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21.
Unimolecular phototautomeric reactions in 4-thiouracil, 1-methyl-4-thiouracil and 6-aza-4-thiouracil were studied using the matrix-isolation technique combined with infrared absorption spectroscopy. For monomers of these compounds, isolated in solid argon at 10 K, an intramolecular proton-transfer photoreaction was observed. Upon UV (lambda > 345 nm) irradiation, the initial oxo-thione forms of 4-thiouracils were converted into the corresponding oxo-thiol tautomers. The photogenerated oxo-thiol isomers were identified by comparing their experimental IR spectra with the spectra theoretically calculated at the DFT(B3LYP)/6-311++G(2d,p) level. Good agreement between the observed and predicted pattern of spectral bands allowed a reliable identification. This is the first report on experimental observation of isomeric forms of 4-thiouracils other than the canonical oxo-thione tautomers. 相似文献
22.
Wieslaw Wojnowski Barbara Becker Karl Peters Eva-Maria Peters Hans Georg von Schnering 《无机化学与普通化学杂志》1987,553(10):287-292
Structure of Pentaphenyldisilane For the first time Pentaphenyldisilane was prepared by Gilman and Goodman. It is produced by the reaction of Ph3SiLi with Ph2ClSiH. The crystal structure presents an ideally staggered conformation. The distance d(Si? Si) = 235.7 pm corresponds to a normal single bond length. This emphasizes the complete relief of the central Si? Si bond by the insertion of only one hydrogen atom. 相似文献
23.
Wieslaw Jamroz 《Optical and Quantum Electronics》1980,12(6):443-447
The dispersion of the third-order electric susceptibilities(; , , –) and(; , 0, 0) of NaCl and KCl monocrystals has been calculated by means of experimental data on the electro-optic Kerr effect. The result has been obtained by using semi-classical models of anharmonic oscillators. An ionic contribution to the electro-optic coefficients has been presented. From the result obtained it follows that the third-order electric susceptibilities are of the order of 10–22 m2 V–2. 相似文献
24.
Ernst Nowak 《Zeitschrift für Physik B Condensed Matter》1981,45(2):173-176
In the Hubbard model for crystals of the AB-type all information on the system is already contained in the set of eigenstates where the number of sites equals the number of electrons or exceeds it by one. We prove this by deriving relations among the eigenstates with different numbers of particles which do not rely on the well-known transformation of electrons to holes. In this context a new good quantum number is identified. We report on results for the one-dimensional case. 相似文献
25.
Contributions to the Chemistry of Silicon-Sulphur Compounds. 46. 29Si-N.M.R. Chemical Shifts of Trialkoxysilylthio Derivatives of Permethylpolysilanes 29Si-N.M.R. chemical shifts of trialkoxysilythio derivatives of permethylpolysilanes of the two series: α, ω-(RO)3SiS(SiMe2)nSSi(OR)3, n = 2, 3, 4, 6 and 1-(RO)3SiS(SiMe2)nMe, n = 2, 4; R = i-Pr, t-Bu and also 31C-NMR shifts are given. The relationship of 29Si-NMR chemical shift from the netto charge at the silicon atom q(Si) which value has been corrected according to the Sandorfy C quantum-chemical model is discussed. The greater reduction of the electron density at silicon in compounds with Si? X bond (X = S, P, Cl) has been explained by a conjugation of the lone of sulphur with the Si? X bonding pair. 相似文献
26.
RESOLUTION OF TWO EMISSION SPECTRA FOR TRYPTOPHAN USING FREQUENCY-DOMAIN PHASE-MODULATION SPECTRA 总被引:1,自引:0,他引:1
Joseph R. Lakowicz Ranjith Jayaweera Henryk Szmacinski Wieslaw Wiczk 《Photochemistry and photobiology》1989,50(4):541-546
We describe a novel application of frequency-domain fluorometry which allows resolution of the decay times and emission spectra of samples which display multi-exponential decay kinetics. This method does not require any previous knowledge about the decay times or any assumptions about the shape of the emission spectra. We record the wavelength-dependent phase angles and modulations (phase angle and modulation spectra) using a number of light modulation frequencies. The data is analyzed by non-linear least-squares to recover the emission spectra and their associated decay times. Phase and modulation spectra (PM Spec) were used to recover the emission spectra associated with the two decay times of tryptophan at pH = 7 (0.54 and 3.44 ns). The emission spectra of these components are centered at 340 and 355 nm, respectively, with the amplitude of the 0.54 ns component contributing 6% to the total emission. These results are in agreement with previous time-resolved studies by Szabo and Rayner [J. Am. Chem. Soc. 102, 554-563 (1980)]. Control experiments were performed on mixtures of N-acetyl-L-tryptophanamide (NATA) and PPD, which demonstrate our ability to recover the spectra and decay times from two component mixtures. NATA itself displayed a single decay time and only one emission spectrum. 相似文献
27.
28.
Wieslaw Pusz 《Letters in Mathematical Physics》1991,21(1):59-67
The natural S U(2) action on the creation and annihilation operators satisfying twisted canonical commutation relations (TCCR) is investigated. It is shown that the Fock representation is the only covariant irreducible representation of TCCR.Partially supported by the program RP.1.10. 相似文献
29.
Werner Georg Nowak 《manuscripta mathematica》1982,39(2-3):277-285
Let G (R) denote the number of lattice points (,) **Z2 in the domain B(R) bounded by the lemniscate (x2+y2)2=2R2 (x2–y2) and put P(R)=G(R)-R2(R2 being the area of B(R)). The purpose of this paper is to determine the order of magnitude of P(R) for large R by proving the asymptotic relation (3). An analogous result is given for the eight curve x4=R2 (x2–y2). 相似文献
30.