苦瓜中维生素C含量的测定

建立苦瓜中维生素C含量直接测定新方法。以10%盐酸溶液为溶剂,采用紫外分光光度法测定含量。维生素C在0—10μg/mL浓度范围内与吸光度呈良好的线性关系,回归方程为：y=0.04746C＋0.00109,r=0.9997。检出限为0.023μg/mL,加标回收率在94.8%—101.1%之间。该法操作简单,干扰离子少,结果准确,测量快速、准确度和灵敏度高,可应用于维生素C含量的测定。     

Energy structure and absorption spectra of colloidal CdS nanocrystals in gelatin matrix

We investigate the energy structure of colloidal CdS nanocrystals by measuring the UV–vis absorption spectra. Nanocrystals were synthesized by sol–gel method in a gelatin matrix in the size range from 2.5 to 3.9 (±0.2) nm. In order to interpret the UV–vis absorption spectra we calculate the energy spectrum of electron quasi-stationary states using the model of open nanocrystal as well as the hole stationary spectrum in a two-band approach. It is shown that the main contribution to the absorption spectrum is made by interband transitions 1S_3/2→1S_e and 1P_3/2→1P_e, and its shape is determined by the size distribution of nanoparticles. For this system the estimated values of the effective masses of the heavy hole and light hole are 1.44m₀ and 0.28m₀, respectively.     

高灵敏度激光吸收光谱中的微弱信号处理

可调谐二极管激光频率调制吸收光谱（FM-TDLAS）技术是一种高灵敏度的痕量气体检测方法。为改善以CH₄为目标气体检测系统的信噪比,提高系统的检测灵敏度,以双平衡混频器（double balanced mixer）为核心,设计了一套用于提取被噪声淹没的微弱信号的调制解调高频相敏探测器。在对高频相敏探测器进行具体设计和分析的基础上, 结合实验,利用CH₄气体在1653nm附近的近红外吸收光谱,对整体电路的性能进行了测试,获得了具有较高信噪比的二次和一次谐波信号,检测灵敏度可达10×10^-6。     

Doping dependence of the electronic Raman spectra in cuprates

We report electronic Raman scattering measurements on Bi₂Sr₂(Y_1−xCa_x)Cu₂O_8+δ single crystals at different doping levels. The dependence of the spectra on doping and on incoming photon energy is analyzed for different polarization geometries, in the superconducting and in the normal state. We find the scaling behavior of the superconductivity pair-breaking peak with the carrier concentration to be very different in B_1g and B_2g geometries. Also, we do not find evidence of any significant variation in the lineshape of the spectra in the overdoped region in both symmetries, while we observe a reduction of the intensity in B_2g upon decreasing photon energies. The normal state data are analyzed in terms of the memory-function approach. The quasiparticle relaxation rates in the two symmetries display a dependence on energy and temperature which varies with the doping level.     

Electronic state observation of inner organic thin films beneath electrodes: Fluorescence-yield X-ray absorption spectra of pentacene derivative films

The electronic states of inner organic thin films have been investigated by X-ray absorption spectroscopy (XAS) in a bulk-sensitive fluorescence-yield (FY) mode with theoretical analysis. The thin films of the synthesized pentacene derivative, i.e., 6,13-dihydrodiazapentacence (C₂₀N₂H₁₄), on SiO₂-covered Si substrates were fabricated and their morphology and crystallinity were characterized by atomic force microscopy (AFM) and X-ray diffraction (XRD) analysis, respectively. The observed N K-edge FY-XAS spectra were different from the surface-sensitive XAS spectra measured in a partial-electron-yield (PEY) mode. The peaks on the FY-XAS spectra were well reproduced by the theoretical calculation of the unoccupied states of an HAPn molecule. In addition, the incident angle dependence of the FY-XAS spectra was consistent with the expected molecular orientation in the thin films. As a result, we successfully obtained the N and C K-edge FY-XAS spectra of the inner HAPn thin films even beneath Au electrodes.     

Electronic absorption spectra determination of C60 content in soot produced in hydrocarbon flames

We analyze the possibilities of eliminating hydrocarbon compounds from soot produced in hydrocarbon flames for the purpose of using the method of electronic absorption spectra to measure the content of fullerenes. The sensitivity limit of the spectral-absorption method has been determined. The solubility of C₆₀ in ether has been measured. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 67, No. 4, pp. 253–256, March–April, 2000.     

