金纳米粒子组装体系中偶联单分子层膜结构的SERS光谱表征与分析

通过分子自组装方法制备4,4′-二硫联吡啶(PySSPy)单分子膜修饰的金电极. 利用所形成的对巯基吡啶自组装单分子膜(SAMs)作为偶联层进行金纳米粒子有序膜的组装. 对该纳米粒子组装体系进行Raman光谱测定, 得到了具有良好信噪比的对巯基吡啶单分子膜的表面增强拉曼散射(SERS)光谱. 在此基础上, 进一步采用电化学现场SERS光谱技术研究了该纳米粒子组装体系的SERS光谱随电位变化的规律. 在该体系稳定的电位范围内表征对巯基吡啶单分子膜的特征谱峰1011与1093 cm^-1、1575与1610 cm^-1以及1206与1215 cm^-1这三对谱峰其强度随着所施加电位的改变呈现出明显的规律性. 分析表明, 偶联单分子层中吡啶环芳香性随着所施加电位的改变而有规律地变化是SERS光谱特征改变的内在原因.     

高浓度LiClO4/丙酮溶液中离子-溶剂和离子-离子的相互作用

利用红外和拉曼光谱技术研究了不同浓度LiClO₄/丙酮溶液中离子-溶剂和离子-离子的相互作用. 红外和拉曼光谱的分析表明, Li^＋与丙酮分子发生了强烈的相互作用, 导致丙酮C—C伸缩振动谱带、C＝O伸缩振动谱带等发生了分裂. Li^＋的溶剂化数随溶液浓度的增加逐渐降低, 在所研究的LiClO₄浓度范围(0.31～3.98 mol•kg^－1)内由3.4减小到1.9. 此外, 根据的谱带变化确定了溶液中存在的多种离子对的形式, 计算了缔合平衡常数, 并与电导实验结果进行了比较, 解释了这两种方法测定的离子缔合常数存在差异的主要原因.     

高浓度LiClO4/丙酮溶液中离子-溶剂和离子-离子的相互作用

利用红外和拉曼光谱技术研究了不同浓度LiClO₄/丙酮溶液中离子-溶剂和离子-离子的相互作用. 红外和拉曼光谱的分析表明, Li^＋与丙酮分子发生了强烈的相互作用, 导致丙酮C—C伸缩振动谱带、C＝O伸缩振动谱带等发生了分裂. Li^＋的溶剂化数随溶液浓度的增加逐渐降低, 在所研究的LiClO₄浓度范围(0.31～3.98 mol•kg^－1)内由3.4减小到1.9. 此外, 根据的谱带变化确定了溶液中存在的多种离子对的形式, 计算了缔合平衡常数, 并与电导实验结果进行了比较, 解释了这两种方法测定的离子缔合常数存在差异的主要原因.     

氨和有机胺对羰基硫与α-Fe2O3非均相反应的影响

利用原位漫反射傅里叶红外光谱(DRIFTS), 考察了室温下羰基硫(COS)在经氨气和有机胺预吸附的α-Fe₂O₃上的非均相反应, 并同时比较了氨气和不同有机胺(甲胺、三甲胺、三乙胺、苯胺、吡啶和吡咯)对反应活性的影响及其反应动力学. 结果表明, 经碱性物质预吸附后, COS可在α-Fe₂O₃表面发生氧化反应, 主要产物为气态CO₂、表面HCO₃^-、表面CO₃^2-和表面SO₄^2-, 且α-Fe₂O₃表面预吸附的碱性物质大大提高了COS在α-Fe₂O₃上的反应能力, 在碱性物质的影响中, 甲胺对反应的促进能力最大, 相比纯α-Fe₂O₃反应的反应活性提高了约4.5倍, 然而苯胺和吡咯对COS的反应影响不是很明显.观察到的不同碱性物质对COS的转化能力依次为: 甲胺>三甲胺>氨气>三乙胺>吡啶>吡咯>苯胺≈纯样品, 受碱性物质的影响, COS的反应级数由一级转变为二级. 此外, 研究也发现碱性物质的覆盖度和表面吸附水对COS转化能力存在一定的影响. 这些实验结果表明在碱性物质存在下,表面M―O^-是COS在α-Fe₂O₃发生氧化反应的关键活性位点, 对反应活性的贡献较大, 并在此基础上探讨碱性条件下COS的反应转化机制.     

