和频与差频振动光谱实验构型的分析模拟

实验构型分析是定量分析和频振动光谱的基础.变换实验构型,不仅要考虑某一振动模式信号强度的大小,还要考虑不同构型下的信号检测效率.现有的和频振动光谱实验构型分析主要考虑前者.本文探讨实验构型分析中所涉及的信号检测效率问题,模拟在共向式和频(差频)及对射式和频(差频)振动光谱实验中选取何种实验构型对采集信号光更加合理有效.利用相干光学过程能量守恒和动量守恒原理,分析了入射角及入射光频率等因素对信号出射角的影响,并模拟了信号出射角与入射角及入射光频率的关系,得到了可选的入射角组合最多、出射角随入射光频率变化最小的实验构型.结果表明,和频振动光谱采取共向式实验构型,差频振动光谱采取对射式实验构型,有利于信号采集,进而有利于用实验构型分析方法对和频(差频)振动光谱进行定量研究.     

和频振动光谱研究多晶金电极/溶液界面乙腈分子取向的flip-flop行为

用和频振动光谱研究乙腈/金电极界面,观测到乙腈的甲基振动峰强度随施加的电极电势而变化.当电极电势越过零电荷电势（pzc）时,甲基振动峰符号发生反转,这意味着基团取向发生反转（flip-flop）.由此推断出乙腈分子在金电极界面的吸附构型.即在零电荷电势下,电极界面吸附的乙腈分子构型为甲基靠近电极表面而腈基远离电极表面;而高于零电荷电势则电极界面吸附的乙腈分子构型发生反转,变为腈基靠近电极表面而甲基远离电极表面的构型.     

和频光谱研究油酸包覆的Fe3 O4 纳米颗粒

采用红外-可见和频振动光谱研究了表面包覆油酸分子的Fe3O4纳米颗粒, 得到了2种实验构型(构型1: 可见光入射角63°, 红外光入射角55°; 构型2: 可见光入射角45°, 红外光入射角55°)和3种偏振组合(ssp, ppp, sps)下的和频振动光谱, 比较了2种实验构型下和频光谱的特征, 通过偏振分析方法对各个光谱峰进行了归属.     

利用和频振动光谱研究空气/短链脂肪酸界面的分子取向

利用和频振动光谱(SFG-VS)方法检测了5种短链脂肪酸分子(乙酸、丙酸、正丁酸、正戊酸及正己酸)在空气/纯液体界面的结构,得到了3种偏振组合(ssp,PPP,sps)下的和频振动光谱.通过偏振选择定则对各个谱峰进行了指认和分析,同时计算出空气/纯脂肪酸液体界面上脂肪酸分子的甲基取向角.对比发现,从丙酸到己酸,分子甲基基团的界面取向角随碳链的增长略有增大.并对其机理进行了分析.     

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 $切的$ mathrm{alpha} $-石英晶体作为基底,担载少量催化剂粉末样品. 该方法不仅可以通过石英晶体非共振电场的干涉放大界面颗粒上吸附分子的和频振动信号,并获得相位信息,还可以用于宽带红外和频振动光谱进行归一化. 通过分离不同偏振的和频振动信号,能够分离并同时收集手性和非手性的和频振动信号. 使用手性的和频振动信号来归一化非手性的和频振动强度,从而避免因担载物质到石英晶体上或由于不同时刻光的不稳定性引起的界面变化或者光重合差异. 本文通过测量担载有MoC纳米粒子的石英基底上CH$ _3 $OD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.     

