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531.
From optical and thermal bleaching experiments it is concluded that the 400 nm absorption band which appears in Al2O3 after γ-irradiation is a composite V band. One of its components is attributed to the V-OH center which also is responsible for a localized vibrational band at 3316 cm-11 analogous to the one observed for the VOH center in MgO. The irradiation also results in electron trapping at Cr3+ impurity ions to produce a band at 227 nm. Annealing at 170°C destroys the V-OH center by releasing holes which convert the Cr2+ to Cr3+ with an attendant thermoluminescence. 相似文献
532.
Adler C Ahammed Z Allgower C Anderson M Averichev GS Balewski J Barannikova O Barnby LS Baudot J Bekele S Belaga VV Bellwied R Berger J Bichsel H Bland LC Blyth CO Bonner BE Bossingham R Boucham A Brandin A Caines H de la Barca Sánchez MC Cardenas A Carroll J Castillo J Castro M Cebra D Chattopadhyay S Chen ML Chen Y Chernenko SP Cherney M Chikanian A Choi B Christie W Coffin JP Conin L Cormier TM Cramer JG Crawford HJ DeMello M Deng WS Derevschikov AA Didenko L Draper JE Dunin VB Dunlop JC 《Physical review letters》2001,86(21):4778-4782
We report results on the ratio of midrapidity antiproton-to-proton yields in Au+Au collisions at sqrt[s(NN)] = 130 GeV per nucleon pair as measured by the STAR experiment at RHIC. Within the rapidity and transverse momentum range of /y/<0.5 and 0.4
相似文献
533.
Kimmo A Michelsen Daniël LA van den Hove Christoph Schmitz Olivier Segers Jos Prickaerts Harry WM Steinbusch 《BMC neuroscience》2007,8(1):107
Background
Both prenatal stress (PS) and postnatal chronic mild stress (CMS) are associated with behavioral and mood disturbances in humans and rodents. The aim of this study was to reveal putative PS- and/or CMS-related changes in basal spine morphology and density of pyramidal neurons in the rat medial prefrontal cortex (mPFC). 相似文献534.
Crawford CB Sindile A Akdogan T Alarcon R Bertozzi W Booth E Botto T Calarco J Clasie B Degrush A Donnelly TW Dow K Dutta D Farkhondeh M Fatemi R Filoti O Franklin W Gao H Geis E Gilad S Haeberli W Hasell D Hersman W Holtrop M Karpius P Kohl M Kolster H Lee T Maschinot A Matthews J McIlhany K Meitanis N Milner RG Redwine RP Seely J Shinozaki A Sirca S Six E Smith T Tonguc B Tschalaer C Tsentalovich E Turchinetz W van den Brand JF van der Laan J Wang F Wise T Xiao Y Xu W Zhang C Zhou Z Ziskin V 《Physical review letters》2007,98(5):052301
We report the first precision measurement of the proton electric to magnetic form factor ratio from spin-dependent elastic scattering of longitudinally polarized electrons from a polarized hydrogen internal gas target. The measurement was performed at the MIT-Bates South Hall Ring over a range of four-momentum transfer squared Q2 from 0.15 to 0.65 (GeV/c)(2). Significantly improved results on the proton electric and magnetic form factors are obtained in combination with existing cross-section data on elastic electron-proton scattering in the same Q2 region. 相似文献
535.
Spontaneous enzymatically mediated dynamic kinetic resolution of 8-amino-5,6,7,8-tetrahydroquinoline
A spontaneous dynamic kinetic resolution of 8-amino-5,6,7,8-tetrahydroquinoline 1 was observed in the presence of Candida antarctica Lipase B, in which a >60% yield of (R)-acetamide [(R)-2] was isolated from the racemic amine. The spontaneous formation of ketone 3, followed by a condensation/hydrolysis sequence with the remaining (S)-amine 1, via enamine 4, provides the necessary racemization pathway. 相似文献
536.
537.
