等离激元催化反应动力学研究装置

等离激元催化是利用金属纳米颗粒的局域表面等离激元来驱动化学反应的现象,已经发展成为多相催化的一个新兴研究领域.然而,实验研究中温度测量不准和反应物吸附状态不明确导致等离激元催化反应的微观机制存在争议.为了研究等离激元催化反应动力学,本文设计搭建了一台基于在线质谱检测的装置,通过对反应器的改进来解决温度测量和吸附状态识别的问题.相比于传统设计中仅安装一个热偶,本文在反应器中安装了三个热偶.基于传热模型,这种多点测温技术可以定量计算出催化剂的有效温度以及热反应的贡献.此外,在装置中集成了程序升温脱附谱,用于测量反应物的吸附状态.通过对模型催化反应Au/TiO_(2)等离激元催化H_(2)+D_(2)→HD的定量测量,测试了该装置的性能,明确了H_(2)/D_(2)在Au/TiO_(2)界面的解离吸附和非热反应对HD生成的贡献,证明了该装置在等离激元催化反应动力学研究方面的能力.

兼具小气载吸附、快速换样和全面温控的程序升温脱附谱装置

程序升温脱附谱技术能定量识别表面物种和测量脱附动力学,因此被广泛应用于多相催化和表面科学研究.对于高效率和高质量的程序升温脱附谱实验而言,减小吸附过程中的气载并在不破坏超高真空条件下完成样品更换以及实现对样品全方位的温度控制是至关重要的.然而,现有的表面科学程序升温脱附谱装置通常无法同时满足这些条件。鉴于此,本文搭建了一台可实现小气载进样、快速换样以及全面温控的程序升温脱附谱装置。使用自动控制的基于微毛细管阵列的溢流分子束给样器,制备分子吸附的表面,让气体的进样更加精准并大幅减小了气载。借助液氮传输线并优化样品台处的热接触和热偶连接方式,使得这台程序升温脱附谱装置同时具备了快速换样、精准测温、快速降温以及稳定线性升温等功能。通过测量水从高定向热解石墨和TiO_(2)(110)表面的脱附特征以及甲氧基阴离子在TiO_(2)(110)表面的光催化氧化反应,证实了该程序升温脱附谱装置在测量脱附动力学参数、定量识别表面吸附物种和吸附位点以及分析表面光化学反应等方面的性能,本工作将为研究人员设计高效率和高质量的程序升温脱附谱装置提供宝贵的经验和思路。

使用石英手性项进行归一化的宽带红外和频振动光谱方法的验证

和频振动光谱已被广泛用于表征各种界面、然而,对于某些界面。如担载粉末颗粒的界面,由于粉末会散射和频振动光谱信号使得光谱难以准确测量,获取高信噪比的和频振动光谱信号成为了一个巨大的挑战.本文发展了一种新的方法,在和频振动测量时,使用一片z切的α-石英晶体作为基底,担载少量催化剂粉末样品.该方法不仅可以通过石英晶体非共振电场的干涉放大界面颗粒上吸附分子的和频振动信号,并获得相位信息,还可以用于宽带红外和频振动光谱进行归一化.通过分离不同偏振的和频振动信号,能够分离并同时收集手性和非手性的和频振动信号.使用手性的和频振动信号来归一化非手性的和频振动强度,从而避免因担载物质到石英晶体上或由于不同时刻光的不稳定性引起的界面变化或者光重合差异.本文通过测量担载有MoC纳米粒子的石英基底上CH3OD的吸附来验证了本文的方法.无论界面情况如何,都能获得高信噪比的和频振动光谱.

