烷烃客体分子(CnHm, n≤6, m≤14)在51262和51264水笼中的稳定性与拉曼光谱的密度泛函理论计算

可燃冰矿藏中气体成分非常复杂,通过谱学分析对水合物样品成分进行指认具有重要意义.基于B97-D/6-311++G（2d,2p）的密度泛函理论（DFT）计算,我们系统地探索了构成水合物的两种标准水笼（5¹²6²和5¹²6⁴）包络十八种不同烷烃客体分子的稳定性. 从计算结果可以看出,除了3-甲基戊烷和2,3-二甲基丁烷两个烷烃客体分子,其它16个烷烃客体分子都可以被容纳在5¹²6²笼中;但是与5¹²6²笼不同,十八种烷烃客体分子都可以被容纳在尺寸较大的5¹²6⁴笼中. 同时,我们也模拟了五种直链烷烃和四种环状烷烃在5¹²6²和5¹²6⁴笼中相应的谱学特征,从拉曼谱图上可以看出,随着碳原子数量的增多,直链烷烃客体分子C―H键伸缩振动区的多数拉曼谱带向高波数移动,而环状烷烃客体分子C―H键伸缩振动区的拉曼谱带则向低波数移动. 这些结果为实验上通过拉曼谱测量指认水合物矿藏的成分提供理论参考.     

麻黄碱的密度泛函理论计算及拉曼光谱研究

用密度泛函理论B3LYP/6-311G++(d, p)方法优化了麻黄碱分子结构,计算了理论拉曼光谱,以此为依据,对麻黄碱的常规拉曼光谱进行了详细的指认,用Gaussview5.0软件对其峰位进行了详细的归属。采用了自组装方法,经氨基化处理后的玻片与银溶胶结合,获得了具有二维结构的纳米银基底,研究了沉积在基底表面麻黄碱的表面增强拉曼光谱,结果表明,实验所得拉曼光谱与理论计算拉曼光谱基本一致,该分子与银纳米表面化学吸附,苯环与银基底垂直。该研究为麻黄碱的快速、痕量检测提供了理论依据,也为冰毒类毒品拉曼光谱分析提供了重要参考。     

液态聚乙二醇CH_2剪切振动和扭转振动——拉曼光谱和密度泛函理论计算

提出了一种新方案,以有效洞察液态中共存构象异构体对聚氧乙烯(PEO)实际振动光谱的贡献。通过定义6种-(CH_2CH_2O)-重复单元构象,构建并优化得到4种全同EO构象组合[(TGT)_(10)、(TTT)_(10)、(TTG)_(10)和(GTG)_(10)]和3种其它EO构象组合的构象异构体结构,并在PCM溶剂模型和B3LYP/6-31G(d)理论水平下,对结构进行了优化和振动频率计算。通过振动模式分析,提出描述PEO400各构象异构体的不同CH_2剪切振动和CH_2扭转振动模式的统一标准,确定了4种CH_2CH_2-O-CH_2CH_2链段构象和相关振动模式,以及它们与振动频率大小的关系,并应用于实际拉曼光谱的指认。     

密度泛函理论研究5-单苯基卟啉分子的几何结构和拉曼光谱

利用密度泛函理论(DFT)计算了5-单苯基卟啉(H2MPP)的几何结构和拉曼振动频率. 计算表明, 单个次甲基位置上的苯基取代降低了卟啉骨架大环的对称性. 苯基团取代对次甲基位置附近结构的影响较大, 而对吡咯环结构的影响较小. 计算给出的拉曼振动频率(校正因子为0.971)与实验测量数据吻合较好, 均方根误差(RMS)小于6.7 cm-1. 根据理论计算结果对实测拉曼光谱进行了指认, 计算分析和实验观察同时表明, 单个次甲基位置上的苯基取代导致卟啉大环的一些平面内简正振动, 如ν6、ν20、ν24和ν32等简正振动发生分裂. 分析认为其根本原因为单苯基取代导致的卟啉骨架大环对称性的降低.     

三甲胺表面增强拉曼光谱的密度泛函理论研究

三甲胺(Trimethylamine,TMA)是衡量畜禽水产及其制品中腐败程度重要指标.表面增强拉曼光谱技术在纳米级ⅠB族金属粗糙结构上具有极高检测灵敏度.目前,TMA表面增强拉曼光谱实验研究还未见报道,所以理论得到TMA表面增强拉曼谱图并和实验结果对比具有重要意义.将表面增强拉曼光谱与密度泛函理论(DFT)结合,研究...     

