Monitoring the reaction between AICl3 and o-xylene by using terahertz spectroscopy

Terahertz time-domain spectroscopy （THz-TDS） is used to study the interaction between AlCl3 and o-xylene in a temperature range from 300 K to 368 K. For comparison, the three isomers of o-, m-, and p-xylene are measured by using THz-TDS. The o-xylene carries out isomerization reaction in the presence of catalyst AlCl3. The absorption coefficient of the mixed reaction solution is extracted and analyzed in the frequency range from 0.2 THz to 1.4 THz. The temperature dependence of the absorption coefficient, which is influenced by both the dissolution of AlCl3 and the production of the two other isomer resultants, is obtained, and it can indicate the process of the isomerization reaction. The results suggest that THz spectroscopy can be used to monitor the isomerization reaction and other reactions in chemical synthesis, petrochemical and biomedical fields.     

Photophysical characteristics of polyaniline with photochromic azobenzene side groups

Photochromic characteristics and optical molecular reorientation in conducting polymer such as polyaniline derivatives containing photochromic azobenzene moieties (PAPNPAPOA) in side chain are studied. Changes in the UV—vis absorption, refractive index, thickness, contact angle and morphology of these films after irradiation of a linearly polarized light with a wavelength of 365nm are measured. The trans-cis isomerization of PAPNPAPOA is proved irreversible even after withdrawing the UV light for a long time. That the structure of main-chain attends by the trans-cis isomerization of side-chain is confirmed by the absorption and the solution colour during the UV irradiation. These effects are discussed by taking the trans-cis isomerization of azobenzene into consideration.     

Excellent acetone sensing properties of porous ZnO

Porous Zn O was obtained by hydrothermal method.The results of scanning electron microscope revealed the porous structure in the as-prepared materials.The acetone sensing test results of porous Zn O show that porous Zn O possesses excellent acetone gas sensing properties.The response is 35.5 at the optimum operating temperature of 320?C to 100 ppm acetone.The response and recovery times to 50 ppm acetone are 2 s and 8 s,respectively.The lowest detecting limit to acetone is 0.25 ppm,and the response value is 3.8.Moreover,the sensors also exhibit excellent selectivity and long-time stability to acetone.     

Diffraction grating single-shot correlation system for measurement of picosecond laser pulses

We study and experimentally demonstrate a sensitive single-shot correlation system in which only a diffraction grating is used to produce a transverse time delay (TTD) in the reference pulse.The mechanism of the TTD introduced by the grating and the formation of the relative time delay (RTD) in the noncollinear correlation system are analyzed in detail.By using our system,we successfully measured the temporal duration of picosecond laser pulses,and a time resolution of ～0.047 ps is obtained at 1047 nm.The impact of the grating dispersion and the second harmonic beam walk-off effect on the measurement are considered.     

Effect of power scale of 974 and 633 nm lasers on the induced loss at 633 nm of Yb~(3+)/Al~(3+) co-doped silica fiber

Induced loss at 633 nm is tested in Yb~(3+)∕Al~(3+)co-doped silica fiber by a core pumped with a 974 nm laser and probed with a 633 nm laser. The fiber is prepared by the modified chemical vapor deposition method combined with solution doping. Different power scales of pump light and probe light are used in the tests. It is found that there is a dynamic equilibrium between photobleaching induced by 633 nm probe light and photodarkening(PD)induced by 974 nm pump light. For the first time to our knowledge, the effect of 633 nm probe laser power on an induced loss test of Yb~(3+)∕Al~(3+)co-doped silica fiber is studied quantitatively. It suggests that as long as the633 nm probe light power is less than 0.2 m W, the induced loss is mainly contributed by the PD effect of pumping light, and the deviation of induced loss is less than 5%.     

Transient Properties of a Bistable System with Delay Time Driven by Non-Gaussian and Gaussian Noises： Mean First-Passage Time

The mean first-passage time of a bistable system with time-delayed feedback driven by multiplicative non-Gaussian noise and additive Gaussian white noise is investigated. Firstly, the non-Markov process is reduced to the Markov process through a path-integral approach; Secondly, the approximate Fokker-Planck equation is obtained by applying the unified coloured noise approximation, the small time delay approximation and the Novikov Theorem. The functional analysis and simplification are employed to obtain the approximate expressions of MFPT. The effects of non-Gaussian parameter （measures deviation from Gaussian character） r, the delay time τ, the noise correlation time to, the intensities D and a of noise on the MFPT are discussed. It is found that the escape time could be reduced by increasing the delay time τ, the noise correlation time τ0, or by reducing the intensities D and α. As far as we know, this is the first time to consider the effect of delay time on the mean first-passage time in the stochastic dynamical system.     