CIC（O）NCS分子筛振动光谱的理论研究

采用密度泛函理论DFT（B3LYP）方法,以6－31G为基组对CIC（O）NCS的反式和顺式两种构型的几何结构、振动谐性力场和红外光谱进行了研究 。B3LYP／6－31G的理论力场由适用于B3LYP／6－31G计算水平和大多数有机分子的一套固定标度因子进行标度,根据标度后的理论力场进行简正坐标分析得到的势能分布（PED）和红外光谱强度值对CIC（O）NCS分子物顺式和反式两种构型的振动基频进行了理论归属。     

碱性体系中金电极表面硫氰根离子的宽带和频光谱研究

本文使用宽带和频光谱研究不同电位下碱性溶液中多晶金电极表面硫氰根离子（SCN^-）的吸附行为. 在-1.1 V ~ 0.2 V（vs. SCE）,C-N伸缩振动的Stark斜率的变化表明,随着电位正移,SCN^-在金电极表面从N端吸附变为S端吸附. 在较正电位下,C-N伸缩振动具有Fano线型. 这是因为金的费米能级随电位的正移而降低,和频过程中金的电子跃迁方式从带内跃迁（sp→sp）变为带间跃迁（d→sp）,造成金基底与表面吸附SCN^-和频信号的相对相位改变. 实验表明,通过研究和频光谱线型随电位的变化可以获取电极表面电子能级相对位置的信息.     

在空气下制备掺二价稀土的硼酸盐及二价稀土离子(RE2+=Sm,Eu,Tm,Yb)的光谱特征

本文讨论了Sm2 、Eu2 、Tm2 、Yb2 等二价稀土离子的光谱特征 ,特别是在一些含四面体硼酸根的硼酸盐如SrB4 O7、SrB6 O10 和BaB8O13中它们的光谱性质。当以三价稀土离子取代化合物中的二价碱土离子时 ,利用不等价取代而产生的缺陷所带的电荷 ,可在高温的空气下使上述的稀土离子还原成二价 ,不需加入化学还原剂 ,从而提出了一个简便、安全的制备含二价稀土离子发光材料的方法     

H^＋3O和H^＋3（H2O）n（n=1,2,3）阳离子振动力场和光谱频…

本文利用多原子分子振动力场的模型势函法对Ｈ＾＋３Ｏ和Ｈ＾＋３Ｏ（Ｈ２Ｏ）ｎ（ｎ＝１～３）阳离子的振动力场作了理论计算，并对其光谱频率进行了预测。Ｈ＾３Ｏ和Ｈ＾＋９Ｏ４的振动频率的结果优于从头算梯度法的结果。本文首次给出了Ｈ＾５＋５Ｏ２、Ｈ＾＋７Ｏ３伸缩振动频率的理论预测值。     

Methanol Perturbing Modeling Cell Membranes Investigated using Linear and Nonlinear Vibrational Spectroscopy (cited: 3)

Cell membranes play a crucial role in many biological functions of cells. A small change in the composition of cell membranes can strongly influence the functions of membrane-associated proteins, such as ion and water channels, and thus mediate the chemical andphysical balance in cells. Such composition change could originate from the introduction of short-chain alcohols, or other anesthetics into membranes. In this work, we have applied sum frequency generation vibrational spectroscopy (SFG-VS), supplemented by attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR), to investigate interaction between methanol and 1,2-dimyristoyl-d54-sn-glycero-3-phosphocholine (d54-DMPC) lipid bilayers. Lipid's hydrocarbon interior is deuterated while its head group is hydrogenated. At the same time, CH₃ symmetric stretch from methanol and lipid head amine group has different frequency, thus we can distinguish the behaviors of methanol, lipid head amine group, and lipid hydrocarbon interior. Based on the spectral feature of the bending mode of the water molecules replaced by methanol, we determined that the methanol molecules are intercalated into the region between amine and phosphate groups at the lipid hydrophilic head. The dipole of CH₃ groups of methanol and lipid head, and the water O-H all adopt the same orientation directions. The introduction of methanol into the lipid hydrophilic head group can strongly perturb the entire length of the alkyl chains, resulting that the signals of CD₃ and CD₃ groups from both leaflets can not cancel each other.     