Li＋在基于N,N-二甲基甲酰胺混合溶剂中的溶剂化

利用红外和拉曼光谱技术研究了Li^＋在不同浓度、不同溶剂组成的LiBF₄/N,N-二甲基甲酰胺-乙腈、LiBF₄/N,N-二甲基甲酰胺-四氢呋喃电解质溶液中的优先溶剂化现象. 红外和拉曼光谱的分析表明, Li^＋主要与DMF分子相互作用, 导致该分子的C＝O伸缩振动谱带、N—C＝O形变谱带、CH₃摇摆谱带等发生了分裂. Li^＋与其它溶剂分子的相互作用较弱, 谱带的分裂现象并不明显. Li^＋溶剂化数的计算显示, Li^＋第一溶剂化层内DMF分子的数目一般大于2, 这说明 Li^＋在混合溶剂体系内优先与DMF分子相互作用. 量子化学计算支持了这一结论.     

Li＋在基于N,N-二甲基甲酰胺混合溶剂中的溶剂化

利用红外和拉曼光谱技术研究了Li^＋在不同浓度、不同溶剂组成的LiBF₄/N,N-二甲基甲酰胺-乙腈、LiBF₄/N,N-二甲基甲酰胺-四氢呋喃电解质溶液中的优先溶剂化现象. 红外和拉曼光谱的分析表明, Li^＋主要与DMF分子相互作用, 导致该分子的C＝O伸缩振动谱带、N—C＝O形变谱带、CH₃摇摆谱带等发生了分裂. Li^＋与其它溶剂分子的相互作用较弱, 谱带的分裂现象并不明显. Li^＋溶剂化数的计算显示, Li^＋第一溶剂化层内DMF分子的数目一般大于2, 这说明 Li^＋在混合溶剂体系内优先与DMF分子相互作用. 量子化学计算支持了这一结论.     

异烟酸在碱性溶液中金电极上的现场表面增强振动光谱研究

应用表面增强红外吸收光谱法、循环伏安法和微分电容法研究了0.1 mol•L^－1 KClO₄和0.1 mol•L^－1 KCl碱性化溶液(pH 10)中, 异烟酸(INA)在Au电极表面的吸附取向和结构. 结果表明: －0.5～0.2 V (vs. SCE)间INA阴离子(INA^－)通过其羧酸根上的两个氧原子垂直吸附在Au电极表面; 特性吸附Cl^－对上述吸附结构无实质影响. 进一步的表面增强拉曼光谱的测试表明即使在－0.8～－0.5 V, 极少量吸附的INA^－很可能仍维持上述基本构型.     

黄曲霉素B1在银团簇表面吸附的表面增强拉曼光谱

采用密度泛函理论(DFT)的B3LYP方法和6-311g(d, p)(C, H, O)/LanL2DZ(Ag)基组, 优化得到黄曲霉素分子AFB₁与Ag小团簇形成的复合物AFB₁-Ag_n (n=2, 4, 6)的稳定结构, 并计算了三种复合物的表面增强拉曼光谱(SERS)和预共振拉曼光谱(SERRS), 与实验结果相一致. 计算结果显示: 三种复合物表面增强拉曼光谱中C＝O伸缩振动模的增强因子约为10²-10³, 是由于极化率改变引起的静化学增强. 根据含时密度泛函理论(TDDFT)方法计算得到的吸收光谱, 分别选择407.5、446.2和411.2 nm作为入射光, 计算三种复合物的共振拉曼光谱, 发现在SERRS光谱中, Ag―O伸缩振动的增强因子达到10⁴量级, 主要是由电荷转移产生的共振增强引起的.     

