在Au(111)表面酞菁单分子与钴原子可控金属化反应（英文）

本文利用低温扫描隧道显微术和第一性原理计算研究了吸附在Au(111)表面的酞菁分子(_H2Pc)与Co原子在单分子水平上的金属化反应过程.通过扫描探针的操纵手段,以可控的方式原位实现了单个H2Pc分子与钴原子反应生成CoPc的金属化酞菁产物,揭示出源于H_2Pc和Co原子的π-d相互作用的中间过程.结合第一性原理计算和中间产物的图像模拟,进一步阐明了这一氧化还原反应中成键和断键的关键机制,即脱氢和金属化过程并非由Co原子和吡咯环的H作用所致,而与Co原子和吡咯环上的N原子之间的作用有关.     

基质隔离红外光谱结合理论计算研究第五族金属原子和硫化氢反应

利用基质隔离红外光谱结合理论计算,研究了激光溅射获得的第五族金属原子和硫化氢分子的反应. 结果表明金属原子插入H₂S的H-S化学键形成HMSH分子(M=V,Nb,Ta). 对Nb和Ta该HMSH分子重排为H₂MS分子. HMSH分子和H₂S进一步反应生成H₂M(SH)₂分子. 通过D₂S和H₂³⁴S同位素标定确定了产物的分子结构,同时我们用DFT(B3LYP和BPW91)理论计算预测了产物分子的能量、结构和振动频率. 通过DFT IRC计算研究了第五族金属原子和₂S分子的反应机理. HVSH分子通过光照解离为VS和H₂,然后通过退火可以发生VS和H₂复合反应. 计算表明HVSH释放H₂需要16.9 kcal/mol的活化能及吸热13.5 kcal/mol.     

Ca掺杂的氧化铍纳米管吸附H2O和NH3的选择传感特

通过密度泛函计算, 借助NH₃和H₂O分子对未掺杂以及钙掺杂的BeO碳纳米管的结构和电传导性进行了研究. 结果发现,NH₃和H₂O分子可以吸附在纳米管侧壁的Be原子上,吸附能分别为约36.1和39.0 kcal/mol. 态密度分析显示BeO纳米管的电传导性在吸附后稍有变化. 对于NH₃和H₂O分子,纳米管表面的钙原子替换Be原子可使吸附能分别增加约7.4和14.7 kcal/mol. 与未掺杂纳米管不同的是,钙掺杂BeONT吸附NH₃和H₂O分子的电传导性更加敏感,且H₂O分子比NH₃分子更敏感.     

a-Si:H掺杂机理的研究

本文利用CNDO/2量子化学理论方法,对P和B原子在四面体配位的Si₄₆和Sl₄₆H₆₀H₄^*原子集团中置换Si原子前后的原子集团能量和能态分布变化进行了计算.计算结果表明:1)在Si₄₆H₆₀H₄^*原子集团中用P(或B)置换引Si原子后在能隙中明显地出现施主(或受主)态子带,同样在Si_{46相似文献}   

密度泛函理论方法研究6H-SiC(0001)表面对氧分子和水分子的吸附

本文通过密度泛函方法计算6H-SiC(0001)表面对氧分子和水分子的吸附. 在6H-SiC(0001)表面上吸附的O₂分子自发地解离成O^*,并被吸收在C与Si原子之间的空位上. 吸附的H₂O自发地分解成OH^*和H^*,它们都被吸附在Si原子的顶部,OH^*进一步可逆地转化为O^*和H^*. H^*可以使Si悬键饱和并改变O^*的吸附类型,并进一步稳定6H-SiC(0001)表面并防止其转变为SiO₂.     

Li掺杂8-羟基喹啉铝的密度泛函理论研究

采用密度泛函理论研究了Li原子掺杂8-羟基喹啉铝(Alq₃)分子的几何构型、 前线分子轨道及电子转移特性. 研究结果表明, Li原子掺杂Alq₃后, Li原子与Alq₃的O, N原子键合, 形成电子转移复合物. Li原子将部分电子转移到Alq₃的吡啶环上, 在Alq₃的带隙内形成施主能级, 这种n型掺杂结构有效地提高了电子的传输效率; 但过多的Li原子的掺杂会使Alq₃分解, 从而减弱其电子传输能力. 为使Alq₃的电子传输能力达到最高, Li原子的掺杂应保持在2:1左右的比例.     