Interaction between Potassium Phosphate Bu er Solution and Modeling Cell Membrane Investigated by Sum Frequency Generation Vibrational Spectroscopy (cited: 1)

Potassium phosphate buffer solution has been widely used in the biological experiments, which represents an important process of the interaction between ions and biomolecules, yet the in fluences of potassium phosphate on biomolecules such as the cell membrane are still poorly understood at the molecular level. In this work, we have applied sum frequency generation vibrational spectroscopy and carried out a detailed study on the interaction between potassium phosphate buffer solution (PBS) and negative 1,2-dimyristoyl-d₅₄-sn-glycero-3-[phospho-rac-(1-glycerol)] (d₅₄-DMPG) lipid bilayer in real time. The PBS-induced dynamic change in the molecular structure of d₅₄-DMPG lipid bilayer was monitored using the spectral features of CD₂, CD₃, lipid head phosphate, and carbonyl groups for the first time. It is found that K⁺ can bind to the cell membrane and cause the signal change of CD₂, CD₃, lipid head phosphate, and carbonyl groups quickly. Potassium PBS interacts with lipid bilayers most likely by formation of toroidal pores inside the bilayer matrix. This result can provide a molecular basis for the interpretation of the effect of PBS on the ion-assisted transport of protein across the membrane.     

和频振动光谱(SFG-VS)研究超铺展三甲基硅烷表面活性剂在空气/水界面的振动光谱和吸附

The C-H stretch vibrational spectra of the trisiloxane superspreading surfactant Silwet L-77((CH3)3Si-O-Si(CH3)(C3H6)(OCH2CH2)7-8OCH3)-O-Si(CH3)3) at the air/water interface are measured with the surface Sum Frequency Generation Vibrational Spectroscopy (SFG-VS). The spectra are dominated with the features from the –Si-CH3 groups around 2905 cm-1 (symmetric stretch or SS mode) and 2957 cm-1 (mostly the asymmetric stretch or AS mode), and with the weak but apparent contribution from the -O-CH2- groups around 2880 cm-1 (symmetric stretch or SS mode). Comparison of the polarization dependent SFG spectra below and above the critical aggregate or micelle concentration (CAC) indicates that the molecular orientation of the C¡H related molecular groups remained unchanged at different surface densities of the Silwet L-77 surfactant. The SFG-VS adsorption isotherm suggested that there was no sign of Silwet L-77 bilayer structure formation at the air/water interface. The Gibbs adsorption free energy of the Silwet surfactant to the air/water interface is -42.2±0.8kJ/mol, indicating the unusually strong adsorption ability of the Silwet L-77 superspreading surfactant     

A Highly Sensitive Femtosecond Time-Resolved Sum Frequency Generation Vibrational Spectroscopy System with Simultaneous Measurement of Multiple Polarization Combinations

Characterization of real-time and ultrafast motions of the complex molecules at surface and interface is critical to understand how interfacial molecules function. It requires to develop surface-sensitive, fast-identification, and time-resolved techniques. In this study, we employ several key technical procedures and successfully develop a highly sensitive femtosecond time-resolved sum frequency generation vibrational spectroscopy (SFG-VS) system. This system is able to measure the spectra with two polarization combinations (ssp and ppp, or psp and ssp) simultaneously. It takes less than several seconds to collect one spectrum. To the best of our knowledge, it is the fastest speed of collecting SFG spectra reported by now. Using the time-resolved measurement, ultrafast vibrational dynamics of the N-H mode of α-helical peptide at water interface is determined. It is found that the membrane environment does not affect the N-H vibrational relaxation dynamics. It is expected that the time-resolved SFG system will play a vital role in the deep understanding of the dynamics and interaction of the complex molecules at surface and interface. Our method may also provide an important technical proposal for the people who plan to develop time-resolved SFG systems with simultaneous measurement of multiple polarization combinations.     

