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1.
Carl Nordling 《Angewandte Chemie (International ed. in English)》1972,11(2):83-92
A substance on which X-rays fall emits photoelectrons and Auger electrons. The energy spectra of the electrons emitted provide information about the electronic structure in the specimen, ranging from the innermost atomic levels and their dependence on the chemical environment to the molecular orbitals of the valence electrons and the band structure in solids. Electron spectra of this nature can now be recorded with high-resolution instruments; their analysis offers new aspects for investigation of chemical composition. The method of electron spectroscopy developed for this purpose, which has now been developed to a high degree of perfection, will be referred to in the following discussion as ESCA (Electron Spectroscopy for Chemical Analysis). 相似文献
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Dr. Peter D. Dahlberg Davis Perez Dr. Zhaoming Su Prof. Wah Chiu Prof. W. E. Moerner 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2020,132(36):15772-15778
Cryogenic single-particle photoluminescence (PL) spectroscopy has been used with great success to directly observe the heterogeneous photophysical states present in a population of luminescent particles. Cryogenic electron tomography provides complementary nanometer scale structural information to PL spectroscopy, but the two techniques have not been correlated due to technical challenges. Here, we present a method for correlating single-particle information from these two powerful microscopy modalities. We simultaneously observe PL brightness, emission spectrum, and in-plane excitation dipole orientation of CdSSe/ZnS quantum dots suspended in vitreous ice. Stable and fluctuating emitters were observed, as well as a surprising splitting of the PL spectrum into two bands with an average energy separation of 80 meV. In some cases, the onset of the splitting corresponded to changes in the in-plane excitation dipole orientation. These dynamics were assigned to structures of individual quantum dots and the excitation dipoles were visualized in the context of structural features. 相似文献
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LiMeiQIU FenLIU LiangZhongZHAO 《中国化学快报》2003,14(10):1058-1061
The effect of low energy electron (LEE) exposure on ISS, including on the sputter peak and scatter peak as well as on ion neutralization, has been investigated for different samples. Some new results are discussed. 相似文献
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Peter D. Dahlberg Davis Perez Zhaoming Su Wah Chiu W. E. Moerner 《Angewandte Chemie (International ed. in English)》2020,59(36):15642-15648
Cryogenic single‐particle photoluminescence (PL) spectroscopy has been used with great success to directly observe the heterogeneous photophysical states present in a population of luminescent particles. Cryogenic electron tomography provides complementary nanometer scale structural information to PL spectroscopy, but the two techniques have not been correlated due to technical challenges. Here, we present a method for correlating single‐particle information from these two powerful microscopy modalities. We simultaneously observe PL brightness, emission spectrum, and in‐plane excitation dipole orientation of CdSSe/ZnS quantum dots suspended in vitreous ice. Stable and fluctuating emitters were observed, as well as a surprising splitting of the PL spectrum into two bands with an average energy separation of 80 meV. In some cases, the onset of the splitting corresponded to changes in the in‐plane excitation dipole orientation. These dynamics were assigned to structures of individual quantum dots and the excitation dipoles were visualized in the context of structural features. 相似文献
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A new selected-configuration interaction method is proposed, based on the use of local orbitals. A corresponding code has been written, which is devoted to CI calculations of rather large systems (about 50-100 carbon-like atoms). Taking advantage of the locality, and then of the fact that interactions vanish when the distance is large, the dimension of the CI space is largely reduced. The determinants that would be created by long range excitations are expected to have a small weight in the wave function and are therefore eliminated. This selected excitation CI space is particularly suited for large molecules. It is tested on large polyene chains and on a transition metal complex. For large enough systems, the CPU time saving is important and, what is more noticeable, calculations that were impossible to perform without selection are feasible in this approach. 相似文献
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Understanding J‐Modulation during Spatial Encoding for Sensitivity‐Optimized Ultrafast NMR Spectroscopy
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Boris Gouilleux Laetitia Rouger Benoît Charrier Dr. Ilya Kuprov Prof. Serge Akoka Dr. Jean‐Nicolas Dumez Dr. Patrick Giraudeau 《Chemphyschem》2015,16(14):3093-3100
Ultrafast (UF) NMR spectroscopy is an approach that yields 2D spectra in a single scan. This methodology has become a powerful analytical tool that is used in a large array of applications. However, UF NMR spectroscopy still suffers from an intrinsic low sensitivity, and from the need to compromise between sensitivity, spectral width, and resolution. In particular, the modulation of signal intensities by the spin–spin J‐coupling interaction (J‐modulation) impacts significantly on the intensities of the spectral peaks. This effect can lead to large sensitivity losses and even to missing spectral peaks, depending on the nature of the spin system. Herein, a general simulation package (Spinach) is used to describe J‐modulation effects in UF experiments. The results from simulations match with experimental data and the results of product operator calculations. Several methods are proposed to optimize the sensitivity in UF COSY spectra. The potential and drawbacks of the different strategies are also discussed. These approaches provide a way to adjust the sensitivity of UF experiments for a large range of applications. 相似文献