Fe-AlPO4-5 分子筛的共振拉曼光谱

利用周期性密度泛函的方法,将过渡金属杂原子取代的硅基分子筛的共振拉曼计算结果成功推广到磷铝分子筛体系中.根据对Fe-ZSM-5共振拉曼光谱特点的推广和对Fe-AlPO4-5振动光谱的理论计算结果,预测在Fe-AlPO4-5的共振拉曼光谱的1190、1130、1000-1050和600 cm-1位置附近将出现四条显著的谱带.实验的Fe-AlPO4-5的共振拉曼光谱中确实观察到四条与骨架Fe物种相关的谱带分别位于1210、1130、1050和630 cm-1处,与预测结果一致.另外发现含铁磷铝分子筛的共振振动频率要高于相应的含铁硅基分子筛体系的振动频率,这种频率的差异主要是氧在不同分子筛体系中受力的力常数不同引起的.另外磷氧四面体和铝氧四面体之间的电荷吸引作用对振动频率也有较大的影响.     

I2-环己烯复合物的共振拉曼光谱和密度泛函理论计算研究

实验得到I2-环己烯电荷转移复合物的电子吸收光谱和共振拉曼光谱.用密度泛函方法计算了复合物的基态结构、振动频率和电子跃迁能.计算和吸收光谱实验结果表明,I2-烯烃复合物在约300nm处的强吸收带为pz(I17)→π*(C=C)跃迁,即由靠近C=C双键端的碘原子(I17)上的一个pz电子向C=C双键反键轨道跃迁引起的吸收.在约300nm共振拉曼光谱的强度模式表现为I—I伸缩振动模和C=C伸缩振动模的基频、泛频及其组合频,表明在该激发态上I2-环己烯复合物经历了显著的I—I和C=C的价键变化.     

弱氢键作用对硫脲水溶液拉曼光谱影响的密度泛函理论计算

将拉曼光谱和密度泛函理论(DFT)计算结合能够把拉曼谱峰和分子结构及分子间氢键作用之间的变化联系起来, 反映分子周围的结构信息. 本文通过理论计算水分子和硫脲形成复合物的拉曼光谱, 并结合实验报道的拉曼光谱, 探究硫脲基频对分子局域结构的依赖性. 通过轨道分析, 发现水分子的氢键作用可以引起硫脲的前线轨道对易, 这将影响到硫脲的拉曼光谱性质. 最后计算也表明在中性水溶液中由于大的正Gibbs 自由能变, 硫脲不易发生异构转变.     

弱氢键作用对硫脲水溶液拉曼光谱影响的密度泛函理论计算

将拉曼光谱和密度泛函理论(DFT)计算结合能够把拉曼谱峰和分子结构及分子间氢键作用之间的变化联系起来,反映分子周围的结构信息.本文通过理论计算水分子和硫脲形成复合物的拉曼光谱,并结合实验报道的拉曼光谱,探究硫脲基频对分子局域结构的依赖性.通过轨道分析,发现水分子的氢键作用可以引起硫脲的前线轨道对易,这将影响到硫脲的拉曼光谱性质.最后计算也表明在中性水溶液中由于大的正Gibbs自由能变,硫脲不易发生异构转变.     

咪唑菌酮的密度泛函理论计算模拟及表面增强拉曼光谱快速测定EI北大核心CSCD

Density functional theory （DFT） was used to identify and assign the Raman spectra of fenamidone, and a simple and rapid surface-enhanced Raman spectroscopy （SERS）detection method for fenamidone was established. Gold nanoparticles （AuNPs）were synthesized via an improved reduction method of chloroauric acid with the trisodium citrate. DFT was used to optimize the geometric configuration of fenamidone, so as to identify and assign the vibration modes of SERS spectra. The simulated spectra were compared to that of the standard solution as well as the tobacco matrix spiked solution.The SERS detection limit of fenamidone was 0.01 mg/kg in the standard solution and 0.02 mg/kg in tobacco matrix spiked solution. In the range of 0.1-5 mg/L, there was a good linear response between SERS intensity and the logarithm of fenamidone concentrations, with the correlation coefficient （R2） of 0.9658. The relative standard deviations （RSDs）were less than 2.6%. This method is suitable for the determination of fenamidone residues in tobacco samples. © 2023 the authors.     

