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31.
The radical yields and rate constants in the quenching reaction of thionine triplet with the complete series of monohalogen substituted anilines as electron donors were determined by flash spectroscopy. Whereas the quenching rate constants show little and unsystematic variation, the radical yields decrease with increasing spin—orbit coupling constant of the halogen substituent. This effect is very sensitive to the position of the halogen in the donor. The results are explained in terms of a heavy atom effect on the intersystem crossing rate constant in a triplet exciplex. 相似文献
32.
The applicability of the carbon paste electrode to the determination of trace quantities of mercury has been investigated in a base electrolyte of 0.1 N KSCN + 0.025 N HCl containing 25 ng/ml copper. The detection limit of the mercury determination has a value near 2.5 ng/ml (1.25×10?8 M), if pre-electrolysis is carried out 10 min at ?1.0 V and the current voltage curve is registered with a scan rate of 16.7 mV/sec between ?0.5 and +0.5 V. The peak height is directly proportional to the concentration in the range from 1.25×10?8 to 1.25×10?6 M. With appropriate preconditioning the carbon paste electrode can be used for several measurements without renewing the surface. 相似文献
33.
Mass-selected gas-phase UV spectra of laser-desorbed molecules at room temperature have been measured via resonance-enhanced multiphoton ionisation (REMPI) and time-of-flight mass selection. The wavelength range of 260 to 320 nm is optimal for detection of polycyclic aromatic hydrocarbons (PAHs) using REMPI-mass spectrometry. A new laser desorption/laser ionisation source has been used which features a compact size and thermal equilibrium of the desorbed molecules. 16 PAHs have been investigated which have been selected by the US Environmental Protection Agency (EPA). These 16 EPA-PAHs are commonly used world-wide to characterise the PAH-load of environmental samples. 相似文献
34.
B. T. Ulrich 《Zeitschrift für Angewandte Mathematik und Physik (ZAMP)》1978,29(2):359-361
A voltmeter of sensitivity
is based on direct conversion of the voltage to be measured into a frequency according to the Josephson voltage-frequency relation. Selfpumped parametric amplification in a d.c. biased loop containing two Josephson junctions and a measuring resistanceR
s=4.7×10–9 amplifies the femptovolt level voltages acrossR
s to microvolt levels that can be observed with a room temperature amplifier. The sensitivity of the femptovoltmeter is determined by Johnson-Nyquist noise voltages at 4.2 K in the 4.7×10–9 resistance. 相似文献
35.
Robert F. Kirchner Gilda H. Loew Ulrich T. Mueller-Westerhoff 《Theoretical chemistry accounts》1976,41(1):1-6
An iterative extended Hückel molecular orbital calculation was used to obtain wave functions for the ground state of ferrocene and several low lying states of the ferrocenium ion. Photoemission spectra in terms of relative ionization potentials and the electric field gradient at the iron nucleus were calculated for ferrocene andg values and the electric field gradient were calculated for the ferrocenium ion. These values are in good agreement with experiment. The nature of the molecular orbitals was compared with results of previous semi-empirical andab initio calculations. 相似文献
36.
Ulrich Vgeli Wolfgang von Philipsborn Kuppuswamy Nagarajan Mohan D. Nair 《Helvetica chimica acta》1978,61(2):607-617
Heterocyclic compounds obtained by addition of acetylenedicarboxylic acid esters to thioureas, cyclic amidines and o-difunctionalized aromatic systems have been studied by 13C-NMR. In particular, C, H-spin-coupling constants over two and three bonds were used to differentiate between the various constitutional isomers and to establish the configuration of trisubstituted exocyclic C, C-double bonds. The configurational significance and diagnostic value of vicinal cis and trans C,H-spin coupling is again demonstrated in the present series. 相似文献
37.
Zusammenfassung Die durch direkte Silylierung von Carbonamidgruppen mit Halogensilanen nicht zugänglichen Verbindungen der Gruppierung R-CONHSiR3
konnten durch Umsetzung von Säureamiden oder Säurechloriden mit Hexamethyldisilazan gewonnen werden. So wurden Derivate mit R=CH3, C2H5, C6H5, CONHSiR3
, OCH3, OC2H5, OCH(CH3)2; R=CH3 (vgl. Tab. 1) dargestellt und in ihren physikalischen und chemischen Eigenschaften näher studiert.Herrn Prof. Dr.A. Zinke zum 70. Geburtstag gewidmet.15. Mitt.:U. Wannagat undH. Kuckertz, Angew. Chem.74, 117 (1962).Auszug aus der DissertationJ. Pump, Techn. Hochsch. Aachen 1962. 相似文献
38.
Molecular mechanics calculations indicate that the deformed chair and twisted-boat conformations are similar in energy for a 4,4-dimethyl-3-keto steroid. Earlier dipole moment work on such compounds is discussed. The crystal structure of 4,4-dimethylandrostan-3-on-17β-yl benzoate has been determined. The crystals are orthorhombic, P212121, a = 17.096 (2), b = 22.136 (e), c = 6.217 (1) A. The structure was solved by direct methods and refined by least squares to R ? 0.039, RXXX = 0.038, based on 2168 observed reflections. Ring A is shown to exist in a chair form, deformed as indicated by the calculations. 相似文献
39.
Ulrich Jordis 《Monatshefte für Chemie / Chemical Monthly》1986,117(11):1339-1342
5-Amino-benzo-1,3-dithiol, available by reduction of 5-amino-benzo-1,3-dithiol-2-thion, was elaborated into dithio-oxolinic Acid (6 a). 相似文献
40.
Ulrich Deschler Peter Kleinschmit Peter Panster 《Angewandte Chemie (International ed. in English)》1986,25(3):236-252
Silicon and carbon may be looked upon as the two fundamental antipodes with respect to the naturally occurring forms of matter and life on earth: Silicon plays the key role in the “petrification” of inanimate matter, while carbon is the representative element for the “incarnation” of living organisms. If a scientist were to search for a highly efficient method of uniting inorganic and organic matter, he would, at a very early stage of attempting to solve this problem, combine these two natural principles of matter and think of “bireactive” molecules containing a silicon functionality for bonding to inorganic material on the one hand and a carbon functionality for anchoring to an organic counterpart on the other. The title compounds and their derivatives epitomize such molecules: they are wanderers between both (chemical) worlds. Owing to their bifunctionality they are capable of binding to inorganic (especially siliceous) systems as well as to organic polymers. Whether their commercial application concerns the strengthening of polyester resins with glass fibers for use in boatbuilding or the incorporation of silica as a filler in rubber mixtures for the manufacture of wear-resistant tires or even the immobilization of enzymes on glass spheres for carrying out reactions in enzyme reactors—in all cases organofunctionalized silanes guarantee a reliable and permanent union between two otherwise “incompatible” material systems. 相似文献