Laser Flash Photolysis Mechanism of Anthraquinone-2-Sodium Sulfonate in Pyridine Ionic Liquid/Water Mixed System

The photochemical reaction process of anthraquinone-2-sodium sulfonate （AQS） in the mixture of water （H2O） and N-butylpyridinium tetrafluoroborate （[BPy] [BF4]） was studied using the laser flash photolysis technique. Experimental results show that the excited triplet of AQS （3AQS＊） could react rapidly with H2O and the transient absorption spectra greatly changed by increasing the volume fraction of the ionic liquid （VIL） in [BPy][BF4]/H2O mixtures. The absorbance at 510 nm increased gradually with increasing VIL when 0〈VIL〈0.1. By contrast, the absorbance decreased gradually when VIL〉0.1. Otherwise, the absorbance of the band near 380 nm steadily increased. The apparent kinetic parameters of transient species B and ^3AQS＊ are obtained approximately. 3AQS＊ abstracting hydrogen from [BPy]＋ was also explored. It was deduced that the 350-420 nm band was the superposition of the peaks of 3AQS＊ and AQSH＇. The two reactions of 3AQS＊ with [BPy][BF4] and H2O are a pair of competitive reactions. We also concluded that the entire reaction processes slow down in the case of high [BPy] [BF4] concentrations.

TIME-RESOLVED IR STUDIES OF UV LASER FLASH PHOTOLYSIS OF W(CO)_6 IN C_6H_(12)-CCl_4 AND CCl_4 SOLUTION

Time-resolved IR absorption spectroscopy has been used to atudy the photochemistry of W(CO)_6 in cyclohexane, carbon tetrachloride, and the mixture of carbon tetrachloride and cyelohexane. The reastion of photolytically generated W(CO)_5. C_6H_(12) with CCl_4 was investigated. An intermediate with a lifetime of about 0.5ms, presumably attributed as W(GO)_5.CCl_4, was first observed.

LASER FLASH SPECTROSCOPY STUDIES OF THE ANTHRACENEN,N-DIETHYLANILINE EXCIPLEX FORMATION IN γ-CYCLODEXTRIN

Gamma-cyclodextrin (γ-CD) was used to induce the formation of N,N-diethylaniline (DEA) exciplex in 15:85{φ=0.15)v/v EtOH-H_2O binary mixture.Measurements of the fluorescence spectra of anthracene in the presence or absence of DEA and γ-CD show that γ-CD can form 1:1:1 host/guest-Ⅰ/guest-Ⅱ inclusion complex with anthracene and DEA.

LASER FLASH SPECTROSCOPY STUDIES OF PYRENE EXCIMER IN ACETONITRILE

Formation and decay processes of pyrene excimer in acetonitrile have been measured by laser flash spectroscopy at 475nm,and the dependence of λ_1+λ_2 on the pyrene concentration has also been measured at 290°K.On the basis of these measurements,six rate parameters which describe the behaviour of pyrene excimer system in acetonitrile solution have been evaluated.At 355 nm laser light irradiation,the ΔG of the pyrene excimer formation in acetonitrile is evaluated to be -30.18kJ/mol. This value is quite different from the corresponding ΔG in cyclohexane (-16.72kJ/mol).

Time-resolved laser flash photolysis study on transient reaction between excited triplet state of anthraquinone derivatives (AQS) and 2-deoxythymidine

The transient absorption spectra and kinetics of excited triplet state of anthraquinone derivatives 2-anthraquinonesulfonatesodium (AQS) and 2-deoxythymidine (dT) have been investigated in CH3CN-H2O (97:3) using the time-resolved laser flash photolysis technique (KrF, 248 nm). The absorption spectra of dT radical cation and the radical anion of AQS have been observed. From dynamic and thermodyrnamic analysis, the mechanism of this transient reaction has been initially analysed.

Thermal Diffusivity and Thermal Conductivity of Epoxy-Based Nanocomposites by the Laser Flash and Differential Scanning Calorimetry Techniques

Nanocomposites were fabricated by using a commercial two part epoxy as a matrix and multiwalled carbon nanotubes, graphite fibers and boron nitride platelets as filler materials. Multiwalled carbon nanotubes (MWCNTs) that were produced by chemical vapor deposition were found to produce nanocomposites with better thermal diffusivity and thermal conductivity than the MWCNTs that were produced by the combustion method. Compared to the MWCNTs produced by both methods and graphite fibers, boron nitride produced nanocomposites with the highest thermal conductivity. Specific heat capacity was measured by using differential scanning calorimetry and thermal diffusivity was measured by using the laser flash.

