO(X¹Σ⁺)+S(¹D₂)产物的过程经历了上态F 3¹Π 与C_?v和C_s构型的下电子态间非绝热耦合过程. 实验结果显示了很强的波长相关性：OCS (F 3¹Π, v₁)的较低转动激发态(v₁=0∽2)和较高转动激发态(v₁=3, 4)的CO(X¹Σ⁺)产物的振动布居和角分布具有显著差异,表明该解离过程中具有不同的解离机理. 本结果提供了振动耦合可能对真空紫外光解离动力学产生关键作用的相关证据.     

二硫化碳分子在204 nm附近的光解离动力学研究：S(3PJ)+CS(X1Σ+)产物通道

本文用时间切片离子速度影像技术研究CS₂分子在204 nm附近的光解离动力学. 在201.36、203.10、204.85和206.61 nm这四个解离波长下,实验清楚地观测到S(³P_J)+CS(X¹Σ⁺)产物通道. 在实验获得的S(³P_J=2,1,0)影像中,对应的CS(X¹Σ⁺)产物的振动态结构得到了部分的分辨. 通过对影像的分析,还获得了解离的总平动能谱以及产物的各项异性参数. 实验观察到的相对小的各项异性参数表明产物更倾向于经历了间接的光解离过程. 这一通道的自旋－轨道禁阻特征也说明了非绝热效应在二硫化碳紫外光解离生成S(³P_J=2,1,0)+CS(X¹Σ⁺)的过程中发挥了重要作用.     

羟基自由基双光子激发解离动力学

本文利用高里德堡态氢原子飞行时间探测技术,研究了羟基自由基的双光子激发解离动力学. H(²S)+O(¹D)和H(²S)+O(¹S)解离通道是由于羟基在经由A²Σ⁺(v''=2, J''=0.5-2.5)中间态通过双光子激发最终到排斥性的激发态势能曲线2²Ⅱ和B²Σ⁺上产生. 这两种解离通道产物都具有各向异性的角向分布,其中H(²S)+O(¹D)产物角分布异向因子β为-0.97,H(²S)+O(¹S)产物角分布异向因子β为1.97. 各向异性的角向分布与OH自由基在排斥性的激发态势能曲线上直接解离机理相吻合. 此实验观测到羟基自由基的解离能为35580±15 cm^-1.     

Guided-Wave Two-Dimensional Acousto-Optic Scanner Using Proton-Exchanged Lithium Niobate Waveguide

Two-dimensional scanning of a 0.6328 mum guided-light beam has been realized using noncolinear acousto-optic (AO) coplanar Bragg diffraction together with colinear AO guided-mode to substrate radiation-mode conversion in a Z-cut Xpropagation LiNbO3 proton-exchanged (PE) waveguide. The two surface acoustic (SAW) waves utilized are at the center frequencies of 500 and 200 MHz, propagating in the Y and X axes, respectively. Two-dimensional scanning of approximately 720 resolvable light beam spots, namely, 18 40 (horizontal vertical) scanning, has been demonstrated using a light beam of 1.0 mm aperture. The total number of resolvable beam spots can be greatly increased from 720 by simply utilizing SAW transducers of larger bandwidth and a light beam of greater aperture. It should also be possible to significantly increase the diffraction efficiency from 3 % by optimizing the parameters of the PE waveguide and the SAWs.     

Effect ofγ-radiation on the spectral luminescence characteristics of impure cadmium tungstate crystals

Results of a study of the effect of γ-radiation on the spectral luminescence properties of cadmium tungstate crystals doped with silver, bismuth, and molybdenum cations are presented. Spectral characteristics of the nondnnnoped crystals are briefly described. Absorption and photo and X-ray luminescence spectra of the crystals taken before and after exposure to γ-radiation (5.5·10⁴ Gy) are compared. It is found that the spectral characteristics of the crystals doped with silver, bismuth, and molybdenum cations do not change markedly after the exposure. The relation between the type of impurity-induced defects, individual characteristics of the impurity cations, and the character of the effect of γ-radiation on the spectral luminescence properties of impure crystals is analyzed (preliminarily). Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 64, No. 1, pp. 55–60, January–February, 1997.     

