The interfacial structure of water/protonated α-Al2O3 (11 ?20) as a function of pH

Sum frequency vibrational spectroscopy (SFVS) was used to study the structure of the protonated α-Al(2)O(3) (11 ?20), and water/α-Al(2)O(3) (11 ?20) interfaces as a function of pH. By combining SFVS spectra with an oxygen-terminated model suggested by x-ray reflectivity, we are able to understand several details of the protonated α-Al(2)O(3) (11 ?20) interface structure. For example, the spectral changes observed for the water/α-Al(2)O(3) (11 ?20) interface with varying pH could be accounted for by the protonation/deprotonation of particular surface hydroxyls. Our spectra also indicate that the point of zero charge for this interface is at pH ~ 6.7.     

Impact of intermolecular vibrational coupling effects on the sum-frequency generation spectra of the water/air interface

ABSTRACT

We have examined the impact of intermolecular vibrational coupling effects of the O-H stretch modes, as obtained by the surface-specific velocity-velocity correlation function approach, on the simulated sum-frequency generation spectra of the water/air interface. Our study shows that the inclusion of intermolecular coupling effects within the first three water layers, i.e. from the water/air interface up to a distance of 6?Å towards the bulk, is essential to reproduce the experimental SFG spectra. In particular, we find that these intermolecular vibrational contributions to the SFG spectra of the water/air interface are dominated by the coupling between the SFG active interfacial and SFG inactive bulk water molecules. Moreover, we find that most of the intermolecular vibrational contributions to the spectra originate from the coupling between double-donor water molecules only, whereas the remaining contributions originate mainly from the coupling between single-donor and double-donor water molecules.     

空气/水界面水分子的取向和运动

对四种不同的实验构型下空气／水界面自由O-H键在3700cm~(-1)的和频振动光谱的分析表明,水分子在空气／水界面的取向运动只可能是在平衡位置附近有限角度之内的受限转动。界面水分子的自由O-H键取向距界面法线约33°,而取向分布或运动的宽度不超过15°。这一图像显著地不同于Wei等人(Phys. Rev. Lett.86,4799(2001))只通过单一的SFG实验构型所得出结论,即：空气／水界面的水分子在超快的振动弛豫时间内在很大的角度范围内运动。     

Anharmonic couplings underlying the ultrafast vibrational dynamics of hydrogen bonds in liquids

The multilevel structure and vibrational couplings of O-H stretching transitions in intermolecular hydrogen bonds of acetic acid dimers are determined by femtosecond two-dimensional photon-echo spectroscopy in the infrared. Combining experiment and theoretical calculations, we separate Fermi resonances with combination tones of fingerprint modes from anharmonic couplings to underdamped low-frequency modes of the dimer. A multilevel density matrix approach based on density functional theory calculations reproduces the experimental results and reveals coupling strengths of both mechanisms on the order of 40-150 cm(-1).     

Ultrafast vibrational energy transfer between surface and bulk water at the air-water interface

We report a femtosecond time-resolved study of water at the neat water-air interface. The O-H stretch vibrational lifetime of hydrogen-bonded interfacial water is measured using surface-specific 4th-order nonlinear optical spectroscopy with femtosecond infrared pulses. The vibrational lifetime in the frequency range of 3200 to 3500 cm(-1) is found to closely resemble that of bulk water, indicating ultrafast exchange of vibrational energy between surface water molecules and those in the bulk.     

Sum-frequency vibrational spectroscopic studies of Langmuir monolayers

Surface-sensitive sum-frequency vibrational spectroscopy (SFVS) has grown into a most viable analytical tool to investigate Langmuir monolayer systems. It has been successful in deducing information on many key properties of Langmuir films not obtainable by other techniques. This review gives a survey on the current status of SFVS studies of Langmuir monolayers with emphasis on the structures of both surfactant monolayers and interfacial water under various circumstances.     