窄脉冲分子束系统的发展与表征

本文结合高速分子斩波器与温度可调的脉冲阀,搭建了一套制备脉冲宽度窄且速度连续可调的分子束装置.通过共振增强多光子电离方法对分子束的脉冲宽度与速度进行了表征.测量表明斩波器可将氢气分子束在脉冲阀下游约193 mm处的脉冲宽度从20.0μs缩短到6.3 us.为了精确测量氢气分子的速度,实验采用了受激拉曼泵浦和共振增强多光子电离结合的泵浦-探测方法,利用纳秒级的受激拉曼泵浦脉冲激光作为测量时间零点,在标记分子飞行固定距离(193 mm)后精确测量分子到达时间以获得分子束速度同时通过改变脉冲阀的温度,实现氢气分子束速度在1290~3550 m/s之间的连续调节.本文搭建的系统在化学反应动力学领域有多种潜在应用,包括与离子阱以及分子束表面散射装置结合进行实验研究.

阿尔法蒎烯臭氧分解反应的极紫外自山电子激光光电离质谱研究

阿尔法蒎烯是大气中含量最高的自然源萜类挥发性有机物,其臭氧化分解反应会产生大量的反应中间体和产物,精确表征这些物种被认为是大气化学最前沿、最具挑战性的课题之一.本文利用极紫外自由电子激光光电离质谱方法,研究了阿尔法蒎烯的臭氧分解反应机理.该反应是在2立方米的烟雾箱中进行,利用气动透镜把产生的气溶胶传输到质谱探测腔室,利用极紫外自山电子激光对气溶胶进行单光子软电离,测得了常规实验方法难以得到的飞行时间质谱,发现了一系列新物种.与量子化学理论计算相结合,揭示了这些新物种的反应机理.这些研究结果从分子水平上揭示了蒎烯的臭氧分解反应机制,有助于理解大气雾霾微观机理.

OCS分子在里德堡F态的真空紫外光解动力学:S(^(3)P_(J=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(^(3)P_(J=2,1,0))产物的离子影像,从中发现了两个解离通道:S(^(3)P_(J=2,1,0))+CO(X^(1)∑+)和S(^(3)PJ=2,1,0)+CO(A^(3)Π),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(^(3)P_(J=2,1,0))+CO(X^(1)∑^(+))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(^(3)P_(2))、S(^(3)P_(J))和S(^(3)P_(0))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共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.

Direct experimental detection of hydrogen radicals in non-oxidative methane catalytic reaction

Non-oxidative conversion of methane to olefins,aromatics and hydrogen(MTOAH) has been reported recently over metal single sites such as iron and platinum.The reaction was proposed to involve catalytic activation of methane followed by gas phase C-C coupling of methyl radicals.This study using H atom Rydberg Tagging time-of-flight technique provides direct experimental evidence for the formation of hydrogen radicals during MTOAH reaction over a catalytic quartz wall reactor containing embedded iron species(denoted as Fe-reactor).Fe-reactor gives 7.3% methane conversion at 1273 K with 41.2% selectivity toward C2(ethane,ethylene and acetylene) and 31.8% toward BTX(benzene,toluene and xylene),respectively.The enhancing effects of hydrogen radicals on overall MTOAH performance are validated by cofeeding hydrogen donor benzene,which provides an additional route of methane activation apart from catalytic activation.

Genetic Analysis of Grain Yield in a 7×7 Diallel Cross F_2 Population of Wheat(T.Aestivum L.)

In order to obtain genetic information for grain yield, seven genetically diverse wheat cultivars were crossed in an incomplete diallel to study the inheritance of grain yield using F_2 progenies for two years. Significant differences were observed among genotype, year and genotype × year interaction for grain yield, and both general combining ability(GCA) and specific combining ability(SCA) were also highly significant for grain yield, suggesting that the trait was controlled by both additive and non-additive effect. The GCA estimates revealed that the best combiners for grain yield were Yangmai 5 and Ningmai 9. Adequacy tests revealed that data of grain yield was fully adequate for genetic interpretation. Over-dominance genetic effects were important for the expression of grain yield. Grain yield exhibited moderately high value of narrow sense heritability(h_N^2=66.98% and h_N^2=72.37%).