Femtosecond Transform-Limited Pulse Generation by Compensating for the Linear Chirp of SPM Spectra in Dispersion Shifted Fibers

A simple technique of pulse compression, based on the linear chirp compensation of self-phase modulation (SPM) spectra in dispersion shifted fibers, is demonstrated. The optimization procedure is carried out, for a short span of a single-mode fiber, using a parabolic law, which describes the behavior of the squared output pulse width versus the pump peak power in the case of Gaussian pulses. The experimental results give a minimum pulse duration of 233 fs, which is in good agreement with the model. Shorter and coherent pulses, down to 90 fs, have been obtained by inserting an interference filter at the optical output.     

Sorting of bending magnets for the SSRF booster

The Shanghai Synchrotron Radiation Facility(SSRF)booster ring,a full energy injector for the storage ring,is deigned to accelerate the electron beam energy from 150MeV to 3.5GeV that demands high extraction efficiency at the extraction energy with low beam loss rate when electrons are ramping.Closed orbit distortion(COD)caused by bending magnet field uniformity errors which affects the machine performance harmfully could be effectively reduced by bending magnet location sorting.Considering the affections of random errors in measurement,both ideal sorting and realistic sorting are studied based on measured bending magnet field uniformity errors and one reasonable combination of bending magnets which can reduce the horizontal COD by a factor of 5is given as the final installation sequence of the booster bending magnets in this paper.     

Measurement of nonlinear coefficient of optical fiber based on small chirped soliton transmission

We measure the waveform and phase curves of short optical pulses before and after transmission over different lengths of fibers by use of the pulse analyzer with the frequency-resolved optical gating (FROG),and numerically simulate pulse evolution under the experimental conditions.The nonlinear coefficient of the fiber is given by comparing the experimental results with the numerical ones.Difference between the experiment and numerical simulation is analyzed.     

Resonance scattering of canonical elastic shells in absorbing fluid medium

Resonance scattering of elastic spherical shell and cylindrical shell while the surrounding fluid medium has absorption is studied. The normal mode solution derived using exact elastic theory and the separation of variables is still applicable. However, the scattering form function has to be modified for the absorbing medium, otherwise the unreasonable result would be obtained. The backscattering form function in the absorbing medium is redefined, and the form function of elastic spherical and cylindrical shell with vacuum or solid matter filled is calculated in various absorption conditions. The results show that the absorption of surrounding fluid leads to notable attenuation of the coincidence resonances in the mid-frequency, but it has a little influence on the low-frequency resonance scattering induced by the filler inside the shell.     

Single-beam self-referenced phase-sensitive surface plasmon resonance sensor with high detection resolution

A versatile and low-cost single-beam self-referenced phase-sensitive surface plasmon resonance(SPR)sensing system with ultra-high resolution performance is presented.The system exhibits a root-mean-square phase fluctuation of ±0.0028.over a period of 45 min.i.e.a resolution of±5.2×10-9 refractive index units.The enhanced performance has been achieved through the incorporation of three design elements:a true single-beam configuration enabling complete self-referencing so that only the phase change associated with SPR gets detected,a differential measurement scheme to eliminate spurious signals not related to the sensor response,and the elimination of retardation drifts by incorporating temperature stabilization in the liquid crystal phase modulato .Our design should bring the detection sensitivity of non-labeling SPR biosensing closer to that achievable by conventional fluorescence-based techniques.     

Influences of SiO2 protective layers and annealing on the laser-induced damage threshold of Ta2O5 films

Ta2O5 films are prepared on BK7 substrates with conventional electron beam evaporation deposition.The effects of SiO2 protective layers and annealing on the laser-induced damage threshold (LIDT) of the films are investigated.The results show that SiO2 protective layers exert little influence on the electric field intensity(EFI)distribution,microstructure and microdefect density but increase the absorption slightly.Annealing iS effective on decreasing the microdefect density and the absorption of the films.Both SiO2 protective layers and annealing are beneficial to the damage resistance of the films and the latter is more effective to improve the LIDT.Moreover,the maximal LIDT of Ta2O5 films is achieved by the combination of SiO2 protective layers and annealing.     

A stereo matching algorithm using multi-peak candidate matches and geometric constraints

Gray cross correlation matching technique is adopted to extract candidate matches with gray cross correla- tion coefficients less than some certain range of maximal correlation coefficient called multi-peak candidate matches. Multi-peak candidates are extracted corresponding to three closest feature points at first. The corresponding multi-peak candidate matches are used to construct the model polygon. Correspondence is determined based on the local geometric relations between the three feature points and the multi-peak candidates. The disparity test and the global consistency checkout are applied to eliminate the remaining ambiguous matches that are not removed by the local geometric relational test. Experimental results show that the proposed algorithm is feasible and accurate.