OH+C2H3F的反应机理及产物支化比反应的理论研究

本文对HOC₂H₃F可能解离通道的势能面进行从头算CCSD(T)/CBS//B3LYP/6-311G(d,p)计算,同时对速率常数进行Rice-Ramsperger-Kassel-Marcus计算. 生成主要产物CH₂CHO+HF最有利的反应途径是OHC₂H₃F→i2→TS14→i6→TS9→i3→TS3→CH₂CHO+HF,其中速率决定步骤是HF通过TS11从CO桥接位置解离,能量比反应物高3.8 kcal/mol. 借助中间态TS14,F原子从C_α迁移到C_β位置生成CH₂O+CH₂F,然后通过中间态TS16,H从O迁移到C_α位置;通过中间态TS5,C-C键断裂生成产物,其能量比反应物低1.8 kcal/mol,比TS11低4.0 kcal/mol.     

F−(H2O)+CH3I配体交换反应动力学

本文介绍F^?(H₂O)+CH₃I→[FCH₃I]^?+H₂O在交叉分子束碰撞能量0.3∽2.6 eV的配体交换动力学成像结果. 产物的动能受到弱键结合配合物的稳定性的影响,大量水分子的内部激发不利于中间物有效的能量重新分配,随着碰撞增加,低动能受到抑制. 在0.3 eV时,内部亲核取代非常重要,为形成I^?和I^?(H₂O)的竞争性亲核取代途径提供了依据.     

氧化石墨烯负载的Pt单原子催化硼胺烷水解机理的理论研究

本文研究了氧化石墨烯负载Pt单原子(Pt₁/Gr-O)催化硼胺烷(NH₃BH₃)全水解反应机理,即一分子的NH₃BH₃生成三分子的氢气(H₂)的过程. 在水解路径中,首先吸附的硼胺烷连续断裂两个B-H键生成第一分子的H₂. 接着,一个H₂O分子与^*BHNH₃基团(^*表示吸附态)反应生成^*BH(H₂O)NH₃,其中伸长的O-H键断裂后形成^*BH(OH)NH₃. 然后,第二个H₂O与^*BH(OH)NH₃反应生成^*BH(OH)(H₂O)NH₃,在指向Pt₁/Gr-O表面的O-H断裂后,生成BH(OH)₂NH₃并脱附到水溶液中. 两个水分子脱氢产生的两个H原子脱附生成第二个H₂分子,且Pt₁/Gr-O催化剂恢复. 脱附后的BH(OH)₂NH₃在水溶液中水解生成第三个H₂分子. 纵观整个水解反应,H₂O分子和^*BHNH₃基团的结合是反应速控步,其反应能垒是16.1 kcal/mol. 因此,Pt₁/Gr-O有希望成为室温催化NH₃BH₃全水解催化剂.     

交叉分子束研究氟原子与1,2-丁二烯反应动力学

利用通用型交叉分子束研究了氟原子与1,2-丁二烯的反应,观测到了C₄H₅F+H反应通道. 测量产物C₄H₅FF在实验坐标下的角度分辨的飞行时间谱,获得了这个通道质心坐标下的产物角分布和动能分布. 实验结果表明,相对于氟原子束方向,产物C₄H₅FF主要是后向散射,同时也有大量的前向散射. 这表明反应通道主要通过长寿命的络合物形成机理进行的,同时也伴有直接的双分子亲核取代反应(SN2)机理.     

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.     

Hybrid Wavelength and Code Division Multiple Access in Optical Networks

A review of schemes for multiple access in fiber optic networks shows that a hybrid of wavelength and code division multiple access (WCDMA) combines the best features of both. In particular, the hybrid scheme retains the large information carrying capacity of wavelength division multiple access (WDMA) and flexibility of code division multiple access (CDMA). In this paper WDMA, optical CDMA (OCDMA), and WCDMA networks are discussed. In OCDMA networks, concept of incoherent and coherent coding including inverse decoding and matched filter is introduced. The delay performance of both WDMA and WCDMA networks, under the simple suboptimum access protocols based on cyclic search, is computed. It has been shown quantitatively that tuning delay significantly affects the delay performance of both WDMA and WCDMA networks. Futhermore, delay performance of WCDMA networks is always better than the WDMA networks for the same tuning delay, load, and number of users.     

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.