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121.
The infrared emission of CO trapped in solid Ne and Ar is observed at low temperature. The first vibrational level of 12C16O is excited by a Q-switched frequency doubled CO2 laser. The emission spectrum consists of several lines arising from upper vibrational levels of 12C16O and also of 13C16O and 12C18O which are present in natural abundance. An interpretation is proposed which is based on the assumption that long range dipole—dipole interaction is the main physical process involved in these experiments. Resonance energy transfer produces an energy migration among 12C16O molecules without any change in vibrational populations. Phonon assisted energy transfer takes place between vibrational levels of the various isotopic species present in the solution. In order to satisfy the resonance condition a phonon is emitted or absorbed whose energy compensates for the energy mismatch between the transitions in each interacting molecule due to isotopic effect and or vibrational anharmonicity. The range of this process is greatly extended by energy migration. At the low phonon bath temperature phonon emission is much more probable than phonon absorption. So a strong excitation of upper vibrational levels with in some cases population inversions is observed.Molecular impurities act as efficient quenching centers even at very low concentration. When highly purified samples are used, the fluorescence decay time is found to be 20.6 ms in Ne and 14.5 ms in Ar and does not significantly depend upon concentration and temperature. It is concluded that radiationless relaxation is unimportant. 相似文献
122.
J. L. Q. de Britto A. M. S. Braghirolli A. G. da Silva 《Journal of Radioanalytical and Nuclear Chemistry》1985,96(2):181-186
A new and simplified method was developed for the separation of thallium 201 which will allow the shipment of a “one shot generator” to distant places and easy elution at the destination. Thallium is produced as usually, through the reaction $${}^{nat}Tl/p,xn/^{201} pb\xrightarrow{{\beta ^ + }}{}^{201}Tl$$ with 24-MeV protons from IEN'S CV-28 cyclotron. The separation is based on the properties of a chelating carboxylic acid cation exchange resin column which at pH 4.5 retains lead while thallim is easily eluted. This column can also be used as a regular generator to produced greater quantities of201Tl but at the expense of more elutions. 相似文献
123.
S.A.Vieira Filho L.P. Duarte G.D.F. Silva O.W. Howarth I.S. Lula 《Helvetica chimica acta》2003,86(10):3445-3449
3β‐(Stearyloxy)olean‐12‐ene was isolated from a hexane extract of Austroplenckia populnea Reiss (Celastraceae) leaves. The structure was solved by means of quantitative 13C‐NMR, HMBC, HMQC, COSY, NOESY, and NOE difference spectra. The mass spectrum showed an [M+1]+ ion peak at m/z 693, and the molecular formula C48H84O2 was confirmed by combustion analysis. 相似文献
124.
Ur?ka L. ?tangar Urh ?ernigoj Polonca Treb?e Ksenija Maver Silvia Gross 《Monatshefte für Chemie / Chemical Monthly》2006,1(6):647-655
Transparent TiO2 films with a high photodegradation activity towards an azo dye in aqueous solution were prepared by sol–gel processing. Films
on soda–lime glass supports protected with a thin silica barrier layer exhibited better crystallization and monodisperse nanoparticles,
higher absorption of light below 370 nm, and higher photocatalytic activity than those films deposited on bare glass supports
proving the detrimental effect of interdiffused sodium ions on the development of the anatase nanostructure. The effect of
substrate was more pronounced in thinner films (300 nm) than in thicker ones (1200 nm), which were achieved by adding a template
(i.e. Pluronic F127) to the sol. 相似文献
125.
Theoretical aspects of the MS Xα method are analyzed. It is shown that real field self-consistency is not achieved in an MS Xα calculation and some consequences of this fact are discussed. The approximations involved in the use of the transition-state procedure to evaluate ionization and excitation energies from a MS Xα calculation are presented in some detail and commented. 相似文献
126.