An Improved Thermal Conductivity Measurement Scheme for Macroscopic Graphitic Films Using the Laser Flash Method

Achieving efficient thermal management urges to exploit high-thermal-conductivity materials to satisfy the boosted demand of heat dissipation.It is critical to adopt standardized characterization protocols to evaluate the intrinsic thermal conductivity of thermal management materials.However,for the most representative laser flash method,the lack of standard measurement methodology and systematic description on the thermal diffusivity and influencing factors has led to significant deviations and confusion of the thermal conduction performance in the emerging thermal management application.Here,the measurement error factors of thermal diffusivity by the common laser flash analyzer(LFA)are discussed.Taking high-thermal-conductivity graphitic film(GF)as a typical case,the key factors are analyzed to guide the measurement protocol of related carbon-based thermal management materials.The basic principle of the LFA measurement,actual pre-processing conditions,instrument parameters setting,and data analysis are elaborated for accurate measurements.Furthermore,the graphene thick films and common isotropic materials are also extended to meet various thermal measurement requirements.Based on the existing practical problems,we propose a feasible test flow to achieve a unified and standardized thermal conductivity measurement,which is beneficial to the rapid development of carbon-based thermal management materials.

Photophysical Properties and Photoinduced Electron Transfer between [60] Fullerene-Containing Cyclic Sulphoxide [C_(60)-C_6H_8SO] and Tetrathiafulvalene (TTF) by Laser Flash Photolysis

Photoinduced electron transfer (PET) processes between C 60-C 6H 8SO and Tetrathiafulvalene (TTF) have been studied by nanosecond laser photolysis. Quantum yields (Φ et) and rate constants of electron transfer (k et) from TTF to excited triplet state of fullerene-containing cyclic sulphoxide in benzonitrile (BN) have been evaluated by observing the transient absorption bands in the NIR region. With the decay of excited triplet state of fullerene-containing cyclic sulphoxide, the rise of radical anion of fullerene-containing cyclic sulphoxide is observed.

Photosensitized oxidation of tryptophan and tyrosine by aromatic ketones:A laser flash photolysis study

Photochemical processes of benzophenone （BP） and xanthone （XT） with tryptophan （TrpH） and tyrosine （TyrOH） were stud- ied using the laser flash photolysis technique. It has been observed that the triplet state of BP and XT reacted with TrpH and TyrOH by hydrogen transfer with the formation of BP and XT ketyl radicals and oxidized radicals of Trp＂ and TyrO＇. The re- lated rate constants of these reactions were determined in this paper. The free energy changes （AG） of these reactions suggested that the proposed hydrogen transfer mechanism was thermodynamically feasible. These results provide theoretical foundation for further studying structural effects on the photochemical behaviors of proteins with triplet state BP and XT.

Dual-Wavelength Laser Flash Raman Spectroscopy Method for In-Situ Measurements of the Thermal Diffusivity: Principle and Experimental Verification

This paper presents an in-situ, non-contact, non-destructive "dual-wavelength laser flash Raman spectroscopy method" for measuring the thermal diffusivity. In this method, a heating pulse is used to heat the sample and another pulsed laser with a different wavelength and negligible heating effect is used as a probe to measure the sample temperature changes during the heating and cooling periods from the Raman peak shifts. The sample temperature rise and fall curves are measured by changing the delay between the heating pulse and the probing pulse with the thermal diffusivity then characterized by fitting the temperature curves. The time delay between the heating and probing pulses can be precisely controlled with a minimum step of 100 ps. Hence, the temperature variation can be scanned with an ultra-high temporal resolution of up to 100 ps, which significantly improves the measurement accuracy of transient thermal parameters. The measurement accuracy of this method has been verified using a bulk material model and experiments. The measured thermal diffusivity of a silicon sample has been obtained to be 8.8×10^(-5 )m^2/s with a 3% difference between the measured value and the average result for bulk silicon in the literature which verifies the reliability and accuracy of this method.

Laser flash photolysis and pulse radiolysis study on chemical activity of VP-16 and podophyllotoxin

Time-resolved laser flash photolysis and pulse radiolysis have been used to study the chemical activity of podophyllotoxin(PPT) and etoposide(VP-16). The mechanism of photoionization of etoposide and podophyllotoxin has been confirmed and illustrated. It is demonstrated that VP-16 and PPT in aqueous solution can be photoionized at 248 nm to give hydrated electron and neutral radical resulting from rapid deprotonation of radical cation of VP-16 and PPT. The quantum yield for the photoionization of VP-16 and PPT with single-photo is 0.21 and 0.61, respectively. In addition, they can react with hydrated electron, hydrogen radical and hydroxyl radical. This will give chemists some advice on synthesizing new derivatives of podophyllotoxin in cancer treatment.

