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91.
The ability to characterize individual microscopic particles is important in many areas of science and technology. A variety of microbeam analysis methods are capable of providing information on microscopic particles. With electron probe X-ray microanalysis quantitative analysis is possible under well controlled conditions. Using computer controlled electron microscopes it is feasible to characterize a large number of individual particles. The application of this technique requires the use of multivariate data analysis procedures for the interpretation of the large amount of data obtained. 相似文献
92.
93.
Giavani T Bildsøe H Skibsted J Jakobsen HJ 《Journal of magnetic resonance (San Diego, Calif. : 1997)》2004,166(2):262-272
Experimental strategies for the acquisition of high-quality 14N magic-angle spinning (MAS) NMR spectra of the simple amino acids, which exhibit 14N quadrupole coupling constants (C(Q)) on the order of 1.2 MHz, are devised. These are the first useful 14N MAS spectra reported for nitrogen compounds having a C(Q)(14N) value in excess of 1 MHz. The complete manifolds of spinning sidebands (ssbs), i.e., about 300 ssbs for a spinning frequency of 6.0 kHz, have been observed in the 14N MAS NMR spectra of a series of amino acids. In their crystal structure these amino acids all exhibit the zwitterionic form and thus the 14N MAS NMR spectra represent those of a rotating -NH(3)(+) group and not of an amino (-NH(2)) group. Computer simulations combined with fitting of simulated to the experimental ssb intensities result in the determination of precise values for the 14N quadrupole coupling (C(Q)) and its associated asymmetry parameter (eta(Q)) for the nitrogen sites in these molecules. For some of the amino acids the 14N MAS NMR spectra exhibit overlap between the manifolds of ssbs from two different nitrogen sites in accordance with their crystal structures. Computer analysis of these spectra results in two different sets of (C(Q), eta(Q)) values which mainly differ in the magnitudes for eta(Q). 相似文献
94.
Andersen MD Jakobsen HJ Skibsted J 《Journal of magnetic resonance (San Diego, Calif. : 1997)》2005,173(2):209-217
Asymmetries in the manifold of spinning sidebands (ssbs) from the satellite transitions have been observed in variable-temperature 27Al MAS NMR spectra of alum (KAl(SO4)2.12H2O), recorded in the temperature range from -76 to 92 degrees C. The asymmetries decrease with increasing temperature and reflect the fact that the ssbs exhibit systematically different linewidths for different spectral regions of the manifold. From spin-echo 27Al NMR experiments on a single-crystal of alum, it is demonstrated that these variations in linewidth originate from differences in transverse (T2) relaxation times for the two inner (m=1/2<-->m=3/2 and m=-1/2<-->m=-3/2) and correspondingly for the two outer (m=3/2<-->m=5/2 and m=-3/2<-->m=-5/2) satellite transitions. T2 relaxation times in the range 0.5-3.5 ms are observed for the individual satellite transitions at -50 degrees C and 7.05 T, whereas the corresponding T1 relaxation times, determined from similar saturation-recovery 27Al NMR experiments, are almost constant (T1=0.07-0.10 s) for the individual satellite transitions. The variation in T2 values for the individual 27Al satellite transitions for alum is justified by a simple theoretical approach which considers the cross-correlation of the local fluctuating fields from the quadrupolar coupling and the heteronuclear (27Al-1H) dipolar interaction on the T2 relaxation times for the individual transitions. This approach and the observed differences in T2 values indicate that a single random motional process modulates both the quadrupolar and heteronuclear dipolar interactions for 27Al in alum at low temperatures. 相似文献
95.
By the use of a wide-bore WCOT capillary column, it was possible to obtain the first on-the-fly GC/FT-IR spectra with a WCOT column. This wide-bore WCOT column gave improved separation, as compared to a SCOT column, and yielded identifiable infrared spectra for a real sample. 相似文献
96.
The signs of all 13C? 19F and 1H–19F coupling constants in fluorobenzene, some substituted derivatives, and in 2-fluoropyridine have been related using single-frequency 13C? {1H} double resonance techniques. All 13C? 19F couplings in these compounds are shown to be positive. Direct experimental proof is given for a positive sign for the small five-bond 1H? 19F coupling constant (=0.2—0.3 Hz) in fluorobenzene. The positive sign for 4J(C-4, F) in fluorobenzene is in accord with a positive π-electron contribution to this coupling. 相似文献
97.
98.
A non-linear least-squares program for the analysis of Mössbauer spectra is presented. The program is capable of resolving very complex spectra and can be used on a minicomputer system, with regard to both calculation time and memory requirements. The commonly used x2-minimization algorithm was slightly adapted, so as to broaden its working range. All possibilities for fixing or changing parameters are provided. Two new parameter limitation techniques, which greatly reduce the need for manual intervention during the fitting process, are discussed extensively. 相似文献
99.
Different substituents have been introduced into the 5-position of 2-t-butoxythiophene and by subsequent acid-catalyst dealkylation the corresponding hydroxythiophenes (or their different tautomeric forms) have been isolated in high yields. By NMR, IR and UV-spectroscopy the constitution and the composition of the different tautomeres have been determined. The reaction between carbonyl compounds and 5-t-butoxy-2-thiophenelithium gives carbinols, which upon heating with p-toluenesulphonic acid yielded 5-methylene-3-thiolen-2-ones. 相似文献
100.
The 31P? 31P and 13C? 31P coupling constants in 1,6-diphosphatriptycene have been obtained from analysis of its proton decoupled 13C n.m.r. spectra. More accurate data, however, resulted from simultaneous analysis of the proton decoupled 13C spectra and 31P(13C) satellite spectra. The 13C? 31P couplings are strongly influenced by the proximity and orientation of the phosphorus lone pair electrons. The first 31P? 31P coupling in an aromatic diphosphine is reported. 相似文献