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91.
The theoretical profiles for both principal (τ2=τ1) and harmonic (τ2=1/2τ1, 2τ1) spin echoes in gamma detected triple pulse NMRON experiments are systematically calculated for a wide range of the parameter
for inhomogeneous broadening using analytic expressions derived from physical ensemble rotation considerations, specific to
a pure Zeeman Hamiltonian. In the absence of skin effects, and assuming equal turn angle pulses, these calculations provide
the optimum turn angle conditions for maximum spin echo amplitude. 相似文献
92.
93.
Chaplin AB Hooper JF Weller AS Willis MC 《Journal of the American Chemical Society》2012,134(10):4885-4897
Readily prepared and bench-stable rhodium complexes containing methylene bridged diphosphine ligands, viz. [Rh(C(6)H(5)F)(R(2)PCH(2)PR'(2))][BAr(F)(4)] (R, R' = (t)Bu or Cy; Ar(F) = C(6)H(3)-3,5-(CF(3))(2)), are shown to be practical and very efficient precatalysts for the intermolecular hydroacylation of a wide variety of unactivated alkenes and alkynes with β-S-substituted aldehydes. Intermediate acyl hydride complexes [Rh((t)Bu(2)PCH(2)P(t)Bu(2))H{κ(2)(S,C)-SMe(C(6)H(4)CO)}(L)](+) (L = acetone, MeCN, [NCCH(2)BF(3)](-)) and the decarbonylation product [Rh((t)Bu(2)PCH(2)P(t)Bu(2))(CO)(SMePh)](+) have been characterized in solution and by X-ray crystallography from stoichiometric reactions employing 2-(methylthio)benzaldehdye. Analogous complexes with the phosphine 2-(diphenylphosphino)benzaldehyde are also reported. Studies indicate that through judicious choice of solvent and catalyst/substrate concentration, both decarbonylation and productive hydroacylation can be tuned to such an extent that very low catalyst loadings (0.1 mol %) and turnover frequencies of greater than 300 h(-1) can be achieved. The mechanism of catalysis has been further probed by KIE and deuterium labeling experiments. Combined with the stoichiometric studies, a mechanism is proposed in which both oxidative addition of the aldehyde to give an acyl hydride and insertion of the hydride into the alkene are reversible, with the latter occurring to give both linear and branched alkyl intermediates, although reductive elimination for the linear isomer is suggested to have a considerably lower barrier. 相似文献
94.
K. Wongcharee M. Brungs R. Chaplin Y.J. Hong R. Pillar E. Sizgek 《Journal of Sol-Gel Science and Technology》2002,25(3):215-221
An antireflective film produced by incorporation of polyethylene glycol (PEG) in the sol is compared to one produced using an aged sol. Incorporation of organic polymer in the precursor solution is a more effective method of increasing the porosity of films and transmittance of the glass substrate. Combination of aging and PEG addition increases the potential for the creation of uniformly porous structures. Aging at high oxide concentration enhances condensation and forms large silica particles containing continuous isolated silanol sites which favor PEG adsorption via hydrogen bonding. Film morphology is affected by phase separation in both the sol and during drying of film. Coating uniformity was improved by minimising phase separation during drying. This was achieved by increasing PEG adsorption by silica sol. Using this technique, coated glass with maximum transmittance of 99.7% can be produced by a simple single step coating. 相似文献
95.
K. Nishimura W. D. Hutchison D.H. Chaplin S.J. Harker K. Mori S. Ohya 《Hyperfine Interactions》2001,133(1-4):121-125
The angular distributions of -rays from 142Pr, 147Nd and 144Pm in Pr0.5Nd0.5Ni were investigated by means of low-temperature nuclear orientation. The results show that the Pr and Nd electronic moments order along the c- and a-axis, respectively. Pm ions introduced as a very dilute magnetic impurity, preferentially align with the Nd ions. 相似文献
96.
The amplitudes of the spin echo and the baseline components of gamma detected NMRON signals have been calculated for the pure
Zeeman case using a density matrix approach. Optimum turn angles and the separate and combined influences of line broadening
and skin effect, appropriate to bulk ferromagnetic metals, are examined. For narrow line, zero skin effect samples, the triple
pulse sequence (cos−1(1/√3))−180°−(180°−cos−1(1/√3)) affords the largest principal echo. However, its advantage is diminished with the introduction of either line broadening
or skin effect and is subsequently lost when both these effects are included or either becomes severe. The skin effect distortion
of the spin echo signal can dominate over intermediate-to-broad line distortions, for that range of experimental conditions
generally applicable tometallic ferromagnetic hosts. 相似文献
97.
Summary Instrumental broadening corrections to gel permeation chromatograms have been demonstrated to be of minimal concern when using the newly available high efficiency packing materials. This was demonstrated using -Styragel as packing material on polymer standards with both narrow and broad molecular weight distributions. 相似文献
98.
Summary A simple method of analysis of the 1,2 and 1,4 isomers of naphthoquinone in crude phthalic anhydride has been developed. The sample was first dissolved in water at 60°C to quantitatively hydrolyse the anhydride to phthalic acid.Analysis of the aqueous solution by reversed-phase HPLC using 7525 methanol:water mobile phase resulted in excellent resolution between the phthalic acid and the naphthoquinones and enabled quantitative measurement of each of the naphthoquinones to 0.1 % in crude phthalic anhydride. 相似文献
99.
100.