Molecular structure of polystyrene at Air/Polymer and Solid/Polymer interfaces

IR-visible sum-frequency generation (SFG) spectroscopy has been used in a total internal reflection geometry to study the molecular structure of polystyrene (PS) at PS/sapphire and PS/air interfaces, simultaneously. The symmetric vibrational modes of the phenyl rings dominate the SFG spectra at the PS/air interface as compared to the antisymmetric vibrational modes at the PS/sapphire interface. This indicates approximately parallel orientation of the phenyl rings at the PS/air interface while nearly perpendicular orientation at the PS/sapphire interface, with respect to the surface normal.     

有机磷农药甲基对硫磷的太赫兹(THz)光谱研究

运用太赫兹时域光谱技术(THz-TDS)与理论模拟相结合的方法研究了有机磷农药甲基对硫磷在THz波段的光谱特性。在室温氮气环境中得到了样品在0.2～2.0 THz波段的吸收谱和折射率谱。表明其特征吸收峰分别位于0.65,1.33,1.81和1.91 THz处,其平均折射率为1.39。同时运用密度泛函理论(DFT)计算了甲基对硫磷分子的结构及其在太赫兹波段的振动频率,计算结果与实验数据吻合较好。研究结果表明,实验光谱的特征吸收峰是由分子的集体振动及扭转形成,不同的吸收峰位对应分子不同的振转模式。     

异丙醇的O-H伸缩振动泛频光谱和分子构像

使用高灵敏的光腔衰范光谱（Ｃａｕｉｔｙ Ｒｉｎｇ Ｄｏｗｎ Ｓｐｅｃｔｒｏｓｃｏｐｙ）技术测出了异丙醇的Ｏ－Ｈ伸缩ｖ＝４、５振动泛频光谱,每个技动能级都有三个吸收峰,被归属为分子构像的Ｏ－Ｈ伸缩泛叔汲收,给出了光腔衰范光谱的振动泛频吸收的振动谱强度公式,并求得分子不同构在不同振动能级的Ｏ－Ｈ伸缩局域模振子的机械频率（Ｘ１）、非谐性（Ｘ２）以及解离能（Ｄ）,用浓度泛函（ＤＦＴ）Ｂ３ＬＹＰ／６－３１＋     

对巯基苯胺分子构象和拉曼光谱的密度泛函理论研究

本文采用密度泛函方法B3LYP/6-311+G**计算了对巯基苯胺分子(PATP)的平衡结构和振动拉曼光谱。结果表明该分子有两个稳定构象,反式构象能更低。利用振动模分析所得的势能分布我们对该分子振动基频进行了归属,并计算了低能构象的标度振动频率,其结果与实验值相吻合。     

金属/乙腈界面微量水的增强拉曼光谱

本文概述了我们最近利用表面增强拉曼散射技术研究金属 /乙腈界面区痕 /微量水分子的界面行为所取得的进展。研究表明银电极双电层中存在多种吸附模式下的水分子结构。处于非水环境下的水分子的νO H与水系相比存在明显的差别。水分子间的氢键被不同程度地破坏导致几种模式下的水分子νO H均要高于水体系。铂电极表面的研究表明水分子的介入很大程度上限制了铂表面乙腈分子的解离吸附反应。     

Raman and DFT study of hydrogen‐bonded 2‐ and 3‐chloropyridine with methanol

Precise polarized Raman measurements of 2‐chloropyridine (2Clpy) in the region 560–1060 cm⁻¹ and 3‐chloropyridine (3Clpy) in the region 680–1080 cm⁻¹ at different concentrations in mole fraction of methanol were made to calculate the isotropic part of the Raman spectra, which has contributions only from vibrational dephasing. A detailed analysis of the Raman spectra was carried out to see the variation of peak position and linewidth. The dephasing is mode specific. The trigonal bending mode of 3Clpy has two components when it is mixed with methanol. The relative intensities of these two bands are used to calculate the equilibrium constants. The ring‐breathing mode of 3Clpy, on the other hand, remains single in the mixture. The appearance of a new band corresponding to the trigonal bending mode, as well as the nonappearance of that of the ring‐breathing mode, is also shown by the density functional theory (DFT) study of gas phase and methanol‐solvated complexes. The vibrational dephasing time for the hydrogen‐bonded ring‐breathing mode is calculated from the linear Raman linewidth and peak position data. For other modes, it was not possible to calculate the dephasing time because of the nonavailability of a suitable theoretical model. Contrary to 3Clpy, in 2Clpy the ring‐breathing mode becomes a doublet but the trigonal bending mode remains single. It is seen that the hydrogen‐bonding capacity of chloropyridines is highly influenced by the position of the Cl atom. Single and double components of these modes are also explained by DFT calculations. We obtained excellent match of the experimental and theoretical spectra with the B3LYP/6‐31 + G (d,p) method. Copyright © 2008 John Wiley & Sons, Ltd.     

