Density Functional Theoretical Study on SERS Chemical Enhancement Mechanism of 4-Mercaptopyridine Adsorbed on Silver

基于密度泛函理论计算和拉曼光谱理论分析,我们研究了对巯基吡啶(4MPY)分子的拉曼光谱和其在银上的表面增强拉曼光谱(SERS),并进一步探讨了S; ERS与界面吸附结构、异构化、质子化和氢键作用以及低能激发态的关系。首先,我们对两种分子异构体的相对稳定性和拉曼光谱进行了理论分析。在此基础上,; 进而研究了该分子与不同银簇作用时的拉曼光谱,结果表明,4MPY以巯基硫与银簇作用形成强的Ag-; S键,导致拉曼光谱的线型不依赖于所选银簇的大小。接着我们考虑了吡啶氮端作用的两种情况。(1)当4MPY-银簇复合物同时以吡啶氮与水簇或水合质子簇; 形成氢键时,结果表明吡啶环的部分振动频率随氢键和质子化发生蓝移。(2)当考虑吡啶氮与银簇作用时,吡啶环三角畸变振动发生蓝移。上述情况不仅解释了实; 验观测的振动频率变化,而且表明了化学环境改变对相对拉曼强度的影响。最后,我们计算了当对巯基吡啶分子以单端或双端与银簇作用,在考虑激发光与低能激发; 态的能量匹配时,拉曼光谱强度与低能激发态的关系。计算结果表明,在双端吸附构型下,与吡啶氮成键的银簇受激发产生电荷转移态,不仅导致吡啶环v_(12; )、 v_1和v_(8a)振动的拉曼信号增强,而且选择性地增强吡啶环C-H面内对称弯曲振动v_(9a)的拉曼信号。Surface-enhanced Raman spectroscopy (SERS) is one of the most powerful techniques for obtaining fingerprint information on molecules adsorbed on coinage metal surfaces. Its detection sensitivity has reached the single-molecule level. On the basis of density functional theoretical (DFT) calculations and Raman scattering theory, we investigated the normal Raman spectra of two isomers and surface-enhanced Raman scattering (SERS) spectra of 4-mercaptopyridine (4MPY) adsorbed on silver. The results aided us in uncovering the relationships between normal Raman spectra and SERS spectra and adsorption configuration, tautomerization, protonation, and hydrogen bonding interactions as well as low-lying excited states. First, we compared the relative stability and normal Raman spectra of two isomers of 4MPY in the gas phase and aqueous solution with a solvent model similar to the solvation model of density (SMD). We then studied the Raman spectra of 4MPY interacting with silver clusters. Our results indicate that the Raman spectra were not dependent on the size of the silver clusters, owing to the formation of strong Ag-S bonds. We also considered two cases of N-end interaction in the 4MPY-Ag-5 complex. (1) For the hydrogen bond interaction between the nitrogen in 4MPY and water clusters or hydrated proton clusters, the theoretical results indicated that the vibrational frequencies of the pyridine ring increase. (2) For the interaction of the 4MPY-Ag-5 complex with a silver cluster Ag-4 through the lone-paired orbital in nitrogen of the pyridine ring, the theoretical results further revealed that the vibrational frequency shift is in good agreement with SERS peaks reported in the literature. Finally, our calculated results focused on the relationship between the Raman spectra and the charge transfer mechanism when the excitation photonic energy matches the transition energy of low-lying excited states in single-end and double-end adsorption configuration. Particularly for the case of the double-end adsorption configuration, the charge transfer states from the excitation from the silver cluster binding to the pyridine ring not only enhance the Raman signals of v(12), v(1), and v(8a) modes, but also selectively enhance the Raman signal of the v(9a) mode associated with the symmetric C-H in-plane bending vibration.国家自然科学基金（21273182,21533006,21373172）资助项

护士倒班前后智力活动的比较

受试者为20—35岁倒班和正常白班护士共46名。倒班组在上小夜班前和次日大夜班后分别给予一次智力活动测验,正常白班组两次测验的时间和时间间隔与倒班组相同。测验结果表明:倒班组两次测验仅在“数字符号”项目有部分显著性差异;而正常白班第二次测验在“数字符号”和“计数”两个项目,均较第一次测验取得显著进步。这提示倒班对于注意、记忆和反应操作速度可能有些影响

Calculation of passive earth pressures on retaining wall considering soil arching effects of backfill clayey soil

为解释挡土墙后填土被动土压力的非线性分布现象,在考虑土拱形状为圆弧,滑裂面采用朗肯滑裂面的基础上,给出考虑土拱效应的被动土压力系数kAWn,进而基于应力状态法及土楔形体静力平衡两种思想求解了竖向平均应力V？公式,在该基础上,给出黏性土填料下的挡土墙被动土压力分布公式、合力公式及作用点高度计算公式。通过与试验与其他方法对比,文中提出的方法得到验证。最后,研究了黏性土填料下的挡土墙被动土压力变化规律,即考虑土拱效应求得的黏性土填料的被动土压力分布呈现上小下大的指数型分布。此外,随着δ/φ(δ为墙土摩擦角,φ为内摩擦角)的增大,土拱效应逐渐增强,土压力合力点逐渐降低。The nonlinear phenomenon which the passive earth pressure behind the retaining wall of both sand and cohesive soil is nonlinear distribution could be explained by the soil arching effect theory.The formula which calculated passive earth pressure coefficient of which assumed the stress state method and the soil wedge static equilibrium method were derived considering the soil arching effect, assumed arch as circle and the angle of slip surface as Rankine's theory.Then, the distribution of lateral earth pressure considering the soil arching was derived by the above formulations; also the formulas that calculating the magnitude and the point of application of lateral passive earth pressure were derived.The accuracy of proposed method is confirmed by comparing with the experimental tests and values from existing equations.Finally, the trends of distribution and the height of total passive earth pressure of clayey soil are studied; distribution of passive earth pressures considering the soil arching is likely an exponential curve; and the height of resultant earth pressure point is gradually reducing with increasing the ratio of soil-wall friction angle to internal angle δ/φ.国家自然科学基金资助(No.51209180); 浙江省自然科学基金资助(No.Y1091175