Changes of Rubisco in Flag Leaves of Wheat with Different Quality Types during Grain Filling Stage

[ Objective] In this study, the formation mechanism of grain quality of soft wheat was investigated to provide support for soft wheat breeding. [ Meth- od] Using soft and hard wheat varieties as experimental materials, changes of Rubisco （ribulose-1,5-bisphosphate carboxylase/oxygenase） degradation in flag leav- es with different quality types during grain fillLing stage were investigated. [ Result] Chlorophyll content and Rubisco content were both gradually reduced in flag leaves of wheat cultivars with different quality types during grain filling stage. Changes of Rubisco content were insignificant at early grain firing stage, but Rubisco content in flag leaves of soft wheat was higher than that of hard wheat at mid-late grain filling stage. Degradation products of Rubisco large subunits with molecular weight of 51 kD could be detected in flag leaves of various wheat cultivars. Rubisco in flag leaves of hard wheat Zheng 9023 was significantly earlier degraded com- pared with Yangnmi 15, indicating that leaf senescence in hard wheat was earlier than soft wheat, which suggested that the protein accumulation in wheat grains may be related with Rubisco degradation in flag leaves after anthesis. [ Conclusion] This study implied the foundation of soft wheat breeding and optimization of cultiva- tion and wheat management in the field.

Effects of NO_(2) and SO_(2) on the secondary organic aerosol formation fromβ-pinene photooxidation

Elucidating the effects of anthropogenic pollutants on the photooxidation of biogenic volatile organic compounds is crucial to understanding the fundamental mechanisms of secondary organic aerosol(SOA)formation.Here,the impacts of NO_(2)and SO_(2)on SOA formation from the photooxidation of a representative monoterpene,β-pinene,were investigated by a number of laboratory studies.The results indicated NO_(2)enhanced the SOA mass concentrations and particle number concentrations under both low and highβ-pinene conditions.This could be rationalized that the increased O_(3)concentrations upon the NO_(x)photolysis was helpful for the generation of more amounts of O_(3)-oxidized products,which accelerated the SOA nucleation and growth.Combing with NO_(2),the promotion of the SOA yield by SO_(2)was mainly reflected in the increase of mass concentration,which might be due to the elimination of the newly formed particles by the initially formed particles.The observed low oxidation degree of SOA might be attributed to the fast growth of SOA,resulting in the uptake of less oxygenated gas-phase species onto the particle phase.The present findings have important implications for SOA formation affected by anthropogenic–biogenic interactions in the ambient atmosphere.

Diffusion effect on the decay of time-resolved photoluminescence under low illumination in lead halide perovskites

Time-resolved photoluminescence(TRPL)has been extensively used to measure the carrier lifetime in lead halide perovskites.The TRPL curves of perovskite materials are usually fitted with a multi-exponential function,instead of a single exponential one.This was considered to be a result of the surface and the bulk recombination or the additional radiative recombination caused by the high excited carrier density.Here,a new model considering the diffusion and the trap-assisted recombination of carriers is proposed to explain the TRPL curves.The expressions of the TRPL curves and the transient absorption(TA)dynamic curves are theoretically derived,demonstrating that the TRPL curve is an infinite exponential series,regardless of the presence of surface recombination or not.Our newly developed highly sensitive nanosecond TA and TRPL were employed to measure the carrier dynamics of the same sample under low illumination in the linear response region of TA,thereby experimentally verifying our model.These results suggest that the decay of the TRPL is not only a consequence of the carrier recombination but also the carrier diffusion.TRPL cannot provide a direct measurement of the carrier lifetime,whereas TA spectroscopy can.Furthermore,the surface and the bulk recombination can be resolved and the average diffusion coefficient(D)can also be correctly obtained by combining TRPL and TA measurements.We also propose an approximate method for calculating the carrier lifetime and diffusion coefficient of high-quality perovskite films.Our model provides not only a new interpretation of the dynamics of the PL decay but also a deep insight into the carrier dynamics in the nanosecond time scale under working condition of perovskites solar cells.