黄曲霉素B2分子吸附在银团簇的表面增强拉曼散射机理

采用密度泛函理论（DFT）B3LYP方法,6-311G（d,p）（C,H,O）/LANL2DZ（Ag）基组,计算了黄曲霉素B₂（AFB₂）分子吸附在Ag₂团簇的表面增强拉曼散射（SERS）光谱和预共振拉曼光谱,并与实验结果比较. 结果显示：AFB₂分子在基态Ag₂团簇表面吸附时,增强因子最大达到10²,对应吡喃（pyrane）环C=O伸缩振动,主要是由AFB₂分子周围化学环境改变而引起的基态静极化率改变导致的化学增强. 不同激发波长下的AFB₂分子预共振拉曼光谱的增强强度不同：电荷转移态激发波长为1144 和544 nm时拉曼信号增强了10²倍,而选择电荷转移预共振波长432和410 nm作为入射光时,其拉曼信号增强了10⁴倍,增强机理为银团簇和黄曲霉素分子之间的电荷转移共振增强. 因此通过改变入射光波长,选择电荷转移共振激发波长,更有利于强致癌物AFB₂分子的痕量检测.     

吡啶基团的对称性和离子化对分子双光子吸收截面的影响

采用超快速激光光谱方法研究了含吡啶基团的四个联苯乙烯衍生物及两个杂环分子(A: 4,4’-二(2-(4-吡啶基)乙烯)联苯; B: 4,4’-二(2-(2-吡啶基)乙烯)联苯; C: 1-甲基-4-(2-(4’-(2-(4-吡啶基)乙烯基)-4-联苯)乙烯基)吡啶碘盐; D: 1-甲基-2-(2-(4’-(2-(2-吡啶基)乙烯基)-4-联苯)乙烯基)吡啶碘盐; E: 4-(2-(9-丁基-9氢-3-咔唑)乙烯基)-1-甲基吡啶碘盐; F: 4-(2-(9-丁基-9氢-3-咔唑)乙烯基)-1-甲基喹啉碘盐)的结构-性能关系. 实验结果显示双光子吸收截面最大的是分子E, 高达617.3 GM; 最小的是分子B, 为19.3 GM(1 GM=10^-50 cm⁴·s·photon^-1). 实验研究结果表明, 分子中吡啶基团的对称性及其离子化对分子双光子吸收截面起很重要的作用; 进一步用理论计算证实了以上实验结论并对其机制进行了分析讨论.     

Theoretical study of vibration spectra of sensitizing dyes for photoelectrical converters based on ruthenium(II) and iridium(III) complexes

Quantum-chemical method of the density functional theory was employed to calculate, with the use of a B3LYP hybrid exchange-correlation functional, the IR absorption and Raman spectra of [Ru(bpy)₂(CN)₂] and [Ir(bpy)₂(CN)₂]⁺ complexes. All the normal vibrational frequencies were analyzed and new assignments of a number of bands in the IR absorption and Raman spectra were made. The role of vibrational motions of metal atoms and ligands in the vibronic deformation of electron shells in the course of electron transfer was discussed. This was done using data on surface-enhanced Raman spectra of [Fe(bpy)₂(CN)₂] and [Ru(bpy)₃]²⁺ complexes adsorbed on the surface of colloid silver.     

IR and Raman Vibrational Assignments for Metal-free Phthalocyanine from Density Functional B3LYP／6-31G（d） Method

Vibrational (IR and Raman) spectra for the metal-free phthalocyanine (H2Pc) have been comparatively investigated through experimental and theoretical methods. The frequencies and intensities were calculated at density functional B3LYP level using the 6-3 IG(d) basis set. The calculated vibrational frequencies were scaled by the factor 0.9613 and compared with the experimental result. In the IR spectrum, the characteristic IR band at 1008.cm^-1 is interpreted as C-N (pyrrole) in-plane bending vibration, in contrast with the traditional assigned N-H in-plane or out-of-plane bending vibration. The band at 874 cm^-1 is attributed to the isoindole deformation and aza vibration. In the Raman spectrum, the bands at 540, 566, 1310, 1340, 1425, 1448 and 1618 cm^-1 are also re-interpreted. Assignments of vibrational bands in the IR and Raman spectra are given based on density functional calculations for the first time. The present work provides valuable information to the traditional empirical assignment and will be helpful for further investigation of the vibration spectra of phthalocyanine analogues and their metal complexes.     