Relaxation of Dense Electron Plasma Induced by Femtosecond Laser in Dielectric Materials

Electron plasma induced by a focused femtosecond pulse （130 fs, 800 nm） in dielectric materials （Soda Lime glass, K9 glass, and SiO2 crystal） is investigated by pump-probe shadow imaging technology. The relaxation of the electron plasma in the conduction band is discussed. In SiO2 crystals, a fast self-trapping process with a trapping time of 150fs is observed, which is similar to that in fused silica. However, in Soda Lime glass and K9 glass, no self-trapping occurs, and two decay processes are found： one is the energy relaxation process of conduction electrons within several picoseconds, another is an electron-hole recombination process with a timescale of lOOps. The electron collision time T in the conduction band is also measured to be in the order of 1 fs in all of these materials.     

Three-step lithography to the fabrication of vertically coupled micro-ring resonators in amorphous silicon-on-insulator

A simple method to fabricate vertically coupled micro-ring resonators in amorphous silicon-on-insulator is created by a three-step lithography process. First, the linear loss at 1.55 μm of the a-Si:H film is calculated to be 0.2 0.05 d B∕cm. Then, the bottom line waveguide of Su-8 with a flat top surface of 300 nm is created by etching. The thickness of Su-8 can easily be controlled by the etching time. Finally, by opening the window pattern and etching several layers, the first layer marks made by electron beam lithography are found with a50 nm resolution, and the high quality of the micro-ring resonator is demonstrated.     

Investigation of ultrafast dynamics of CdTe quantum dots by femtosecond fluorescence up-conversion spectroscopy

The ultrafast carrier relaxation processes in CdTe quantum dots are investigated by femtosecond fluorescence upconversion spectroscopy.Photo-excited hole relaxing to the edge of the forbidden gap takes a maximal time of ～ 1.6 ps with exciting at 400 nm,depending on the state of the photo-excited hole.The shallow trapped states and deep trap states in the forbidden gap are confirmed for CdTe quantum dots.In addition,Auger relaxation of trapped carriers is observed to occur with a time constant of ～ 5 ps.A schematic model of photodynamics is established based on the results of the spectroscopy studies.Our work demonstrates that femtosecond fluorescence up-conversion spectroscopy is a suitable and effective tool in studying the transportation and conversion dynamics of photon energy in a nanosystem.     

Fourier and Wavelet Transform Analysis of Pressure Signals during Explosive Boiling

The transient pressure in a liquid-pool during explosive boiling of acetone is measured by a micro-pressure-measuring system. The Fast Fourier transform and continuous wavelet transform methods are applied to investigate the frequency characteristics. The results show that the dominant frequency of the explosive boiling is 0-2 MHz, and the bubble cluster formed by numerous tiny bubbles departs twice. Analysis and discussions are also conducted to explain the bubble evolution during the explosive boiling.     

Acetone: isomerization and aggregation

The advanced experimental and theoretical techniques enable us to obtain information on the rearrangement of atoms or molecules in a reaction nowadays. As an example, we report on our research work on acetone isomerization and aggregation to give an insight into the reaction pathways, the products and their structures, and the growth regularity of aggregation. The evidences on the structural change of acetone and the stability of acetone clusters are found by a laser ionization mass spectrometer and the results are interpreted from theoretical analysis based on the DFT/B3LYP method. Various isomerization channels of acetone have been established and the optimal structures of the neutral clusters (CH₃COCH₃)_n and the protonated acetone clusters (CH₃COCH₃)_nH⁺ for n=1–7 have been determined.     

偶氮侧基聚合物光致异构动力学研究

本文对偶氮侧基聚合物相位共轭光时间特性进行了研究,得到了相位共扼光产生机制─光致异构过程的时间常数.在相位共轭光上升阶段,其时间常数在0.4～0.5s之间,在相让共轭光的衰减过程,衰减满足双指数关系,分段拟合得到较好的结果,且得到快过程的时间常数为0.27s,慢过程的时间常数为0.78s.     

Time-resolved dynamics of thermal isomerization in cesium-halide cluster anions

We have performed time-resolved studies of the dynamics of thermal isomerization occurring in certain cesium-halide cluster anions. Using a pump-probe technique, we have observed the repopulation of a photodepleted isomer within an ensemble as a function of time by monitoring the photoelectron spectrum. The rates of isomerization increase and the isomer lifetimes decrease as functions of temperature. The clusters undergo a gradual phase transition from solid-like to liquid-like states with liquid-like behavior obtained at approximately 500 K, much lower than the bulk melting temperatures of approximately 900 K.     