Investigation of hydrogen bonding in neat dimethyl sulfoxide and binary mixture (dimethyl sulfoxide + water) by concentration-dependent Raman study and ab initio calculation

In this study,our vibrational spectroscopic analysis is made on hydrogen-bonding between dimethyl sulfoxide and water comprises both experimental Raman spectra and ab initio calculations on structures of various dimethyl sulfoxide/water clusters with increasing water content.The Raman peak position of the v(S=O) stretching mode of dimethyl sulfoxide serves as a probe for monitoring the degree of hydrogen-bonding between dimethyl sulfoxide and water.In addition,the two vibrational modes,namely,the CH 3 symmetric stretching mode and the CH 3 asymmetric stretching mode have been analysed under different concentrations.We relate the computational results to the experimental vibrational wavenumber trends that are observed in our concentration-dependent Raman study.The combination of experimental Raman data with ab initio calculation leads to a better knowledge of the nature of the hydrogen bonding and the structures of the hydrogen-bonded complexes studied.     

β-D-吡喃半乳糖的太赫兹光谱研究

为深入了解β-D-吡喃半乳糖在太赫兹波段的光谱特性, 利用太赫兹时域光谱技术测量了室温下β-D-吡喃半乳糖晶体在0.3～3.0 THz范围内的吸收谱及折射率谱, 同时利用傅里叶变换红外光谱技术获得了半乳糖在1.5～19.5 THz之间的吸收谱。实验研究的同时, 运用密度泛函理论和6-311+G**基组计算了气态孤立β-D-吡喃半乳糖分子的结构及其在太赫兹波段的振动频率, 并据此对实验光谱吸收峰进行了指认。研究结果表明, 除了因为分子间效应而导致的少许偏移外, 理论计算结果与实验数据吻合得很好; 实验光谱在6 THz以上频段的共振吸收峰来源于明确的分子内振动模式, 而6 THz以下低频段的共振吸收峰则主要来源于分子间氢键或晶体的声子模式。实验和理论研究的对比表明物质的远红外吸收特征对于分子的结构和空间排列非常敏感。     

Surface enhanced Raman scattering in organic thin films covered with silver, indium and magnesium

In situ resonant Raman spectroscopy was applied for the investigation of the interface formation between silver, indium and magnesium with polycrystalline organic semiconductor layers of 3,4,9,10-perylene tetra-carboxylic dianhydride (PTCDA). The spectral region of internal as well as external vibrational modes was recorded in order to achieve information related to the chemistry and the structure of the interface as well as to morphology of the metal layer. The experiments benefit from a strong enhancement of the internal mode scattering intensities which is induced by the rough morphology of deposited metals leading to surface enhanced Raman scattering (SERS). The external modes, on the other hand, are attenuated at different rates indicating that the diffusion of the metal atoms into the crystalline layers is highest for indium and lowest for magnesium.     

Musical acoustics of orchestral water crotales

An experimental investigation of orchestral crotale vibrational modes in water is presented, along with a qualitative virtual mass model describing the observed effects. Changes in frequency, overtone ratio, and mode splitting as a function of water depth are reported for a C(6) crotale using electronic speckle-pattern interferometry. These data are related to perceived changes in pitch and timbre, along with the creation of audible beats at particular water depths. It is also shown that the suspension method used by musicians when dipping crotales into water leads to the creation of additional acoustically significant modes that are not excited when the crotales are mounted in the standard manner.     