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Yu. I. Tarasov I. V. Kochikov D. M. Kovtun N. Vogt B. K. Novosadov A. S. Saakyan 《Journal of Structural Chemistry》2004,45(5):778-785
For rigid polyatomic molecules, a procedure is described for determining their equilibrium geometrical structures by processing gas-phase electron diffraction, spectroscopy, and quantum-chemical data. The efficiency of the procedure is demonstrated by reference to the 1,2-thiaarsol molecule. For this molecule, quantum-chemical calculations of different degrees of complexity have been carried out, and harmonic and anharmonic force fields have been constructed. The force constants were employed for determining the equilibrium geometry from experimental data. Analysis of the results of this study suggests that the calculated vibrational corrections to the internuclear distances are almost independent of the level of the quantum-chemical calculations.Original Russian Text Copyright © 2004 by Yu. I. Tarasov, I. V. Kochikov, D. M. Kovtun, N. Vogt, B. K. Novosadov, and A. S. Saakyan__________Translated from Zhurnal Strukturnoi Khimii, Vol. 45, No. 5, pp. 822–829. September–October, 2004. 相似文献
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An in situ heating system was built for the Auger electron spectroscopy to investigate the thermal effect of Auger lines. A GaN sample was studied in this system. The kinetic energy of Ga LMM and MVV Auger lines were observed to shift negatively with temperature increasing. By using ab initio calculation, the theoretical Ga MVV Auger line shape was fit, which well reflects the inner property of the line. The Auger shift with heating is related with the valence electron rearrangement in the thermal expansion of the local bonds. 相似文献
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《Analytical letters》2012,45(9):1502-1510
The identification of automotive coatings has become important for forensic scientists to trace suspects. Popular automotive coatings include acrylic, amino, alkyd, nitro, and polyurethane paints. Various pigments and additives are added to the coatings, which may create difficulty in characterization of paint evidence. In this study, Fourier-transform infrared spectroscopy, Raman spectroscopy and scanning electron microscopy-energy dispersive X-ray spectroscopy were used to characterize an eleven-layer paint sample. Most layers were only a few micrometers thick. Infrared spectroscopy has several advantages in identifying resins and additives, while Raman is more effective in characterizing additives and inorganic pigments. Scanning electron microscopy-energy dispersive X-ray spectroscopy provides elemental analysis information. The results reveal that the combination of these techniques provides more accurate paint identification than using them separately. 相似文献
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Katharine G. Lunny Yanice Benitez Yishai Albeck Prof. Daniel Strasser Prof. John F. Stanton Prof. Robert E. Continetti 《Angewandte Chemie (International ed. in English)》2018,57(19):5394-5397
In an effort to characterize the electronic states of ethylenedione, OCCO, photoelectron‐photofragment coincidence (PPC) spectroscopy was applied to measure anions at m/z 56 and 57 using a pulsed discharge of glyoxal vapor and N2O. PPC measurements at a photon energy of 3.20 eV yield photoelectron spectra in coincidence with either neutral photofragments or stable neutral products. The measurements showed that primarily stable neutral products were formed, with photoelectron spectra consistent with the oxyallyl diradical, C3H4O, and acetone enolate radical, C3H5O. The spectra were also found to have features nearly identical to those reported for OCCO and HOCCO by Sanov and co‐workers. The stability of the neutral products, as well as an examination of spectra reported for the oxyallyl anion and acetone enolate show that the previous assignments of OCCO and HOCCO are in error, and are instead attributed here to the oxyallyl diradical, C3H4O, and the acetone enolate radical, C3H5O. 相似文献
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Dr. João Ameixa Dr. Eugene Arthur-Baidoo João Pereira-da-Silva Júlio C. Ruivo Prof. Dr. Márcio T. do N. Varella Prof. Dr. Martin K. Beyer Dr. Milan Ončák Prof. Dr. Filipe Ferreira da Silva Prof. Dr. Stephan Denifl 《Chemphyschem》2022,23(5):e202100834
Ubiquinone molecules have a high biological relevance due to their action as electron carriers in the mitochondrial electron transport chain. Here, we studied the dissociative interaction of free electrons with CoQ0, the smallest ubiquinone derivative with no isoprenyl units, and its fully reduced form, 2,3-dimethoxy-5-methylhydroquinone (CoQ0H2), an ubiquinol derivative. The anionic products produced upon dissociative electron attachment (DEA) were detected by quadrupole mass spectrometry and studied theoretically through quantum chemical and electron scattering calculations. Despite the structural similarity of the two studied molecules, remarkably only a few DEA reactions are present for both compounds, such as abstraction of a neutral hydrogen atom or the release of a negatively charged methyl group. While the loss of a neutral methyl group represents the most abundant reaction observed in DEA to CoQ0, this pathway is not observed for CoQ0H2. Instead, the loss of a neutral OH radical from the CoQ0H2 temporary negative ion is observed as the most abundant reaction channel. Overall, this study gives insights into electron attachment properties of simple derivatives of more complex molecules found in biochemical pathways. 相似文献