Vibrational Spectra and Density Functional Theory Calculations of Metallo-tetra-(tert-butyl)-tetra-azaporphyrines

The infrared absorption and 514.5 nm excited Raman spectra were measured for the metallo-tetra-(tert-butyl)-tetraazaporphyrin (MT(tBu)TAP, M=Cu, Co, Ni, Zn). The ground-state structures and vibrational spectra of MT(tBu)TAPs have been calculated at the B3LYP level of theory. The observed Raman and IR bands have been assigned based on the calculation results and by comparing with the normal metalloporphyrins. The relationship between the Raman/IR frequencies and the structures of TAP ring was investigated. The results show that the frequencies of C_βC_β′ stretch (A_g), asymmetric C_αN_m stretch (A_g), and symmetric C_αN_m stretch (B_g) modes increase linearly with the decrease of the core-sizes of TAP ring.Among the three modes, the later two are more sensitive to the core-size change.     

Vibrational Spectra and Density Functional Theory Calculations of Metallotriphenylcorroles

The infrared absorption and Raman scattering spectra were measured for the metallotriph-enylcorroles (MTPCs, M=Cu, Co, Ni, Mn). The ground-state structures and vibrational spectra of MTPCs have been calculated with the density functional theory. The observedRaman and IR bands have been assigned based on the calculation results. Due to the symmetry lowering, the vibrational spectra of MTPCs are much more complex than metal-loporphyrins, and several skeletal modes are found strongly coupled to the phenyl vibrations.The relationship between the Raman/IR frequencies and the structures of TPC ring is in-vestigated. It is found that the vibrations involving the C^I_αC^I_α stretch and C_αC_mstretch are sensitive to the size of corrole core. In particular, the frequency of υ₅, which is assigned to C^I_αC^I_α stretch in coupling with the C_αC_m symmetric stretch, increases linearly with the decrease of the corrole core-sizes and may be used as a mark band to evaluate the structural change of the metallocorroles.     

Density Functional Theory Study for Adsorption of Oxygen and Water Molecules on 6H-SiC(0001) Surface

6H-SiC is an important semiconductor material. The 6H-SiC wafer is always exposed to a high-humidity environment and the effect from the absorbed water molecule and some relative adsorbates is not negligible. Here, the oxygen and water molecules absorbed on the 6H-SiC(0001) surface and the dissociation process were studied with density functional theory. On the 6H-SiC(0001) surface, absorbed O₂ is spontaneously dissociated into O^*, which is absorbed on a hollow site, and further transforms the 6H-SiC(0001) surface into SiO₂. The absorbed H₂O is spontaneously broken into OH^*and H^*, which are both absorbed on the top of the Si atom, and OH^* is further reversibly transformed into O^* and H^*. The H^* could saturate the dangling Si bond and change the absorption type of O^*, which could stabilize the 6H-SiC(0001) surface and prevent it from transforming into SiO₂.     

6-硫代黄嘌呤互变异构体的密度泛函理论计算

在密度泛函B3LYP/6-311G**水平下,对14种气相和水相中可能存在的6-硫代黄嘌呤异构体进行了几何构型的全自由度优化,并计算出它们的总能量、焓、熵、吉布斯自由能。Onsager反应场溶剂模型用于水相的计算.计算结果表明,6-硫代黄嘌呤在气相中和水相中主要以硫酮的形式存在.在气相和水相中,硫酮-N7(H)均比硫酮-N9(H)更稳定.计算结果同已有实验结果一致.6-硫代黄嘌呤异构化的熵效应小,对互变异构平衡几乎没有显著的影响,而焓变对互变异构产生了主要的影响.较详细地讨论了水溶剂化作用对异构体的能量、几何结构、电荷分布和偶极矩的影响.     

双氰胺在金团簇上吸附的密度泛函理论和表面增强拉曼光谱研究

双氰胺是氰胺的二聚体,具有亚氨式和氨式两种互变异构体.将表面增强拉曼光谱(SERS)与密度泛函理论(DFT)结合,研究了互变异构的双氰胺分子在金表面的吸附行为.通过理论计算获得了亚氨式和氨式双氰胺分子的能量、分子轨道和光谱信息,以及双氰胺分子吸附在金簇表面的SERS响应.计算结果表明两种异构化的双氰胺分子都与Au₃簇形成较稳定的复合物,并且双氰胺分子中N₂原子优先吸附在金簇表面.拉曼实验结果与计算结果较为吻合,进一步说明具有互变异构的双氰胺分子在金基底中共存,并通过N₂原子垂直吸附到金表面,符合SERS电磁场增强机制.