金溶胶中邻羟基苯甲酸吸附行为的密度泛函理论与实验研究

研究了邻羟基苯甲酸(OHBA)的常规拉曼散射(NRS)光谱以及其吸附在Au纳米颗粒上的表面增强拉曼散射(SERS)光谱。以氯金酸为原料,柠檬酸三钠为还原剂,用化学还原法制备了球形的金纳米粒子溶胶,采用激光显微拉曼光谱仪(激发波长为785 nm),测定OHBA分子的NRS光谱及其吸附在Au纳米颗粒上的SERS光谱。同时,应用密度泛函理论(DFT),在B3LYP/6-31+G**(C,H,O)/LANL2DZ(Au)水平上,对OHBA分子进行了结构优化,在此基础上计算了OHBA分子的NRS光谱以及其吸附在Au纳米颗粒上两种不同吸附构型下的SERS光谱,并和实验值进行比较。结果表明,OHBA分子通过羧基吸附构型的计算值比通过羟基吸附构型的计算值与实验值符合的更好。最后,利用GaussView可视化软件对其振动模式进行了全面归属。通过对邻羟基苯甲酸分子拉曼谱峰的详细指认能够得出：Au溶胶中的邻羟基苯甲酸分子,是通过羧基倾斜地吸附在Au纳米颗粒表面的。可视化软件直观形象地展示出了该分子的结构特征和分子基团振动情况,对其振动峰位的归属提供了重要依据。本文工作对推进邻羟基苯甲酸在生物医药等领域进一步的应用具有重要作用。     

Density functional theory analysis of CaRgn complexes: (Rg=He, Ne, Ar; n=1–4)

CaRg_n⁺ (Rg=He, Ne, Ar) complexes with n=1–4, are investigated by performing using the B3LYP/6-311+G (3df) density functional theory calculations. The CaHe_n⁺ (n=1–4) complexes are found to be stable. In the case of CaNe_n⁺ and CaAr_n⁺, stable structures and stationary point were found only for n=1 and 2. For n=3 in the C_3V and the D_3h point group as well as for n=4 in the T_d (tetrahedral) point group a saddle point (imaginary frequency) is observed and global minimum could be obtained along the potential energy surface.     

Sensor calibration for off-the-grid spectral estimation

This paper studies sensor calibration in spectral estimation where the true frequencies are located on a continuous domain. We consider a uniform array of sensors that collects measurements whose spectrum is composed of a finite number of frequencies, where each sensor has an unknown calibration parameter. Our goal is to recover the spectrum and the calibration parameters simultaneously from multiple snapshots of the measurements. In the noiseless case with an infinite number of snapshots, we prove uniqueness of this problem up to certain trivial, inevitable ambiguities based on an algebraic method, as long as there are more sensors than frequencies. We then analyze the sensitivity of this algebraic technique with respect to the number of snapshots and noise.We next propose an optimization approach that makes full use of the measurements by minimizing a non-convex objective which is non-negative and continuously differentiable over all calibration parameters and Toeplitz matrices. We prove that, in the case of infinite snapshots and noiseless measurements, the objective vanishes only at equivalent solutions to the true calibration parameters and the measurement covariance matrix. The objective is minimized using Wirtinger gradient descent which is proven to converge to a critical point. We show empirically that this critical point provides a good approximation of the true calibration parameters and the underlying frequencies.     

Multidimensional anharmonic calculation of the vibrational frequencies and intensities for the trans and cis isomers of HONO with the use of normal coordinates

The equilibrium geometry and the potential energy and dipole moment surfaces have been determined for the cis and trans isomers of the HONO molecule by an ab initio Moller–Plesset (MP2) calculation with a wide set of atomic orbitals. The multidimensional anharmonic vibrational Schrodinger equations are solved using the variational method with the Hamiltonian and wave functions written in the normal coordinates of cis and trans isomers. All one- and two-dimensional and a number of three-dimensional vibrational problems are solved to obtain the energy levels and vibrational eigenfunctions. The frequencies and intensities for the fundamental, overtone and some combination bands are determined in good agreement with the available experimental results. The calculation shows the strength of coupling between different vibrational modes and reveals the presence of strong resonances between the (v₁, v₃, v₆) and (v₁, v₃−1, v₆+2) states of cis-HONO. This fact may be important for understanding the energy redistribution between the intermolecular degrees of freedom. The magnitude and direction of vibrationally averaged ground-state dipole moment of both isomers, as well as the direction of transition dipole moments, are in good agreement with the experimental findings. The changes in the values of dipole moment and some geometrical parameters of cis- and trans-HONO on vibrational excitation are also computed.     

高温下季戊四醇晶体的结构和振动性质的分子动力学模拟(英文)

通过分子动力学研究了季戊四醇晶体在温度高达500K范围内的结构和振动性质.考察了季戊四醇晶体的晶格参数和分子构型等随温度变化情况,相对晶格常数a来说,晶格常数c容易被压缩.发现C-C,C-H和C-O键随温度的变化较大,这意味着在分解过程中这些键可能较敏感,即最先断裂可能性较大.研究了季戊四醇晶体在不同温度下的振动,发现大部分频率随温度的升高而降低.     