J. M. Hernndez Ana M. Herrera J. García‐Serrano J. F. Rivas‐Silva 《International journal of quantum chemistry》2002,88(3):342-346
Conformations of p‐methacryloylaminophenylarsonic acid (p‐MAPHA) are determined through molecular mechanics and DFT/B3LYP calculations. Solvation effects are studied within the self‐consistent isodensity continuum model (SCI‐PCM). The stationary points were found to correspond to minima as verified by the analysis of vibrational frequencies in the molecule. The molecular optical absorption was obtained by using different solvent environments. The present results are in good agreement with the available experimental data. © 2002 Wiley Periodicals, Inc. Int J Quantum Chem, 2002 相似文献
127.
Maria Fernanda Silva Estela Soledad Cerutti Luis D. Martinez 《Mikrochimica acta》2006,155(3-4):349-364
The purpose of this article is to review and evaluate cloud point extraction of metals and its coupling to different contemporary
instrumental methods of analysis. This review covers a selection of the literature published on this topic over the period
mainly between 1997 and September 2005 (consisting of 50 publications). The current state of the art for CPE concerning metals
and metal chelates is presented with special emphasis on the hyphenation of this interesting extraction/preconcentration approach
mediated by surfactants to spectrophotometry, atomic spectroscopy and separation techniques. We present contemporary CPE developments
concerning metal speciation and determination and their application to different environmental, clinical, geological and food
samples. Strategies for method development as well as future perspectives are also covered. 相似文献
128.
Pinotti Laura M. Silva Rosineide G. Giordano Roberto C. Giordano Raquel L. C. 《Applied biochemistry and biotechnology》2002,98(1-9):679-686
This article reports studies concerning the production of penicillin G acylase (PGA) by Bacillus megaterium. This enzyme has industrial use in the hydrolysis of penicillin G to obtain 6-aminopenicillanic acid, an essential intermediate
for the production of semisynthetic β-lactam antibiotics. Although most microorganisms produce the enzyme intracellularly,
B. megaterium provides extracellular PGA. The enzyme production by microorganisms involves several steps, resulting in a many operational
variables to be studied. The study of the inoculum is an important step to be accomplished, before addressing other issues
such as culture optimization and downstream processing. In this study, using a standard inoculum as reference, several runs
were performed aiming at the definition of operational conditions in the PGA production. Cell concentration and PGA activity
in the production medium were measured after 24, 48, and 72 h of the beginning of the production phase. This study encompasses
the duration of the inoculum germination phase and the concentration of cells used to startup the germination. Based on these
results, PGA productivity during the production phase was maximized. The selected values for these variables were 1.5 × 107 spores/mL of germination medium, germination during 24 h, and 72 h for the production phase. 相似文献
129.
E. A. Guimares Costa F. De Brito Mota A. Ferreira Da Silva 《International journal of quantum chemistry》1992,41(3):517-524
The density of states is calculated for a random distribution of donor-pairs of hydrogenlike impurities in three- and two-dimensional systems. Recent investigations of the hydrogen molecule in the alternant–molecular–orbital approximation are here extended. We found that the lowest excited state 1Σu (i.e., H+H?), which is optically connected to the ground state, plays a relevant role in the absorption spectra of semiconductor systems. 相似文献
130.
This determination of salicylate in blood serum is based on application of an immobilized enzyme electrode. Salicylate hydroxylase (E.C.1.14.13.1) is chemically immobilized onto a pig intestine mounted on an oxygen electrode. The signals are monitored amperometrically and the resulting output voltage is read using a simple adapter. The experimental parameters and possible interferences are discussed. Samples containing 1.0 × 10?5?1.87 × 10?3 M (1.6–300 μg ml?1) salicylate were assayed with relative standard deviations between 1.3% and 6% and recoveries between 98.7 and 103%. Results obtained by the proposed method and by the established clinical method for randomly spiked pooled serum samples correlated well (r = 0.99). 相似文献