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61.
We have studied the spectral properties of luminescence of laurdan molecules in glycerin upon excitation at the red edge of the absorption band at different temperatures. The most significant red-wave shift of the spectra (10 nm) for the longwave band of dual fluorescence is observed depending on the excitation wavelength at a low temperature of 260 K when a solvent forms a fairly rigid matrix. At the same time, at increased temperatures of up to 370 K a small bathochromic shift and a change in the shape of the luminescence bands are also recorded reliably. Changes in the excitation spectra were observed when luminescence was recorded in the bands of the LE- and CT states. The difference spectrum responsible for the additional absorption that does not make a contribution to the longwave luminescence component has been isolated. The decay kinetics of both luminescence components have been measured and their expansions in decay constants have been analyzed. The experimental dependences obtained point to the complex mechanism of inhomogeneous broadening of spectra. 相似文献
62.
We have obtained theoretically an expression for the nuclear free precession signal in an inhomogeneously broadened spin system with a complex structure of the NMR spectrum. It is shown that in this case in the nuclear precession signal there appear maxima the moments of whose formation depend on the detuning of the pulse carrier frequency from the central frequencies of the NMR lines, their widths, and the Rabi frequency. The theoretical results are in good agreement with the experimental data on the observation of proton free precession in toluene. We have constructed a physical model explaining the appearance of maxima in the free precession signal of the spin system. 相似文献
63.
D. Nikolić S. Djurović Z. Mijatović R. Kobilarov N. Konjević 《Journal of Applied Spectroscopy》2001,68(6):902-910
A method of simulating the contour of the asymmetric spectral lines of neutral nonhydrogen-like atoms in a plasma is suggested. The methods of nonlinear regression are used to approximate the experimental data by a model function. The method has been checked on the spectral lines emitted by the electric arc stabilized by the walls. The method makes it possible to evaluate the Stark parameters directly from the experimentally obtained shapes of isolated or overlapping spectral lines. 相似文献
64.
Resolution in 1H NMR spectra of solids can be significantly enhanced with fast magic-angle spinning and high magnetic fields. A variable field and spinning speed study up to 25 T and 40 kHz shows that the homogeneous line broadening is inversely proportional to the product of magnetic field strength and spinning speed. The combination of high field and fast speed yields a 1H linewidth approaching the intrinsic limit determined by anisotropy of magnetic susceptibility. An analysis of the anisotropic magnetic susceptibility line broadening is presented. 相似文献
65.
Eric Jourdanneau Tony Gabard Frdric Chaussard Robert Saint-Loup Hubert Berger Elena Bertseva Frdric Grisch 《Journal of Molecular Spectroscopy》2007,246(2):167-179
CARS laboratory experiments were done in the 2905–2925 cm−1 range, in the vicinity of the ν1 band of the methane molecule, for pressures ranging from 1 to 50 bar, and temperatures up to 1100 K. These experiments were carried out in order to retrieve the pressure evolution of the CH4 spectrum, as well as to confirm its temperature dependance. After a brief recall on the theory used to compute pressure broadening coefficients and relaxation rates, we consider the ν3 and ν4 infrared bands of methane for benchmark calculations purposes. Next, we present recent experimental CARS spectra and calculated ones. Lastly, we discuss flame experiments as well as comparisons of temperature retrieval using N2 and CH4 as probe molecules. 相似文献
66.
Jonathan Levine Michael R. Savina Thomas Stephan Nicolas Dauphas Andrew M. Davis Kim B. Knight Michael J. Pellin 《International journal of mass spectrometry》2009,288(1-3):36-43
Resonance ionization mass spectrometry offers extremely high sensitivity and elemental selectivity in microanalysis, but the isotopic precision attainable by this technique has been limited. Measured isotope ratios are sensitive to small fluctuations in the pointing, pulse timing, and wavelength of the resonance lasers. We show that, by minimizing these fluctuations using feedback controls and by power-broadening the optical transitions, we are able to measure chromium isotope ratios with statistics-limited precision better than 1%. Small additional improvements in reproducibility come from careful shaping of the electric field in the region where atoms are photoionized and from minimizing pulse-to-pulse variations in the time-of-flight mass spectrometer through which the photoions travel. The increased reproducibility of isotopic measurements on standard materials has enabled us to detect anomalous chromium isotopic abundances in presolar SiC grains extracted from primitive meteorites. 相似文献
67.
Broadening-independent demodulation for wavelength modulation spectroscopy based on even-order harmonics 总被引:1,自引:0,他引:1
The line broadening of gas absorption spectrum is a significant but unknown factor in traditional demodulation of wavelength modulation spectroscopy, which is a kind of tunable diode laser absorption spectroscopy in weak absorption cases. In this paper, another signal demodulation method based on some simple algebraic operations with the amplitudes of the zero-, second-, and fourth-order harmonics was proposed. With this method the effect of spectrum broadening could be selfeliminated. That makes the amplitude of the demodulated signal is irrelevant to the broadening, and enables the direct and fast measurement without complex simulations and curve fittings in traditional method. 相似文献
68.
We modify a uniform model of single bubble sonoluminescence, in which heat diffusion, water vapor diffusion and chemical reactions
are included to describe the bubble dynamics, and the processes of electron-atom bremsstrahlung, electron-ion bremsstrahlung
and recombination radiation, radiative attachment of electrons to atoms and molecules, line emissions of OH radicals and Na
atoms are taken into account to calculate the light emission. With this model, we compute the light pulse width, the photon
number per flash, the continuum and line spectra and the gas species as the products of chemical reactions, and try to compare
with all the experimental data available. We obtain good agreement with the observations of Ar and Xe bubbles in many cases,
but fail to match the experimental data of the photon number per flash. We also find that for He bubble the computed photon
number is always too small to interpret the observations.
Supported by the National Natural Science Foundation of China (Grant Nos. 10674081 and 10434070) 相似文献
69.
70.
Perdeuterated benzofluoranthenes have slightly shorter retention times than their equivalent unlabeled forms in a DB-5 capillary column. Under column overload conditions, perdeuterated benzofluoranthenes in moderate multifold excesses, which might be encountered in their use as internal standards and carriers for quantitative analysis, are seen to exhibit both normal and reverse solvent effects on their close eluting congeners. In some cases the effects may be used to advantage by knowledgeable analysts, but for the ignorant and unwary the effects can lead to serious errors in identification and quantification. 相似文献