Breaking Mirror Circularly Polarized Luminescence of Chiral Metal-Organic Frameworks by High-Pressure Stimulation

Understanding high-pressure-stimulated circularly polarized luminescence(CPL)of enantiomers remains a challenging but significant task in fundamental research and optical applications.Here,we combined in situ high-pressure photoluminescence with circularly polarized light to study how high pressure stimulated the CPL of crystalline enantiomers.Chiral lanthanide(Ln)-tartrate(Tar)metal-organic frameworks(MOFs;Ln=Eu,Tb)were synthesized to study their CPL from atmospheric pressure to 10 GPa.Under atmospheric pressure,D-and L-Eu(Tar)showed strong andmirror CPL.CPL intensity changes,emission wavelength shifts,and signal inversions were induced by increasing pressure.Note that the D-Eu(Tar)enantiomer showed strong CPL with a maximal dissymmetric factor(g_(lum))of 0.69 under 3 GPa,which is much higher than that under atmospheric pressure and of other reported MOF-based CPL materials.More interestingly,D-and L-Ln(Tar)enantiomers display obvious asymmetric CPL signals with increasing pressure,demonstrating that high pressure can break the mirror CPL of the MOF enantiomers.Our findings provide a critical understanding on in situ high-pressure CPL of chiral materials and establish a new optical phenomenon where high pressure can break the mirror CPL of enantiomers.

Clinical curative effect of fuzi-cake-separated moxibustion for preventing dysuria after operation for lower limb fracture

OBJECTIVE: To assess the clinical curative effect of fuzi-cake-separated moxibustion at Zhongji(CV 3)and Guanyuan(CV 4) for preventing dysuria after internal fixation of lower limb fractures.METHODS: Sixty patients conforming to the inclusion standards were randomly divided into a treatment group(n=30) and a control group(n=30).Fuzi-cake-separated moxibustion was performed at Guanyuan(CV 4) and Zhongji(CV 3), 20 min at a time, twice a day, for 3 days before operation in the treatment group. No fuzi-cake-separated moxibustion was performed in the control group. After treatment, the score for symptoms of first urination, urinary time, urinary volume, 24 h remaining urinary volume, incidence of uroschesis, and rate of controlling dysuria were compared to evaluate the curative effect of preventing post-operative dysuria.RESULTS: The score for symptoms of first urination,24 h remaining urinary volume(maximum 120 m L vs 250 m L, and less than 10 m L in 24 cases vs 15 cases), and the rate of controlling dysuria(83.34% vs30%) were significantly better(P<0.05, P<0.05, and P<0.001, respectively) in the treatment compared with the control group. There was no statistical difference(P>0.05) between the two groups in first post-operative urinary time, urinary volume, or incidence of 24 h uroschesis.CONCLUSION: Fuzi-cake-separated moxibustion at Zhongji(CV 3) and Guanyuan(CV 4) can better prevent post-operative dysuria, effectively promote the functional restoration of the urinary bladder,and control the incidence of post-operative dysuria.

In-situ generation and global property profiling of metal nanoclusters by ultraviolet laser dissociation-mass spectrometry

Metal nanoclusters are promising nanomaterials with unique properties, but only a few ones with specific numbers of metal atoms can be obtained and studied up to now. In this study, we establish a new paradigm of in-situ generation and global study of metal nanoclusters with different sizes, constitutions, and charge states, including both accurate constitution characterization and global activity profiling. The complex mixtures of metal nanoclusters are produced by employing single-pulsed 193-nm laser dissociation of monolayer-protected cluster(MPC) precursors within a high-resolution mass spectrometry(HRMS). More than400 types of bare gold nanoclusters including novel multiply charged(2+ and 3+), S-/P-doped, and silver alloy ones can be efficiently generated and accurately characterized. A distinct size(1 to 142 atoms)-and charge(1+ to 3+)-hierarchy reactivity is clearly observed for the first time. This global cluster study might greatly promote the developments and applications of novel metal nanoclusters.