Electronic transitions of fluorene, dibenzofuran, carbazole, and dibenzothiophene: From the onset of absorption to the ionization threshold

A comparative study of the electronic transitions of fluorene and its hetero-analogues dibenzofuran, carbazole, and dibenzothiophene was performed in a wide energy range. Gas phase, crystal phase, and linear dichroism electronic transmittance spectra were measured with synchrotron radiation. Electronic transitions to excited singlet states were predicted with time-dependent density functional theory, TD-B3LYP/6-31+G(d,p). Based on the experimental and theoretical results, symmetry assignments of electronic transitions in the vacuum and near-UV region are suggested. The correspondence between excited states in these molecules, similarities, and differences between their electronic spectra are discussed.     

Solvent effects on electronic absorption spectra of donor‐substituted 11,11,12,12‐tetracyano‐9, 10‐anthraquinodimethanes (TCAQs)

Solvent effects on the electronic absorption spectra of donor‐substituted 11,11,12,12‐tetracyano‐9, 10‐anthraquinodimethanes (TCAQs) 1 – 3 have been investigated in 32 well‐selected solvents. These compounds were chosen as model structures for charge‐transfer chromophores featuring second‐ and third‐order nonlinear optical properties. The resulting data were evaluated by means of theoretical models and (semi)empirical correlations determining the optical properties related to electron distribution and polarizability. We found that solvent effects on a polar D‐π‐A system do not depend on the donor/acceptor orientation (HOMO/LUMO localization) but especially on the length of the π‐system in between. The observed solvent effects are described with high accuracy by the applied theoretical models and linear combinations of physical quantities. Solvent polarization, permanent dipole moment, and molar volume substantially affect the longest‐wavelength absorption maxima. Solvent‐induced bathochromic shift resulting from the solvent polarity is described with high accuracy by the Born function. On the other hand, hypsochromic effects of the solvent permanent dipole moment are caused due to the slower reorganization of molecular dipoles compared with the rate of excitation. Solvent polarizability shifts the longest‐wavelength absorption maxima bathochromically with increasing length of the π‐conjugated system. Whereas this effect could be suitably described by the Onsager‐induced polarizability, the orientation polarizability was not found to be important. The solvent molar volume as a hypsochromic shift‐inducing factor is only relevant if the size of the solute and solvent molecules are comparable. If the size of the solute is considerably larger than that of the solvent molecules, the solvent behaves as a ‘shape continuum.’ Copyright © 2008 John Wiley & Sons, Ltd.     

Pressure effects on the absorption spectra of Na doped in solid Ar

1 Introduction Impelled by the research project for the High Energy Density Matter (HEDM) ofUSA, researchers have achieved fruitful results on the energetic species in cryogenicenvironments[1]. That the chemical performance of solid hydrogen fuel can be greatlyenhanced when being doped with a small amount of light metal is confirmed both theo-retically and experimentally[2]. For understanding the mechanism, similar systems haveattracted much interest. The system of rare gas solid doped w…     

Process Analytical Chemistry: Applications of Ultraviolet/Visible Spectrometry in Environmental Analysis: An Overview

Abstract

Process analyzers based on the selective absorption of the ultraviolet (UV) and/or visible (VIS) radiation provide an on-line monitoring highly reliable of the composition and the industrial process control.

This review provides information about the technological advances in this area and its industrial applications, especially environmental applications.     

Experimental study and calculations of nitric oxide absorption in the γ(0,0) and γ(1,0) bands for strong temperature conditions

Absorption spectra of nitric oxide in the γ(0,0) and γ(1,0) bands have been measured for hard temperature conditions up to 1700 K in order to validate a model for the simulation of these two bands. The good agreement between experiments and calculations (relative errors of 2–5% for the γ(0,0) band and 10–15% for the γ(1,0) band) consolidates the two important assumptions concerning the intermediate Hund's case between (a) and (b) for the X²Π state of the γ(0,0) and γ(1,0) absorption bands and the use of collisional broadening parameters of γ(0,0) to simulate the γ(1,0) band. Using this simulation, a study of the Beer–Lambert law behavior at high temperature has been carried out. With the instrument resolution used for these experiments, it was shown that a correction of the Beer–Lambert law is necessary. To apply this technique for the measurements of NO concentrations inside the combustion chamber of an optical SI engine, a new formulation of the Beer–Lambert law has been introduced, since the modified form proposed in the literature is no longer applicable in the total column range of interest.     