An FTIR study of the bonding of methoxy on Ni(100): effects of coadsorbed sulfur, carbon monoxide and hydrogen

The vibrational spectra of CH₃O_(a), CD₃O_(a), CDH₂O_(a) and CD₂HO_(a) on Ni(100) are analyzed and interpreted in terms of resonances between fundamental modes and either combinations or overtones. Analysis of the symmetry of the modes observed suggests that methoxy binds normal to the surface with C_s symmetry, at least at low coverages. Two distinct vibrational bands emerge in the vibrational spectrum of methoxy in the v(CO) region as the coverage increases which are attributed to bonding in four-fold hollow sites and bridging sites. These bands exhibit blue shifts of about 25 cm⁻¹ with increasing coverage up to the saturation coverage. The vibrational bands in the v(CH) region appear concomitantly at all coverages and shift down 12 cm⁻¹ as the coverage is increased. These shifts are attributed to changes in the metal-oxygen bond which are reflected in changes in the strength of the C---O and C---H bonds. Affects on the bonding also appear to occur with the coadsorption of hydrogen or CO with methoxy. Coadsorption of 0.36 ML hydrogen with 0.04 ML methoxy induces blue shifts of 15 and 7 cm⁻¹ for the v(CO) bands at 949 and 984 cm⁻¹, respectively. Adsorbing 0.43 ML of CO with 0.04 ML methoxy (and 0.04 ML hydrogen) causes a red shift of 20 and 12 cm⁻¹ for these bands. A drastic drop in mode intensities for methoxy when CO is coadsorbed suggests that the methoxy tilts away from the surface normal. Pre-adsorbing sulfur on the Ni(100) surface reduces the amount of methoxy formed from methanol, but the v(CO) methoxy bands are unshifted in frequencies relative to their position for the same methoxy coverage on the clean surface.     

A FT-IR absorption analysis of vibrational properties of water encaged in NaA zeolites: evidence of a "structure maker" role of zeolitic surface

We performed, in the O-H stretching region, Fourier-transform Infrared (FT-IR) Absorption measurements for investigating the vibrational dynamics on water confined in NaA zeolite, vs. temperature and for different hydration percentages. The spectral substructure of the O-H stretching band is explained postulating the existence of three major components centred at approximately 3290 cm(-1) (omega(1)), approximately 3470 cm(-1) (omega(2)), approximately 3590 cm(-1) (omega(3)), with different dynamical properties traced over the full T-range investigated.     

不同晶粒尺寸SnO2纳米粒子的拉曼光谱研究

对晶粒尺寸在4—80nm范围的纯SnO₂纳米颗粒进行了拉曼散射研究.除了SnO₂本征拉曼振动峰外，还有几个新的拉曼振动峰和波长在700nm左右的一个发光很强而且峰宽很大的荧光峰被观察到.结果所示，当纳米颗粒尺寸减小时，纳米SnO₂颗粒的体相 特征拉曼峰变弱，而由缺陷，表面和颗粒尺寸引起的相关效应呈强势.晶粒尺寸在20nm左右是引起体相拉曼光谱变化的临界尺寸.晶粒尺寸在20nm以下，其体相拉曼峰的发生宽化和峰位移动，以及分别出现在位于571cm^-1 的表面振动峰，位于351cm-1 处的界面峰和与表面吸附水分子及氢氧基团的N系列拉曼峰是纳米SnO颗粒的主要特征.这些结果反映了纳米颗粒的微结构变化与颗粒尺寸和表面效应以及它们之间相互作用的信息. 关键词： ２')" href="#">纳米SnO_２ 拉曼光谱 荧光光谱 水分子的吸附     

持久性有机物硫丹的太赫兹光谱研究

以最新被斯德哥尔摩公约列入持久性有机污染物的硫丹为研究对象,采用太赫兹时域光谱技术获得了α硫丹在0.2～2THz频率范围内的吸收系数谱和折射率谱,结果显示在此频率范围内存在有一系列特征吸收峰,并且通过实验和理论计算对比发现在1.70和1.88THz处的实验吸收峰与1.68和1.91THz处的理论吸收峰有很好的吻合;经分析认为,这吻合峰是由于分子内集体振动引起的,实验中的其他峰值可能归因子分子间弱相互作用力和混合振动。研究结果证明了THz-TDS技术进行持久性有机物检测的可行性,为THz-TDS系统在持久性有机物识别和残留物检测方面的应用提供了依据。