Infrared Spectroscopic Studies on the Surface Chemistry of High‐Surface‐Area Gallia Polymorphs

Polymorphs α, β, and γ of Ga₂O₃ having hexagonal (corundum‐type), monoclinic and cubic (spinel‐type) structure, respectively, were prepared in a high‐surface‐area form, and characterized by powder X‐ray diffraction. Nitrogen adsorption at 77 K showed these gallia samples to have specific surface areas of 77 (α‐Ga₂O₃), 40 (β‐Ga₂O₃) and 120 m² g^?1 (γ‐Ga₂O₃). Fourier transform infrared spectroscopy of adsorbed carbon monoxide (at 77 K) and pyridine (at room temperature) showed that the three gallia polymorphs have a very similar surface Lewis acidity, regardless of their different crystal structures. This Lewis acidity was assigned, mainly, to coordinatively unsaturated tetrahedral Ga³⁺ ions situated on the surface of the small crystallites which constitute the different metal oxide varieties. Ga³⁺···CO adducts formed after CO adsorption gave (in all cases) a characteristic C–O stretching band at 2195–2200 cm^?1, while Lewis‐type adducts formed with adsorbed pyridine were characterized by IR absorption bands at 1610–1612 and 1446–1450 cm^?1. The three (partially hydroxylated) gallia polymorphs showed also a very weak Brønsted acidity, which they manifested by forming hydrogen‐bonded adducts with both CO and pyridine; however no protonation of adsorbed pyridine occurred.     

A discrete interaction model/quantum mechanical method for simulating surface-enhanced Raman spectroscopy

We have derived and implemented analytical gradients for the discrete interaction model/quantum mechanics (DIM/QM) method. DIM/QM combines an atomistic electrodynamics model with time-dependent density functional theory and thus enables modeling of the optical properties for a molecule while taking into account the local environment of a nanoparticle's surface. The DIM/QM analytical gradients allow for geometry optimizations, vibrational frequencies, and Raman spectra to be simulated for molecules interacting with metal nanoparticles. We have simulated the surface-enhanced Raman scattering (SERS) spectra for pyridine adsorbed on different sites of icosahedral nanoparticles with diameters between 1 and 8 nm. To describe the adsorption of the pyridine molecule onto the metal surface, we have implemented a coordination-dependent force field to differentiate the various local surface environments. We find that the DIM/QM method predicts geometries and frequencies that are in good agreement with full QM simulations and experiments. For the simulated SERS spectra of pyridine, we find a significant dependence on the adsorption site and the size of the metal nanoparticle. This illustrates the importance of accounting for the local environment around the molecule. The Raman enhancement factors are shown to roughly mirror the magnitude of the nanoparticle's local field about the molecule. Because the simulated nanoparticles are small, the plasmon peaks are quite broad which results in weak local electric fields and thus modest Raman enhancement factors.     

密度泛函理论研究银上吸附对巯基吡啶的SERS化学增强效应

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SERS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v9a的拉曼信号。     

Surface-enhanced raman scattering from poly(4-vinyl pyridine)

Surface-enhanced Raman scattering (SERS) has been observed for poly(4-vinyl pyridine) absorbed onto silver island films. Bands near 1219 and 1613 cm^?1, which are weak in normal Raman spectra of PVP, are strong in SERS spectra, and the band near 1020 cm^?1, which is the strongest band in the normal spectra, is relatively weak in SERS. The strongest bands in the SERS spectra all belong to the same symmetry species as α_ZZ, implying that the pyridine moieties are adsorbed through the nitrogen atoms with a vertical conformation. The ring breathing mode of the pyridine rings is observed near 1020 cm^?1, a frequency characteristic of pyridinium ions or coordinated pyridine, providing further evidence for adsorption through the nitrogen atoms. Silver catalyzed photooxidation, which can lead to the appearance of artifacts in SERS spectra, particularly of polymers, can be reduced by overcoating SERS samples with thin films of polymers such as poly(methyl methacrylate) that have low Raman scattering cross sections.     