Electrochemical and In Situ FTIR Studies of Adsorption and Oxidation of Dimethyl Ether on Platinum Electrode

运用电化学循环伏安法(CV)和原位傅立叶变换红外(FTIR)反射光谱,研究了不同pH值溶液中二甲醚(DME)在Pt电极上的解离吸附和氧化过程.稳态CV结果给出,在0.1mol·L-1H2SO4溶液中,当电位处于0.05-0.35V(vsRHE)区间,约70%的Pt表面位被DME的解离吸附产物占据.DME电氧化反应的活性随pH值增加而下降,在0.1mol·L-1NaOH溶液中,氢的吸脱附几乎不受抑制且观察不到明显的氧化电流,表明DME醚键上氧原子的质子化是其发生解离吸附和氧化的必要条件.原位FTIR光谱研究给出DME解离吸附和氧化过程的分子水平信息,指出DME在低电位区间解离生成线型吸附态CO(COL)毒性中间体.当电位高于0.55V(vsRHE)时,COL开始氧化为CO2;在0.75-1.00V(vsRHE)的电位区间则可同时发生经活性中间体(HCOOH)的氧化过程.Dissociative adsorption and electrooxidation of dimethyl ether (DME) on a platinum electrode in different pH solutions were studied using cyclic voltammetry (CV) and in situ FTIR reflection spectroscopy. The coverage of the dissociative adsorbed species was measured about 70% from hydrogen adsorption-desorption region (0.05-0.35 V(vs RHE)) of steady-state voltammogram recorded in 0.1 mol·L-1 H2SO4 solution. It was found that the electrochemical reactivity of DME was pH dependent, i.e., the larger the pH value was, the less the reactivity of DME would be. No perceptible reactivity of DME in 0.1 mol·L-1 NaOH solution could be detected. It was revealed that the protonation of the oxygen atom in the C-O-C bond played a key role in the electrooxidation of DME. In situ FTIR spectroscopic results illustrated that linearly bonded CO (COL) species determined at low potential region were derived from the dissociative adsorption of DME and behaved as 'poisoning' intermediate. The COL species could be oxidized to CO2 at potential higher than 0.55 V (vs RHE), and in the potential range from 0.75 to 1.00 V (vs RHE) DME was oxidized simultaneously via HCOOH species that were identified as the reactive intermediates.国家自然科学基金(20433060,20673091)资助项

高寒草甸地区牧草生长量模拟模式研究

本文讨论了土壤含水量和蒸散量对牧草生长量的影响过程，提出牧草干物质增长模式，并根据青海海北高寒草甸地区的气象条件，对牧草生长量模式进行数值模拟，同时，与实测值进行比较，模拟结果与实测值趋向一致，可为牧草产草量预报提供一定实用价值和科学依据

金电极上偶氮腺嘌呤的电化学行为研究

本文研究了光滑金电极上偶氮腺嘌呤的电化学特性,并确定了相关动力学参数.在含偶氮腺嘌呤的0.2mol·L-1的磷酸盐缓冲液（PBS,pH=4.0～10.0）中,发现其循环伏安图上出现一对氧化还原峰.基于对扫速和伏安峰值电位的分析,结果表明这是一个由吸附控制的可逆偶氮腺嘌呤氧化还原电化学过程.当pH值从低到高改变时,氧化还原峰值向负电位移动,证实H+参与了该反应.通过进一步实验数据分析和电极表面吸附量计算,发现该反应为分步进行的两电子两质子反应.最后,通过快速循环伏安扫描方法确定了电化学过程的表观传递系数α和表观速率常数ks

Electrochemical and In Situ FTIR Studies of Adsorption and Oxidation of Dimethyl Ether on Platinum Electrode

Dissociative adsorption and electrooxidation of dimethyl ether (DME) on a platinum electrode in different pH solutions were studied using cyclic voltammetry (CV) and in situ FTIR reflection spectroscopy. The coverage of the dissociative adsorbed species was measured about 70% from hydrogen adsorption-desorption region (0.05-0.35 V(vs RHE)) of steady-state voltammogram recorded in 0.1 mol center dot L-1 H2SO4 solution. It was found that the electrochemical reactivity of DME was pH dependent, i.e., the larger the pH value was, the less the reactivity of DME would be. No perceptible reactivity of DME in 0.1 mol center dot L-1 NaOH solution could be detected. It was revealed that the protonation of the oxygen atom in the C-O-C bond played a key role in the electrooxidation of DME. In situ FTIR spectroscopic results illustrated that linearly bonded CO (COL) species determined at low potential region were derived from the dissociative adsorption of DME and behaved as 'poisoning' intermediate. The COL species could be oxidized to CO2 at potential higher than 0.55 V (vs RHE), and in the potential range from 0.75 to 1.00 V (vs RHE) DME was oxidized simultaneously via HCOOH species that were identified as the reactive intermediates