Laser flash photolysis of fullerols of C_(60) and of C_(70) in aqueous solutions

Fullerols of C 60 and of C 70 \ [C 60 (OH)\-\%n\%, C 70 (OH)\-\%m\%], water\|soluble fullerene derivatives, unlike some other fullerene derivatives (such as C 60 (C\-4H\-6O), C 60 (C\-3H\-7N) and C 60 [C(COOEt)\-2]\-\%x\%), do not result in excited triplet state but in ionization via monophotonic process in aqueous solutions with 248 nm laser. The quantum yields of formation of hydrated electron ( Φ e - ) are determined to be 0.08 and 0.11 for fullerols of C 60 and of C 70 respectively at room temperature (ca. 15℃) with KI solution used as reference. By laser flash photolysis and oxidation of sulfate radical anion SO -· \-4, the fullerol radical cation or neutral radical of C 60 is confirmed to be existent and the transient absorption spectra of fullerol radical cation of C 70 are observed for the first time.

NAND Flash存储器单粒子效应试验研究

单粒子效应易诱发空间电子设备发生在轨故障。文章针对大容量NAND Flash存储器,利用皮秒脉冲激光和高能重离子开展了试验研究,明确了此类器件的单粒子效应特点,探索了新型集成电路单粒子效应试验评估方法,为工程设计及试验评估提供了技术基础与保障。经皮秒脉冲激光试验发现,NAND Flash存储器件的存储单元易发生单粒子多位翻转,控制电路单元则发生单粒子锁定和功能中断。经高LET值Xe^+离子辐照试验发现,重离子会诱发器件产生电流尖峰脉冲(或电流火花)现象;在NAND Flash存储器未加电状态下,仍可诱发单粒子翻转;重离子辐照后存储器坏块明显增加,试验获得的单粒子翻转截面高达1. 18×10^-7cm^2/位。基于试验结果分析,认为发生多位翻转的原因是激光束覆盖多个存储单元所造成;重离子辐照引起的浮栅晶体管击穿是存储器坏块增多的原因。

Flash动画在激光课程中的应用意义

激光的发明到现在已经有将近60年了,期间对于激光理论的研究以及技术的应用有了快速的发展,并且对现代人类社会科学技术产生了深刻的影响,传统的教学的方式和推广有很大的局限性,不方便教育者的解说以及学习者的理解。文章分析了"激光原理"课程基于Flash动画制作进行教学改革的意义,并结合"激光原理"课程的特点,提出创新型的教育教学改革方案。

Laser photolysis of ionic liquid [bmim][PF_6]

Photoinduced chemical reactions of 1-butyl-3-methylimidazolium hexafluorophosphate ([bmim][PF_6]) were studied by laser photolysis at a wavelength of 266 nm.Excited triplet state ~3[bmim]^+ was observed,radical cation [bmim]^(2+) and neutral [bmim] radical via photoionization were also formed.Energy transfer from ~3[bmim]^+ toβ-carotene was confirmed.Oxidation via one electron transfer from TMPD to ~3[bmim]^+ was also observed and the rate constant was determined to be 1.2×10.5 L.mol^(-1).s^(-1).The reaction of [bmim][PF_6] with hydrated electron (e_(aq)) was confirmed by laser photolysis in aqueous solution.

基于闪光法的蒸汽发生器传热管导热系数的测量研究

针对蒸汽发生器传热管的导热系数很难由理论计算直接获得、通常需要通过试验测量得到的问题,基于瞬态传热原理,在保持传热管外形的基础上,运用激光闪光法设计了一种基于传热管导热系数测量装置。分别对4种不同厂家制造的690合金传热管的导热系数进行了测量,并将测得的数据在20~400℃范围内进行线性拟合,通过拟合公式,可直接求得该温度范围内任一温度条件下的导热系数,为蒸汽发生器传热计算提供可靠的参数。

2.79μm高速转镜调Q Er,Cr:YSGG纳秒窄脉冲激光器

转镜调Q无插入损耗,是获得窄脉冲、高峰值功率输出激光的直接方式。纳秒脉冲需要使用高速转镜调Q,并精准控制电机转速与氙灯放电延时,以使激光介质上能级粒子数反转最大,获得最大激光能量输出。本文设计了以Arduino mega 2560单片机为核心的高速转镜调Q控制系统,通过精确单片机解析串口屏指令控制激光电源的充放电和高速电机启停,同时通过对转镜脉冲信号整合降频控制氙灯放电时刻,实现对延迟时间的精准控制,实现了灯泵Er,Cr:YSGG激光纳秒窄脉冲调Q输出。在5 Hz重复频率下,转镜转速为650 r/s时,获得的最高单脉冲激光能量为45.7 mJ、脉冲宽度为86.2 ns,相应的峰值功率为530.2 kW。