Elucidating the various multi-phosphorylation statuses of protein functional regions by 193-nm ultraviolet photodissociation

Ultraviolet photodissociation is a high-energy fast excitation method in mass spectrometry and has beensuccessfully applied for the elucidation of sequences and structures of biomolecules. However, its abilityto distinguish the phosphorylation sites isomers of multi-phosphopeptides has been not systematicallyinvestigated until now. A 193-nm ultraviolet laser dissociation mass spectrometry system wasestablished in this study and applied to elucidate the complex multi-phosphorylation statuses mimickingthe functional regions of Sicl, Gli3 and Tau. The numbers of matched fragment ions and phosphorylationsite-determining ions were improved on average 123% and 104%, respectively, by utilizing the ultravioletphotodissociation strategy, comparing to the typically utilized collision induced dissociation strategy.Finally. 94% phosphorylation sites within various statuses were unambiguously elucidated.

Chemical and spectroscopic characteristics of humic acid from a clay loam soil in Ontario after 52 years of consistent fertilization and crop rotation

Long-term fertilization and crop rotation can influence both organic C sequestration as well as the C composition of soils and the more resistant organic C compounds contained in humic acid(HA). This study examined the effects of fertilization and cropping type(monoculture corn(MC) and Kentucky bluegrass sod(KBS) and corn-oat-alfalfa-alfalfa rotation(RC)) on the HA composition of soil from a 52-year field study in southern Ontario, Canada. Humic acid samples were extracted from soil, and elemental analysis, infrared spectroscopy, solid state 13C nuclear magnetic resonance spectra, and electron paramagnetic resonance methods were used to determine the influence of the cropping type on the characteristics of HA. Both fertilization and cropping type affected the chemical characteristics of HA. Fertilization led to a 5.9% increase in C, a 7.6% decrease in O, and lower O/C and(N + O)/C ratios in HA as compared to the corresponding non-fertilized treatments. Rotation resulted in a lower proportion of C(48.1%) and a greater(N + O)/C ratio(0.7) relative to monoculture cropping. Infrared spectroscopy analysis showed that HA contained more C-O groups in fertilized soil than in non-fertilized soil under MC and KBS. Fertilization increased the O-alkyl-C, phenolic-C, and free radical contents of HA relative to non-fertilization treatments. Rotation decreased the aliphatic and carboxyl groups and increased the O-alkyl, carbohydrate, aryl, and phenolic groups and free radicals, relative to MC and KBS. Both long-term crop rotation and fertilization dramatically modified the soil HA composition. Significant relationships were observed between the molecular composition of HA and soil organic C. Hence, humic acid characterization could be used as an indicator of the long-term sustainability of crop management practices.

Deconstructing Vibrational Motions on the Potential Energy Surfaces of Hydrogen-Bonded Complexes

Internal vibrations underlie transient structure formation,spectroscopy,and dynamics.However,at least two challenges exist when aiming to elucidate the contributions of vibrational motions on the potential energy surfaces.One is the acquisition of well-resolved experimental infrared spectra,and the other is the development of efficient theoretical methodologies that reliably predict band positions,relative intensities,and substructures.Here,we report size-specific infrared spectra of ammonia clusters to address these two challenges.Unprecedented agreement between experiment and state-of-the-art quantum simulations reveals that the vibrational spectra are mainly contributed by proton-donor ammonia.A striking Fermi resonance observed at approximately 3210 and 3250 cm^(−1)originates from the coupling of NH symmetric stretch fundamentals with overtones of free and hydrogen-bonded NH bending,respectively.These novel,intriguing findings contribute to a better understanding of vibrational motions in a large variety of hydrogen-bonded complexes with orders of magnitude improvements in spectral resolution,efficiency,and specificity.

Epitaxy of rare earth element fluorcarbonate minerals from carbonatite dyke at Bayan Obo, Inner Mongolia, China

Rare earth element fluorocarbonate minerals such as bastnaesite and parisite are firstly discovered in carbonatite dykes from Bayan Obo, Inner Mongolia, China. Bastnaesite rarely occurs as homogeneously single crystal, but contains microfine phase of parisite. They form regular intergrowth along (0001) plane net, which is identified as epitaxy. This eptactic texture results from the variation of chemical composition of crystallizing agents of those minerals that crystallize directly from carbonatite magma.