Investigation of different liquid media and ablation times on pulsed laser ablation synthesis of aluminum nanoparticles

Aluminum nanoparticles were synthesized by pulsed laser ablation of Al targets in ethanol, acetone, and ethylene glycol. Transmission Electron Microscope (TEM) and Scanning Electron Microscope (SEM) images, Particle size distribution diagram from Laser Particle Size Analyzer (LPSA), UV-visible absorption spectra, and weight changes of targets were used for the characterization and comparison of products. The experiments demonstrated that ablation efficiency in ethylene glycol is too low, in ethanol is higher, and in acetone is highest. Comparison between ethanol and acetone clarified that acetone medium leads to finer nanoparticles (mean diameter of 30 nm) with narrower size distribution (from 10 to 100 nm). However, thin carbon layer coats some of them, which was not observed in ethanol medium. It was also revealed that higher ablation time resulted in higher ablated mass, but lower ablation rate. Finer nanoparticles, moreover, were synthesized in higher ablation times.     

Ultrafast extreme ultraviolet induced isomerization of acetylene cations

Ultrafast isomerization of acetylene cations ([HC=CH](+)) in the low-lying excited A(2)Σ(g)(+) state, populated by the absorption of extreme ultraviolet (XUV) photons (38 eV), has been observed at the Free Electron Laser in Hamburg, (FLASH). Recording coincident fragments C(+) + CH2(+) as a function of time between XUV-pump and -probe pulses, generated by a split-mirror device, we find an isomerization time of 52±15 fs in a kinetic energy release (KER) window of 5.8相似文献   

Isomeric orientation by two-photon excitation: a theoretical study

I develop the theory of molecular orientation induced by two-photon isomerization. Phenomenologically, two-photon isomeric orientational hole burning and reorientation induce molecular orientation while rotational diffusion tends to randomize it. Using the formalism of Legendre polynomials solves the general equations of the theory, and analytical solutions are derived for actual physical cases at the early time evolution and the steady state of two-photon excitation. The theory explains the observed results of two-photon molecular orientation, and predicts additional experiments in this direction. The isomerization parameters and the movement of the isomers during polarized two-photon excitation can be quantified by the analytical theory. A theoretical study on the creation of molecular orientation by competing orientational Kerr effect and two-photon orientation is also presented.     

掺杂Ag纳米粒子对偶氮聚合物光致异构效应的影响

报道了通过宏观测量偶氮聚合物光致异构效应,及其引起的光学各向异性变化,讨论了一种影响偶氮聚合物顺反异构效应的有效途径。在偶氮高分子聚合物中,添加了不同浓度的Ag纳米粒子,采用了波长为442nm的He-Cd偏振激光为激发光源,当Ag纳米粒子掺杂质量浓度为0.12μg/ml的时候,激发了薄膜样品中Ag纳米粒子的等离子体共振效应,增强了粒子周围纳米尺度的电磁场强度,相当程度上提高了偶氮聚合物光致异构的转换效率;另外,研究了不同的取代基同纳米Ag粒子的相互作用对光致异构效应的影响,探讨了一种能够有效地控制光致异构效应的方法。     

Mechanisms of molecular response in the optimal control of photoisomerization

We report on adaptive feedback control of photoinduced barrierless isomerization of 1,1'-diethyl-2,2'-cyanine in solution. We compare the effect of different fitness parameters and show that optimal control of the absolute yield of isomerization (photoisomer concentration versus excitation photons) can be achieved, while the relative isomerization yield (photoisomer concentration versus number of relaxed excited-state molecules) is unaffected by adaptive feedback control. The temporal structure of the optimized excitation pulses allows one to draw clear mechanistic conclusions showing the critical importance of coherent nuclear motion for the control of isomerization.     

Semiphenomenological analysis of cis-to-trans isomerization of polyacetylene

Semiphenomenological analysis of cis-to-trans isomerization process of polyacetylene is presented. It is shown that excitation of cis-transoid form to trans-cisoid form is necessary in the course of the isomerization. The probability of tunneling of a π electron from trans-cisoid to cis-transoid state is estimated to be about 0.7 per second. The life time of trans-cisoid form can be inferred to be several hours.     

Visualization of Crevice Flow in an Engine Using Laser-Induced Fluorescence

A simultaneous visualization technique of reacting and unburned zones using laser-induced fluorescence (LIF) was applied to a high-pressure combustion field in an engine cylinder. Crevice flow from a crevice between a piston and a cylinder wall of a spark ignition gas engine was visualized by LIF of OH and acetone. OH was excited simultaneously with acetone that was seeded into fuel as a tracer by an excitation light at 283.92 nm. Fluorescence signals from each species were detected individually by two intensified CCD cameras using optical band-pass filters which transmit fluorescence wavelength of OH and acetone, respectively. Pressure- and temperature-dependence of LIF signals from each species were evaluated. From the visualized images, it was clarified that oxidation of the crevice flow is stopped at the time of exhaust valve opening. Effects of exhaust port pressure on the oxidation process were investigated.