A theoretical and matrix-isolation FT-IR investigation of the conformational landscape of N-acetylcysteine

The conformational landscape of N-acetylcysteine (NAC) has been investigated by a combined experimental matrix-isolation FT-IR and theoretical methodology. This combination is a powerful tool to study the conformational behavior of relatively small molecules. Geometry optimizations at the HF/3-21 level resulted in 438 different geometries with an energy difference smaller than 22 kJ mol⁻¹. Among these, six conformations were detected with a relative energy difference smaller than 10 kJ mol⁻¹ at the DFT(B3LYP)/6-31++G∗∗ level of theory. These were finally subjected to MP2/6-31++G∗∗ optimizations which resulted in five minima. The vibrational and thermodynamical properties of these conformations were calculated at both the DFT and MP2 methodologies. Experimentally NAC was isolated in an argon matrix at 16 K after being sublimated at 323 K. The most stable MP2 form appeared to be dominant in the experimental spectra but the presence of three other conformations with ΔE_MP2 < 10 kJ mol⁻¹ was also demonstrated. The experimentally observed abundance of the H-bond containing conformations appeared to be in good accordance with the predicted MP2 value.     

Line positions and strengths of 41 bands including 10 OCS isotopologues in the 3850-4200 cm region

The present analysis substantially improves the spectroscopic characterization of near infrared OCS in a window region (3850-4200 cm⁻¹) important for atmospheric studies of Venus. Previous studies in this spectral region cataloged numerous OCS line positions, but accurate line intensities were measured for only three strong bands. In this paper, the corresponding line intensities are obtained for 41 OCS bands, including weak isotopic bands reported for the first time. The 2ν₃ (0002-0000) band is analyzed for 10 OCS isotopologues (adding ¹⁶O¹³C³⁴S, ¹⁷O¹²C³²S, ¹⁶O¹²C³⁶S, ¹⁸O¹²C³⁴S, and ¹⁶O¹³C³³S). In addition, observations of 0332-0330 of the main isotope, ¹⁶O¹²C³²S, provides accurate vibration-rotation parameters for the upper state (and the lower state, 0330 of ¹⁶O¹²C³²S). Finally, one unidentified band is seen at 3969.3 cm⁻¹; its lower state is clearly the ground state of ¹⁶O¹²C³²S. The line strengths of these seven previously unanalyzed bands plus 34 other bands of the OCS isotopologues, ¹⁶O¹²C³²S, ¹⁶O¹²C³⁴S, ¹⁶O¹³C³²S, ¹⁶O¹²C³³S, and ¹⁸O¹²C³²S, were least-squares fitted to determine strength parameters, S_v and Herman-Wallis coefficients. Finally, the intensities of 17 additional very weak bands were estimated to provide an extensive new database of OCS line parameters to support remote sensing of Venus. The integrated intensity in cm⁻¹/(molecule cm⁻²) at 296 K is 8.1×10⁻¹⁹ for the 3800-4200 cm⁻¹ region.     

高温下季戊四醇晶体的结构和振动性质的分子动力学模拟

通过分子动力学研究了季戊四醇晶体在温度高达500K范围内的结构和振动性质。考察了季戊四醇晶体的晶格参数和分子构型等随温度变化情况,相对晶格常数a来说,晶格常数c容易被压缩。发现C-C,C-H和 C-O键随温度的变化较大,这意味着在分解过程中这些键可能较敏感,即最先断裂可能性较大。研究了季戊四醇晶体在不同温度下的振动,在常压下,我们所计算的振动频率高于实验结果,另外,我们还讨论了由温度引起的频率漂移。     

Force Constant Calculations Using the “Simplex” Method Application to Imidazolidinetrione (Parabanic Acid)

With the object to improve the results, of least squares refinement of force constants the authors propose an iterative procedure using the “simplex” system and the invariants of similarity. These invariants are calculated by a special way without determination of roots. This method has been applied with satisfaction to parabanic acid.     

The Application of Digital Filtering to Phase Recovery when Surface Contouring using Fringe Projection Techniques

If structured light consisting of parallel stripes, or fringes, is projected onto a surface, then the surface acts as a phase modulator, with the amount of modulation at any point depending upon the height of the surface at that point. In recent years considerable effort has been devoted to the problem of fringe demodulation, with prominence given to techniques using fringe-phase stepping and Fourier analysis. It has long been known that phase demodulation is possible using a system of filters, and the technique has been widely used in the related area of frequency demodulation in radio. In this paper the development of phase demodulation using a system of digital filters is considered. For the accurate recovery of image phase it is necessary for the filters to introduce zero phase shift, or to have a phase shift proportional to frequency. The design of the digital filters is considered and their performance is assessed using the signal from a real modulated fringe pattern and a simulated signal. It is shown that the demodulation technique works well, even with a poor signal-to-noise ratio. © 1997 Elsevier Science Ltd. All rights reserved.