便携式近红外光谱仪测定苹果酸度和抗坏血酸的研究

应用便携式近红外光谱分析仪对6种苹果进行无损检测,运用Kernel Isomap结合广义回归神经网络的方法分别建立苹果酸度和抗坏血酸定量分析模型.结果表明:采用Kernel Isomap方法能够使模型具有良好的预测能力.苹果酸度模型校正集相关系数Rc=0.9994,预测集相关系数Rp=0.979 9,RMSEP=0.0...     

Electronic absorption spectra of Sm(II) and Yb(II) ions in a LiCl-KCl eutectic melt at 450 °C

We have measured the absorption spectra of Sm(II) and Yb(II) ions in LiCl-KCl eutectic at 450 °C. The UV spectra of Sm(II) and Yb(II) exhibited intense and broad peaks at around ∼260 nm, which is attributable to the 4f-5d transitions. With the aid of the UV-vis spectroscopic method, in-situ identification of spontaneous reduction of trivalent Sm and Yb ions to divalent ions was achieved.     

Abnormal effect of hydroxyl on the longest wavelength maximum in ultraviolet absorption spectra for bis‐aryl Schiff bases

Two sets of bis‐aryl Schiff bases that contain 4(or 4′)‐OH and 2(or 2′)‐OH were synthesized. The first set consists of 4‐HOArCH=NArY and XArCH=NArOH‐4′, and the second set consists of 2‐HOArCH=NArY and XArCH=NArOH‐2′. Their ultraviolet absorption spectra were measured and investigated. A very interesting phenomenon was observed by analyzing their wave number ν_max (cm^?1) of longest wavelength maximum λ_max (nm) of ultraviolet. Compared with the change regularity of the ν_max of XArCH=NArY (where the X and Y excluded OH), the 4′‐position hydroxyl (4′‐OH) and 2′‐position hydroxyl (2′‐OH) have abnormal performance. The details are the following: the 4′‐OH contributes an additional red shift to the ν_max of XArCH=NArOH‐4′ (λ_max increase), whereas the 2′‐OH contributes an additional blue shift to the ν_max of XArCH=NArOH‐2′ (λ_max decrease). In addition, there are ortho steric effects of all 2‐OH and 2′‐OH on the ν_max for 2‐HOArCH=NArY and XArCH=NArOH‐2′, and the ortho steric effect contributes a red shift to their ν_max. These experimental facts can provide an important theoretical reference for us using aryl Schiff base compounds as optical materials and performing the molecular design.     

Photochemical conversion and optical absorption spectra of V centers in coloured KI crystals

Abstract

The initial V₂ and V₃ bands observed after quenching of coloured KI crystals are found to be the superposition of absorption bands due to two kinds of V centres with ?110? and ?111? symmetries. The ratio of concentrations of the former to the latter V centers is estimated to be about 3:1. When a quenched crystal is irradiated at 19 K with V₃-light in the 270-nm region, V centers are bleached forming I_2-like centers. On the basis of the I₃ molecule-ion model bound to a cation vacancy, a review is given of recent work on the photochemical conversion of V centers at low temperatures.     

Effect of hydrogen bonding in the vibrational spectra of trans‐cinnamic acid

A computationally‐assisted methodology to assign the vibrational spectra of molecular materials (PiMM) has been successfully applied to the Raman and infrared (IR) spectra of trans‐cinnamic acid (t‐CIA) in the solid state. The effects of molecular association through O H···O hydrogen‐bonding in both the wavenumber and the intensity of the bands are accurately described by a single dimer structure. This supports the discrimination between the possible conformers in the solid, the complete evaluation of hydrogen‐bonding effects, and the full assignment of the vibrational spectra of t‐CIA. Copyright © 2008 John Wiley & Sons, Ltd.     