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Sandeep Kumar Singh Balkishen Razdan 《Journal of Dispersion Science and Technology》2013,34(4):538-545
This article looks at atomic force microscopy as an important aid to characterize the self-nanoemulsifying formulation of glibenclamide, lovastatin, and carvedilol in conjunction with other sophisticated technique, viz., transmission electron microscopy and photon correlation spectroscopy. Sizes obtained by processing the atomic force microscopy (AFM) image are comparable with those obtained from transmission electron microscope. Although in the present study, the mean particle size obtained from photon correlation spectroscopy does not correlate to the findings of atomic force microscopy and transmission electron microscopy, but the poly-disperse index values correlate well with the findings of AFM and transmission electron microscopy where uniform particle size was observed in aqueous dispersion of self-nanoemulsifying formulation of glibenclamide, lovastatin, and carvedilol. 相似文献
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Wajih Al‐Soufi Prof. Dr. Belén Reija Dr. Suren Felekyan Dr. Claus A. M. Seidel Prof. Dr. Mercedes Novo Prof. Dr. 《Chemphyschem》2008,9(13):1819-1827
Supramolecular binding is a key process in many biological systems and in newly developed supramolecular assemblies. Most of the scientific work on these systems is focused on their structural properties and on the thermodynamics of the association process. However, the underlying dynamics are usually much less known, in spite of the great importance they have during the binding process in these highly dynamic systems. Understanding supramolecular binding in biological systems and controlling the functionality of new synthetic supramolecular systems can only be achieved through knowledge of the structure–dynamics relationship. There is a strong need for suitable techniques which cover the typically wide time interval of the association dynamics and which do not need a perturbation of the system. We briefly review high‐resolution fluorescence correlation spectroscopy (FCS) as a technique to monitor supramolecular dynamics and to give information on how structure determines the dynamics of host–guest association. The comparison of hosts and guests with different structures shows that geometrical and orientational requirements determine the association rate constant, whereas the dissociation is defined by the strength of specific interactions. As model hosts cyclodextrins and micelles are studied. 相似文献
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波性是原子或分子中电子的重要性质,但结构化学教材对电子波性概念的解释不够详尽。为降低学生在学习该概念时的难度,结合教学实践,尝试将电子波性的物理特征描述为微观环境中电子的运动没有确定的轨迹。通过详细的分析与讨论,多数学生较好地理解了电子波性的物理特征,并认识到正是电子的波性与粒性在不同条件下的转换,才产生了能同时体现出电子波粒二象性的衍射图谱。 相似文献
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Gabriele Saleh Dr. Raffaella Soave Dr. Leonardo Lo Presti Prof. Riccardo Destro 《Chemistry (Weinheim an der Bergstrasse, Germany)》2013,19(10):3490-3503
The accurate, experimental charge density distribution, ρ( r ), of the potent antimalarial drug dihydroartemisinin (DHA) has been derived for the first time from single‐crystal X‐ray diffraction data at T=100(2) K. Gas‐phase and solid‐state DFT simulations have also been performed to provide a firm basis of comparison with experimental results. The quantum theory of atoms in molecules (QTAIM) has been employed to analyse the ρ( r ) scalar field, with the aim of classifying and quantifying the key real‐space elements responsible for the known pharmacophoric features of DHA. From the conformational perspective, the bicyclo[3.2.2]nonane system fixes the three‐dimensional arrangement of the 1,2,4‐trioxane bearing the active O? O redox centre. This is the most nucleophilic function in DHA and acts as an important CH???O acceptor. On the contrary, the rest of the molecular backbone is almost neutral, in accordance with the lipophilic character of the compound. Another remarkable feature is the C? O bond length alternation along the O‐C‐O‐C polyether chain, due to correlations between pairs of adjacent C? O bonds. These bonding features have been related with possible reactivity routes of the α‐ and β‐DHA epimers, namely 1) the base‐catalysed hemiacetal breakdown and 2) the peroxide reduction. As a general conclusion, the base‐driven proton transfer has significant non‐local effects on the whole polyether chain, whereas DHA reduction is thermodynamically favourable and invariably leads to a significant weakening (or even breaking) of the O? O bond. The influence of the hemiacetal stereochemistry on the electronic properties of the system has also been considered. Such findings are discussed in the context of the known chemical reactivity of this class of important antimalarial drugs. 相似文献
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A diagram of kinetic modes (DKM), whose parts correspond to different electron transfer types, for any electrode's Fermi energy F and any finite value of its conduction band's width B is studied. Important differences between DKM for any F and B and DKM in a model of a surface molecule for an electrode-reactant system are pointed out. DKM for electrode models with nearly empty and nearly filled conduction bands proposed earlier are discussed. Expressions for outermost curves of DKM are derived for some special cases within these models. 相似文献