Absolute Orientation of Molecules with Competing Hydrophilic Head Groups at the Air/Water Interface Probed with Sum Frequency Generation Vibrational Spectroscopy

The constructive or destructive spectral interference between the molecular groups oriented up and down at the interface in the sum-frequency generation （SFG） spectra provides a direct measurement of the absolute orientation of these molecular groups. This simple approach can be employed to interrogate absolute molecular orientations other than using the complex absolute phase measurement in the SFG studies. We used the -CN group in the p-cyanophenol （PCP） molecule as the internal phase standard, and we measured the phases of the SFG fields of the -CN groups in the 3,5-dimethyl-4-hydroxy-benzonitrile （35DMHBN） and 2,6-dimethyl-4-hydroxy-benzonitrile （26DMHBN） at the air/water interface by measuring the SFG spectra of the aqueous surfaces of the mixtures of the PCP, 35DMHBN, and 26DMHBN solutions. The results showed that the 35DMHBN had its -CN group pointing into the aqueous phase; while the 26DMHBN, similar to the PCP, had its -CN group pointing away from the aqueous phase. The tilt angles of the -CN group for both the 35DMHBN and 26DMHBN molecules at the air/water interface were around 25°-45° from the interface normal. These results provided insights on the understanding of the detailed balance of the competing factors, such as solvation of the polar head groups, hydrogen bonding and hydrophobic effects, etc., on influencing the absolute molecular orientation at the air/water interface.     

Sum Frequency Generation Vibrational Spectra of Perovskite Nanocrystals at the Single-Nanocrystal and Ensemble Levels

Determination of molecular structures of organic-inorganic hybrid perovskite (OIHP) nanocrystals at the single-nanocrystal and ensemble levels is essential to understanding the mechanisms responsible for their size-dependent optoelectronic properties and the nanocrystal assembling process, but its detection is still a bit challenging. In this study, we demonstrate that femtosecond sum frequency generation (SFG) vibrational spectroscopy can provide a highly sensitive tool for probing the molecular structures of nanocrystals with a size comparable to the Bohr diameter (~10 nm) at the single-nanocrystal level. The SFG signals are monitored using the spectral features of the phenyl group in (R-MBA)PbBr₃ and (R-MBA)₂PbI₄ nanocrystals (MBA: methyl-benzyl-ammonium). It is found that the SFG spectra exhibit a strong resonant peak at 3067±3 cm^-1 (ν₂ mode) and a weak shoulder peak at 3045±4 cm^-1 (ν_7a mode) at the ensemble level, whereas a peak of the ν₂ mode and a peak at 3025±3 cm^-1 (ν_20b mode) at the single-nanocrystal level. The nanocrystals at the single-nanocrystal level tend to lie down on the surface, but stand up as the ensemble number and the averaged sizes increase. This finding may provide valuable information on the structural origins for size-dependent photo-physical properties and photoluminescence blinking dynamics in nanocrystals.     

Methanol Adsorption on TiO2 Film Studied by Sum Frequency Generation Vibrational Spectroscopy (cited:2)

A broadband infrared surface sum frequency generation vibrational spectroscopy (SFG-VS) and an in situ UV excitation setup devoted to studying surface photocatalysis have been constructed. With a home-made compact high vacuum cell, organic contaminants on TiO₂ thin lm surface prepared by RF magnetron sputtering were in situ removed under 266 nm irradiation in 10 kPa O₂ atmosphere. We obtained the methanol spectrum in the CH₃ stretching vibration region on TiO₂ surface with changing the methanol pressure at room temperature. Features of both molecular and dissociative methanol, methoxy, adsorbed on this surface were resolved. The CH₃ symmetric stretching vibration frequency and Fermi resonance of molecular methanol is red-shifted by about 6?8 cm^-1 from low to high coverage. Moreover, the recombination of dissociative methanol and H on surfaces in vacuum was also observed. Our results suggest two equilibria exist: between molecular methanol in the gas phase and that on surfaces, and between molecular methanol and dissociative methanol on surfaces.