Normal raman scattering from pyridine adsorbed on the low-index faces of silver

We find no enhancement of the Raman scattering cross section for pyridine adsorbed at 120 K on the (100), (110) and (111) faces of silver in ultrahigh vacuum. The frequencies we observe are essentially unshifted from those of liquid pyridine, intensity ratios are similar to the liquid, the signal intensity is linear in coverage from submonolayer to multilayer, and the depolarization ratio is low. Since these observations are in marked contrast to those associated with surface-enhanced Raman scattering (SERS), we conclude that our spectra result from normal Raman scattering. Our results support the hypothesis that special adsorption sites are responsible for a substantial fraction of the total enhancement of the Raman cross section for the pyridine - silver system.     

Surface-enhanced raman scattering (SERS) of adsorbed molecules on smooth surfaces of metals and a metal oxide

Surface-enhanced Raman spectra were observed for pyridine adsorbed on Ni, Pd and Pt (vacuum evaporated films) as well as on Ag and Au. The υ_o dependence varied remarkably from metal to metal. SERS of pyridine adsorbed on nickel oxide (cleaved single crystal) was also observed. Langmuir films of stearic acid on Ag showed no feature of SERS.     

The state of metals in the Pt/Al2O3 and (Pt-Cu)/Al2O3 catalysts as indicated by IR spectroscopy with isotope dilution of 12C16O with 13C18O molecules

Adsorption of ¹³C¹⁸O+¹²C¹⁶O mixtures on the Pt(2.9%)/γ-Al₂O₃, (Pt(2.6%)+Cu(2.7%))/γ-Al₂O₃, and (Pt(2.6%)+Cu(5.1%))/γ-Al₂O₃ catalysts was studied by FTIR spectroscopy. On the metallic Pt surface at coverages close to saturation, CO is adsorbed both strongly and weakly to form linear species for which the vibrational frequencies of the isolated ¹³C¹⁸O molecules adsorbed on Pt are ∼1940 and ∼1970 cm⁻¹, respectively. The redistribution of intensities of the high-and low-frequency absorption bands in the spectra of adsorbed ¹³C¹⁸O indicates that these linear forms are present on the adjacent metal sites. The weak adsorption is responsible for the fast isotope exchange between the gaseous CO and CO molecules adsorbed on metal. The Pt-Cu alloys, in which the electronic state of the surface Pt atoms characteristic of monometallic Pt remains unchanged, are formed on the surface of the reduced Pt-Cu bimetallic catalysts. The decrease in the vibrational frequencies of the isolated C=O bonds in the isolated Pt-CO complexes suggests that the CO molecules adsorbed on the Cu atoms affect the electronic properties of Pt. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 5, pp. 831–836, May, 2007.     

Surface-enhanced Raman scattering measurements on silver nanoparticles covered with differently formed platinum films

Gold and silver electromagnetic nanoresonators covered by a thin layer of platinum are often used to study adsorption of various molecules on “model platinum surfaces” with surface-enhanced Raman scattering (SERS) spectroscopy. In this contribution spectra of pyridine adsorbed on films formed from core–shell Ag@Pt and Ag@Ag–Pt nanoparticles and pure Pt or Ag nanoparticles were measured using a confocal Raman microscope. The SERS spectra of pyridine adsorbed on alloy Ag@Ag–Pt nanoparticles could not be obtained as a linear combination of spectra measured on pure Ag and Pt surfaces. In other words, for silver electromagnetic nanoresonators covered by platinum there is no simple correlation between the “quality” of the deposited Pt layer and the relative intensity of SERS bands characteristic for adsorbate interacting with silver. The SERS spectra accumulated from various places of a film formed from Ag@Pt or Ag@Ag–Pt nanoclusters may differ significantly. Using Ag@Pt nanoparticles with practically negligible amount of Ag on the surface (as per the stripping measurement), it is possible to record SERS spectrum in which the contribution characteristic for pyridine adsorbed on the Ag surface is well visible. It means that, even for macroscopic samples of core–shell Ag–Pt nanoparticles, averaging of many spectra measured at various locations of the sample should be carried out to characterize reliably their properties.