Brownridge S Crawford MJ Du H Harcourt RD Knapp C Laitinen RS Passmore J Rautiainen JM Suontamo RJ Valkonen J 《Inorganic chemistry》2007,46(3):681-699
The bonding in the highly homoatomic np pi-np pi (n > or = 3)-bonded S2I42+ (three sigma + two pi bonds), the Se-I pi-bonded Se2I42+ (four sigma + one pi bonds), and their higher-energy isomers have been studied using modern DFT and ab initio calculations and theoretical analysis methods: atoms in molecules (AIM), molecular orbital (MO), natural bond orbital (NBO), and valence bond (VB) analyses, giving their relative energies, theoretical bond orders, and atomic charges. The aim of this work was to seek theory-based answers to four main questions: (1) Are the previously proposed simple pi*-pi* bonding models valid for S2I42+ and Se2I42+? (2) What accounts for the difference in the structures of S2I42+ and Se2I42+? (3) Why are the classically bonded isolobal P2I4 and As2I4 structures not adopted? (4) Is the high experimentally observed S-S bond order supported by theoretical bond orders, and how does it relate to high bond orders between other heavier main group elements? The AIM analysis confirmed the high bond orders and established that the weak bonds observed in S2I42+ and Se2I42+ are real and the bonding in these cations is covalent in nature. The full MO analysis confirmed that S2I42+ contains three sigma and two pi bonds, that the positive charge is essentially equally distributed over all atoms, that the bonding between S2 and two I2+ units in S2I42+ is best described by two mutually perpendicular 4c2e pi*-pi* bonds, and that in Se2I42+, two SeI2+ moieties are joined by a 6c2e pi*-pi* bond, both in agreement with previously suggested models. The VB treatment provided a complementary approach to MO analysis and provided insight how the formation of the weak bonds affects the other bonds. The NBO analysis and the calculated AIM charges showed that the minimization of the electrostatic repulsion between EI2+ units (E = S, Se) and the delocalization of the positive charge are the main factors that explain why the nonclassical structures are favored for S2I42+ and Se2I42+. The difference in the structures of S2I42+ and Se2I42+ is related to the high strength of the S-S pi bond compared to the weak S-I sigma bond and the additional stabilization from increased delocalization of positive charge in the structure of S2I42+ compared to the structure of Se2I42+. The investigation of the E2X42+ series (E = S, Se, Te; X = Cl, Br, I) revealed that only S2I42+ adopts the highly np pi-np pi (n > or = 3)-bonded structure, while all other dications favor the pi-bonded Se2I42+ structure. Theoretical bond order calculations for S2I42+ confirm the previously presented experimentally based bond orders for S-S (2.1-2.3) and I-I (1.3-1.5) bonds. The S-S bond is determined to have the highest reported S-S bond order in an isolated compound and has a bond order that is either similar to or slightly less than the Si-Si bond order in the proposed triply bonded [(Me3Si)2CH]2(iPr)SiSi triple bond SiSi(iPr)[CH(SiMe3)2]2 depending on the definition of bond orders used. 相似文献
538.
Crawford TD Sherrill CD Valeev EF Fermann JT King RA Leininger ML Brown ST Janssen CL Seidl ET Kenny JP Allen WD 《Journal of computational chemistry》2007,28(9):1610-1616
PSI3 is a program system and development platform for ab initio molecular electronic structure computations. The package includes mature programming interfaces for parsing user input, accessing commonly used data such as basis‐set information or molecular orbital coefficients, and retrieving and storing binary data (with no software limitations on file sizes or file‐system‐sizes), especially multi‐index quantities such as electron repulsion integrals. This platform is useful for the rapid implementation of both standard quantum chemical methods, as well as the development of new models. Features that have already been implemented include Hartree‐Fock, multiconfigurational self‐consistent‐field, second‐order Møller‐Plesset perturbation theory, coupled cluster, and configuration interaction wave functions. Distinctive capabilities include the ability to employ Gaussian basis functions with arbitrary angular momentum levels; linear R12 second‐order perturbation theory; coupled cluster frequency‐dependent response properties, including dipole polarizabilities and optical rotation; and diagonal Born‐Oppenheimer corrections with correlated wave functions. This article describes the programming infrastructure and main features of the package. PSI3 is available free of charge through the open‐source, GNU General Public License. © 2007 Wiley Periodicals, Inc. J Comput Chem, 2007 相似文献
539.
Christina L. Crawford Stephan Graf Marc Gonin Katrin Fuhrer Xing Zhang Herbert H. HillJr. 《International Journal for Ion Mobility Spectrometry》2011,14(1):23-30
Increasing the dimensionality of an analysis enables more detailed and comprehensive investigations of complex mixtures. One
dimensional separation techniques like gas chromatography (GC) and ion mobility spectrometry (IMS) provide limited chemical
information about complex mixtures. The combination of GC, ion mobility spectrometry, and time-of-flight mass spectrometry
(GC-IM-TOFMS) provides three-dimensional separation of complex mixtures. In this work, a hybrid GC-IM-TOFMS with a secondary
electrospray ionization (SESI) source provided four types of analytical information: GC retention time, ion mobility drift
time, mass-to-charge ratios, and ion intensity. The use of secondary electrospray ionization enables efficient and soft ionization
of gaseous sample vapors at atmospheric pressure. Several complex mixtures, including lavender and peppermint essential oils,
were analyzed by GC-SESI-IM-TOFMS. The resulting 3D data from these mixtures, each containing greater than 50 components,
were plotted as 3D projections. In particular, post-processed data plotted in three dimensions showed that many mass selected
GC peaks were resolved into different ion mobility peaks. This technique shows clear promise for further in-depth analyses
of complex chemical and biological mixtures. 相似文献
540.
We present the first calculations of Raman optical activity spectra at the coupled-cluster level of theory. Calculations are presented for (S)-methyloxirane and compared to recent experimental gas-phase measurements as well as the results obtained at the Hartree-Fock and density functional level of theory using the popular B3LYP functional. For the experimentally relevant frequency region of 400-1600 cm(-1), the Hartree-Fock, B3LYP and coupled-cluster spectra are very similar when the same force field is used, and the results also agree well with experiment. For high-frequency vibrational modes, differences in the ROA difference parameters are observed and are analyzed. The new coupled-cluster ROA code will allow for critical benchmarking of the accuracy of modern exchange-correlation functionals in the calculation of ROA spectra. 相似文献