Solution‐Based Phototransformation of C60 Nanorods: Towards Improved Electronic Devices

A modified liquid–liquid interface precipitation synthesis of C₆₀ nanorods, effects and opportunities following an in situ photochemical transformation in the liquid state, and an electronic characterization using a field‐effect transistor (FET) geometry are reported. The nanorods feature a high aspect ratio of ≈10³ and a notably small average diameter of 172 nm. Interestingly, it is found that a decreased nanorod diameter appears to correlate with distinctly improved electronic properties, and an average electron mobility of 0.30 cm² V^?1 s^?1, as measured in a FET geometry, is reported for as‐grown nanorods, with the peak value being an impressive 1.0 cm² V^?1 s^?1. A photoexposure using green laser light (λ = 532 nm) is demonstrated to result in the formation of a polymer‐C₆₀ shell encapsulating a monomer‐C₆₀ bulk; such photo‐transformed nanorods exhibit an electron mobility of 4.7 × 10^?3 cm² V^?1 s^?1. It is notable that the utilized FET geometry only probes the polymer‐C₆₀ nanorod surface shell, and that the monomer‐C₆₀ bulk is anticipated to exhibit a higher mobility. Importantly, photoexposed nanorods can be conveniently processed as a stabile dispersion in common hydrophobic solvents, and this finding is attributed to the insoluble character of the polymer‐C₆₀ shell.     

Electronic absorption and emission spectra of Alq3 in solution with special attention to a delayed fluorescence

Tris(8-quinolinolato)aluminum(III) (Alq₃) shows electronic absorption bands at 378, 360 (in a 1:1 mixed solvent of methanol and ethanol (ME) at 77 K), 334, 316, 300, 263, 255.8, and 233 nm in ethanol at room temperature. According to the polarized fluorescence excitation spectrum together with MO calculations, for instance, the 360 nm band is assigned to an LL CT transition (an intramolecular charge transfer transition between two ligands), and the 378 nm band to an LM/ML CT one (an intramolecular charge transfer transition between ligand and metal). Alq₃ shows a broad fluorescence band peaking at around 478 nm in the ME matrix at 77 K. The emission spectrum measured with a phosphoroscope has two emission bands at 567 and 478 nm. The 567 nm band accompanies vibronic bands at 578 and 605 nm, being safely assigned to a phosphorescence of Alq₃. The lifetimes of the 478 and 567 nm bands are both 5.4 ms. The lifetime of the 478 nm band together with the band position and its band shape indicate that this band can be assigned to a delayed fluorescence.     

Fourier transform absorption spectra of H2O and H2O in the 8000-9400 cm spectral region

Fourier transform spectra of water vapor enriched in ¹⁸O and ¹⁷O were recorded between 8012 and 9336 cm⁻¹ and analyzed for the first time. High accuracy ab initio predictions of line positions and intensities by Partridge and Schwenke [J. Chem. Phys. 106 (1997) 4618-4639; 113 (2000) 6592-6597] were used in the process of spectrum assignment. Transitions involving the (031), (111), (130), (210), and (012) upper vibrational states were identified in the recorded spectra. As a result, 514 and 244 precise ro-vibrational energy levels were derived for the H₂¹⁸O and H₂¹⁷O molecules, respectively. High-order resonance perturbations between levels of the vibrational states involved were evidenced leading to the identification of a number of rotational levels of the (050) and (060) highly excited bending states.     

Effects of interaction between the chelate rings and π‐conjugated systems in fused salphen complexes on UV‐Vis‐NIR spectra

Dinuclear (Zn₂, Ni₂, and NiZn) complexes of fused salphen with acene‐type annelation were synthesized from 3,7‐diformyl‐2,6‐dihydroxynaphthalene. The spectroscopic properties of these complexes were compared with those of their constitutional isomers with phene‐type annelation. The acene‐type complexes exhibited a characteristic absorption band in the near‐infrared region that showed a noticeable solvent effect. Time‐dependent density functional theory calculations suggested that the absorption arose from a π → π* transition localized at the naphthalene ring, which was perturbed by the adjoining chelate rings. Effects of the connection topology in the fused salphen complexes are discussed by comparison with those of polycyclic aromatic hydrocarbons.